// SPDX-License-Identifier: GPL-2.0-only
/* 
 *    Interfaces to retrieve and set PDC Stable options (firmware)
 *
 *    Copyright (C) 2005-2006 Thibaut VARENE <varenet@parisc-linux.org>
 *
 *    DEV NOTE: the PDC Procedures reference states that:
 *    "A minimum of 96 bytes of Stable Storage is required. Providing more than
 *    96 bytes of Stable Storage is optional [...]. Failure to provide the
 *    optional locations from 96 to 192 results in the loss of certain
 *    functionality during boot."
 *
 *    Since locations between 96 and 192 are the various paths, most (if not
 *    all) PA-RISC machines should have them. Anyway, for safety reasons, the
 *    following code can deal with just 96 bytes of Stable Storage, and all
 *    sizes between 96 and 192 bytes (provided they are multiple of struct
 *    pdc_module_path size, eg: 128, 160 and 192) to provide full information.
 *    One last word: there's one path we can always count on: the primary path.
 *    Anything above 224 bytes is used for 'osdep2' OS-dependent storage area.
 *
 *    The first OS-dependent area should always be available. Obviously, this is
 *    not true for the other one. Also bear in mind that reading/writing from/to
 *    osdep2 is much more expensive than from/to osdep1.
 *    NOTE: We do not handle the 2 bytes OS-dep area at 0x5D, nor the first
 *    2 bytes of storage available right after OSID. That's a total of 4 bytes
 *    sacrificed: -ETOOLAZY :P
 *
 *    The current policy wrt file permissions is:
 *      - write: root only
 *      - read: (reading triggers PDC calls) ? root only : everyone
 *    The rationale is that PDC calls could hog (DoS) the machine.
 *
 *      TODO:
 *      - timer/fastsize write calls
 */

#undef PDCS_DEBUG
#ifdef PDCS_DEBUG
#define DPRINTK(fmt, args...)   printk(KERN_DEBUG fmt, ## args)
#else
#define DPRINTK(fmt, args...)
#endif

#include <linux/module.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/string.h>
#include <linux/capability.h>
#include <linux/ctype.h>
#include <linux/sysfs.h>
#include <linux/kobject.h>
#include <linux/device.h>
#include <linux/errno.h>
#include <linux/spinlock.h>

#include <asm/pdc.h>
#include <asm/page.h>
#include <linux/uaccess.h>
#include <asm/hardware.h>

#define PDCS_VERSION    "0.30"
#define PDCS_PREFIX     "PDC Stable Storage"

#define PDCS_ADDR_PPRI  0x00
#define PDCS_ADDR_OSID  0x40
#define PDCS_ADDR_OSD1  0x48
#define PDCS_ADDR_DIAG  0x58
#define PDCS_ADDR_FSIZ  0x5C
#define PDCS_ADDR_PCON  0x60
#define PDCS_ADDR_PALT  0x80
#define PDCS_ADDR_PKBD  0xA0
#define PDCS_ADDR_OSD2  0xE0

MODULE_AUTHOR("Thibaut VARENE <varenet@parisc-linux.org>");
MODULE_DESCRIPTION("sysfs interface to HP PDC Stable Storage data");
MODULE_LICENSE("GPL");
MODULE_VERSION(PDCS_VERSION);

/* holds Stable Storage size. Initialized once and for all, no lock needed */
static unsigned long pdcs_size __read_mostly;

/* holds OS ID. Initialized once and for all, hopefully to 0x0006 */
static u16 pdcs_osid __read_mostly;

/* This struct defines what we need to deal with a parisc pdc path entry */
struct pdcspath_entry {
        rwlock_t rw_lock;               /* to protect path entry access */
        short ready;                    /* entry record is valid if != 0 */
        unsigned long addr;             /* entry address in stable storage */
        char *name;                     /* entry name */
        struct pdc_module_path devpath; /* device path in parisc representation */
        struct device *dev;             /* corresponding device */
        struct kobject kobj;
};

struct pdcspath_attribute {
        struct attribute attr;
        ssize_t (*show)(struct pdcspath_entry *entry, char *buf);
        ssize_t (*store)(struct pdcspath_entry *entry, const char *buf, size_t count);
};

#define PDCSPATH_ENTRY(_addr, _name) \
struct pdcspath_entry pdcspath_entry_##_name = { \
        .ready = 0, \
        .addr = _addr, \
        .name = __stringify(_name), \
};

#define PDCS_ATTR(_name, _mode, _show, _store) \
struct kobj_attribute pdcs_attr_##_name = { \
        .attr = {.name = __stringify(_name), .mode = _mode}, \
        .show = _show, \
        .store = _store, \
};

#define PATHS_ATTR(_name, _mode, _show, _store) \
struct pdcspath_attribute paths_attr_##_name = { \
        .attr = {.name = __stringify(_name), .mode = _mode}, \
        .show = _show, \
        .store = _store, \
};

#define to_pdcspath_attribute(_attr) container_of(_attr, struct pdcspath_attribute, attr)
#define to_pdcspath_entry(obj)  container_of(obj, struct pdcspath_entry, kobj)

/**
 * pdcspath_fetch - This function populates the path entry structs.
 * @entry: A pointer to an allocated pdcspath_entry.
 * 
 * The general idea is that you don't read from the Stable Storage every time
 * you access the files provided by the facilities. We store a copy of the
 * content of the stable storage WRT various paths in these structs. We read
 * these structs when reading the files, and we will write to these structs when
 * writing to the files, and only then write them back to the Stable Storage.
 *
 * This function expects to be called with @entry->rw_lock write-hold.
 */
static int
pdcspath_fetch(struct pdcspath_entry *entry)
{
        struct pdc_module_path *devpath;

        if (!entry)
                return -EINVAL;

        devpath = &entry->devpath;
        
        DPRINTK("%s: fetch: 0x%p, 0x%p, addr: 0x%lx\n", __func__,
                        entry, devpath, entry->addr);

        /* addr, devpath and count must be word aligned */
        if (pdc_stable_read(entry->addr, devpath, sizeof(*devpath)) != PDC_OK)
                return -EIO;
                
        /* Find the matching device.
           NOTE: hardware_path overlays with pdc_module_path, so the nice cast can
           be used */
        entry->dev = hwpath_to_device((struct hardware_path *)devpath);

        entry->ready = 1;
        
        DPRINTK("%s: device: 0x%p\n", __func__, entry->dev);
        
        return 0;
}

/**
 * pdcspath_store - This function writes a path to stable storage.
 * @entry: A pointer to an allocated pdcspath_entry.
 * 
 * It can be used in two ways: either by passing it a preset devpath struct
 * containing an already computed hardware path, or by passing it a device
 * pointer, from which it'll find out the corresponding hardware path.
 * For now we do not handle the case where there's an error in writing to the
 * Stable Storage area, so you'd better not mess up the data :P
 *
 * This function expects to be called with @entry->rw_lock write-hold.
 */
static void
pdcspath_store(struct pdcspath_entry *entry)
{
        struct pdc_module_path *devpath;

        BUG_ON(!entry);

        devpath = &entry->devpath;
        
        /* We expect the caller to set the ready flag to 0 if the hardware
           path struct provided is invalid, so that we know we have to fill it.
           First case, we don't have a preset hwpath... */
        if (!entry->ready) {
                /* ...but we have a device, map it */
                BUG_ON(!entry->dev);
                device_to_hwpath(entry->dev, (struct hardware_path *)devpath);
        }
        /* else, we expect the provided hwpath to be valid. */
        
        DPRINTK("%s: store: 0x%p, 0x%p, addr: 0x%lx\n", __func__,
                        entry, devpath, entry->addr);

        /* addr, devpath and count must be word aligned */
        if (pdc_stable_write(entry->addr, devpath, sizeof(*devpath)) != PDC_OK)
                WARN(1, KERN_ERR "%s: an error occurred when writing to PDC.\n"
                                "It is likely that the Stable Storage data has been corrupted.\n"
                                "Please check it carefully upon next reboot.\n", __func__);
                
        /* kobject is already registered */
        entry->ready = 2;
        
        DPRINTK("%s: device: 0x%p\n", __func__, entry->dev);
}

/**
 * pdcspath_hwpath_read - This function handles hardware path pretty printing.
 * @entry: An allocated and populated pdscpath_entry struct.
 * @buf: The output buffer to write to.
 * 
 * We will call this function to format the output of the hwpath attribute file.
 */
static ssize_t
pdcspath_hwpath_read(struct pdcspath_entry *entry, char *buf)
{
        char *out = buf;
        struct pdc_module_path *devpath;
        short i;

        if (!entry || !buf)
                return -EINVAL;

        read_lock(&entry->rw_lock);
        devpath = &entry->devpath;
        i = entry->ready;
        read_unlock(&entry->rw_lock);

        if (!i) /* entry is not ready */
                return -ENODATA;
        
        for (i = 0; i < 6; i++) {
                if (devpath->path.bc[i] < 0)
                        continue;
                out += sprintf(out, "%d/", devpath->path.bc[i]);
        }
        out += sprintf(out, "%u\n", (unsigned char)devpath->path.mod);
        
        return out - buf;
}

/**
 * pdcspath_hwpath_write - This function handles hardware path modifying.
 * @entry: An allocated and populated pdscpath_entry struct.
 * @buf: The input buffer to read from.
 * @count: The number of bytes to be read.
 * 
 * We will call this function to change the current hardware path.
 * Hardware paths are to be given '/'-delimited, without brackets.
 * We make sure that the provided path actually maps to an existing
 * device, BUT nothing would prevent some foolish user to set the path to some
 * PCI bridge or even a CPU...
 * A better work around would be to make sure we are at the end of a device tree
 * for instance, but it would be IMHO beyond the simple scope of that driver.
 * The aim is to provide a facility. Data correctness is left to userland.
 */
static ssize_t
pdcspath_hwpath_write(struct pdcspath_entry *entry, const char *buf, size_t count)
{
        struct hardware_path hwpath;
        unsigned short i;
        char in[64], *temp;
        struct device *dev;
        int ret;

        if (!entry || !buf || !count)
                return -EINVAL;

        /* We'll use a local copy of buf */
        count = min_t(size_t, count, sizeof(in)-1);
        strscpy(in, buf, count + 1);
        
        /* Let's clean up the target. 0xff is a blank pattern */
        memset(&hwpath, 0xff, sizeof(hwpath));
        
        /* First, pick the mod field (the last one of the input string) */
        if (!(temp = strrchr(in, '/')))
                return -EINVAL;
                        
        hwpath.mod = simple_strtoul(temp+1, NULL, 10);
        in[temp-in] = '\0';     /* truncate the remaining string. just precaution */
        DPRINTK("%s: mod: %d\n", __func__, hwpath.mod);
        
        /* Then, loop for each delimiter, making sure we don't have too many.
           we write the bc fields in a down-top way. No matter what, we stop
           before writing the last field. If there are too many fields anyway,
           then the user is a moron and it'll be caught up later when we'll
           check the consistency of the given hwpath. */
        for (i=5; ((temp = strrchr(in, '/'))) && (temp-in > 0) && (likely(i)); i--) {
                hwpath.bc[i] = simple_strtoul(temp+1, NULL, 10);
                in[temp-in] = '\0';
                DPRINTK("%s: bc[%d]: %d\n", __func__, i, hwpath.path.bc[i]);
        }
        
        /* Store the final field */             
        hwpath.bc[i] = simple_strtoul(in, NULL, 10);
        DPRINTK("%s: bc[%d]: %d\n", __func__, i, hwpath.path.bc[i]);
        
        /* Now we check that the user isn't trying to lure us */
        if (!(dev = hwpath_to_device((struct hardware_path *)&hwpath))) {
                printk(KERN_WARNING "%s: attempt to set invalid \"%s\" "
                        "hardware path: %s\n", __func__, entry->name, buf);
                return -EINVAL;
        }
        
        /* So far so good, let's get in deep */
        write_lock(&entry->rw_lock);
        entry->ready = 0;
        entry->dev = dev;
        
        /* Now, dive in. Write back to the hardware */
        pdcspath_store(entry);
        
        /* Update the symlink to the real device */
        sysfs_remove_link(&entry->kobj, "device");
        write_unlock(&entry->rw_lock);

        ret = sysfs_create_link(&entry->kobj, &entry->dev->kobj, "device");
        WARN_ON(ret);

        printk(KERN_INFO PDCS_PREFIX ": changed \"%s\" path to \"%s\"\n",
                entry->name, buf);
        
        return count;
}

/**
 * pdcspath_layer_read - Extended layer (eg. SCSI ids) pretty printing.
 * @entry: An allocated and populated pdscpath_entry struct.
 * @buf: The output buffer to write to.
 * 
 * We will call this function to format the output of the layer attribute file.
 */
static ssize_t
pdcspath_layer_read(struct pdcspath_entry *entry, char *buf)
{
        char *out = buf;
        struct pdc_module_path *devpath;
        short i;

        if (!entry || !buf)
                return -EINVAL;
        
        read_lock(&entry->rw_lock);
        devpath = &entry->devpath;
        i = entry->ready;
        read_unlock(&entry->rw_lock);

        if (!i) /* entry is not ready */
                return -ENODATA;
        
        for (i = 0; i < 6 && devpath->layers[i]; i++)
                out += sprintf(out, "%u ", devpath->layers[i]);

        out += sprintf(out, "\n");
        
        return out - buf;
}

/**
 * pdcspath_layer_write - This function handles extended layer modifying.
 * @entry: An allocated and populated pdscpath_entry struct.
 * @buf: The input buffer to read from.
 * @count: The number of bytes to be read.
 * 
 * We will call this function to change the current layer value.
 * Layers are to be given '.'-delimited, without brackets.
 * XXX beware we are far less checky WRT input data provided than for hwpath.
 * Potential harm can be done, since there's no way to check the validity of
 * the layer fields.
 */
static ssize_t
pdcspath_layer_write(struct pdcspath_entry *entry, const char *buf, size_t count)
{
        unsigned int layers[6]; /* device-specific info (ctlr#, unit#, ...) */
        unsigned short i;
        char in[64], *temp;

        if (!entry || !buf || !count)
                return -EINVAL;

        /* We'll use a local copy of buf */
        count = min_t(size_t, count, sizeof(in)-1);
        strscpy(in, buf, count + 1);
        
        /* Let's clean up the target. 0 is a blank pattern */
        memset(&layers, 0, sizeof(layers));
        
        /* First, pick the first layer */
        if (unlikely(!isdigit(*in)))
                return -EINVAL;
        layers[0] = simple_strtoul(in, NULL, 10);
        DPRINTK("%s: layer[0]: %d\n", __func__, layers[0]);
        
        temp = in;
        for (i=1; ((temp = strchr(temp, '.'))) && (likely(i<6)); i++) {
                if (unlikely(!isdigit(*(++temp))))
                        return -EINVAL;
                layers[i] = simple_strtoul(temp, NULL, 10);
                DPRINTK("%s: layer[%d]: %d\n", __func__, i, layers[i]);
        }
                
        /* So far so good, let's get in deep */
        write_lock(&entry->rw_lock);
        
        /* First, overwrite the current layers with the new ones, not touching
           the hardware path. */
        memcpy(&entry->devpath.layers, &layers, sizeof(layers));
        
        /* Now, dive in. Write back to the hardware */
        pdcspath_store(entry);
        write_unlock(&entry->rw_lock);
        
        printk(KERN_INFO PDCS_PREFIX ": changed \"%s\" layers to \"%s\"\n",
                entry->name, buf);
        
        return count;
}

/**
 * pdcspath_attr_show - Generic read function call wrapper.
 * @kobj: The kobject to get info from.
 * @attr: The attribute looked upon.
 * @buf: The output buffer.
 */
static ssize_t
pdcspath_attr_show(struct kobject *kobj, struct attribute *attr, char *buf)
{
        struct pdcspath_entry *entry = to_pdcspath_entry(kobj);
        struct pdcspath_attribute *pdcs_attr = to_pdcspath_attribute(attr);
        ssize_t ret = 0;

        if (pdcs_attr->show)
                ret = pdcs_attr->show(entry, buf);

        return ret;
}

/**
 * pdcspath_attr_store - Generic write function call wrapper.
 * @kobj: The kobject to write info to.
 * @attr: The attribute to be modified.
 * @buf: The input buffer.
 * @count: The size of the buffer.
 */
static ssize_t
pdcspath_attr_store(struct kobject *kobj, struct attribute *attr,
                        const char *buf, size_t count)
{
        struct pdcspath_entry *entry = to_pdcspath_entry(kobj);
        struct pdcspath_attribute *pdcs_attr = to_pdcspath_attribute(attr);
        ssize_t ret = 0;

        if (!capable(CAP_SYS_ADMIN))
                return -EACCES;

        if (pdcs_attr->store)
                ret = pdcs_attr->store(entry, buf, count);

        return ret;
}

static const struct sysfs_ops pdcspath_attr_ops = {
        .show = pdcspath_attr_show,
        .store = pdcspath_attr_store,
};

/* These are the two attributes of any PDC path. */
static PATHS_ATTR(hwpath, 0644, pdcspath_hwpath_read, pdcspath_hwpath_write);
static PATHS_ATTR(layer, 0644, pdcspath_layer_read, pdcspath_layer_write);

static struct attribute *paths_subsys_attrs[] = {
        &paths_attr_hwpath.attr,
        &paths_attr_layer.attr,
        NULL,
};
ATTRIBUTE_GROUPS(paths_subsys);

/* Specific kobject type for our PDC paths */
static const struct kobj_type ktype_pdcspath = {
        .sysfs_ops = &pdcspath_attr_ops,
        .default_groups = paths_subsys_groups,
};

/* We hard define the 4 types of path we expect to find */
static PDCSPATH_ENTRY(PDCS_ADDR_PPRI, primary);
static PDCSPATH_ENTRY(PDCS_ADDR_PCON, console);
static PDCSPATH_ENTRY(PDCS_ADDR_PALT, alternative);
static PDCSPATH_ENTRY(PDCS_ADDR_PKBD, keyboard);

/* An array containing all PDC paths we will deal with */
static struct pdcspath_entry *pdcspath_entries[] = {
        &pdcspath_entry_primary,
        &pdcspath_entry_alternative,
        &pdcspath_entry_console,
        &pdcspath_entry_keyboard,
        NULL,
};


/* For more insight of what's going on here, refer to PDC Procedures doc,
 * Section PDC_STABLE */

/**
 * pdcs_size_read - Stable Storage size output.
 * @kobj: The kobject used to share data with userspace.
 * @attr: The kobject attributes.
 * @buf: The output buffer to write to.
 */
static ssize_t pdcs_size_read(struct kobject *kobj,
                              struct kobj_attribute *attr,
                              char *buf)
{
        char *out = buf;

        if (!buf)
                return -EINVAL;

        /* show the size of the stable storage */
        out += sprintf(out, "%ld\n", pdcs_size);

        return out - buf;
}

/**
 * pdcs_auto_read - Stable Storage autoboot/search flag output.
 * @kobj: The kobject used to share data with userspace.
 * @attr: The kobject attributes.
 * @buf: The output buffer to write to.
 * @knob: The PF_AUTOBOOT or PF_AUTOSEARCH flag
 */
static ssize_t pdcs_auto_read(struct kobject *kobj,
                              struct kobj_attribute *attr,
                              char *buf, int knob)
{
        char *out = buf;
        struct pdcspath_entry *pathentry;

        if (!buf)
                return -EINVAL;

        /* Current flags are stored in primary boot path entry */
        pathentry = &pdcspath_entry_primary;

        read_lock(&pathentry->rw_lock);
        out += sprintf(out, "%s\n", (pathentry->devpath.path.flags & knob) ?
                                        "On" : "Off");
        read_unlock(&pathentry->rw_lock);

        return out - buf;
}

/**
 * pdcs_autoboot_read - Stable Storage autoboot flag output.
 * @kobj: The kobject used to share data with userspace.
 * @attr: The kobject attributes.
 * @buf: The output buffer to write to.
 */
static ssize_t pdcs_autoboot_read(struct kobject *kobj,
                                  struct kobj_attribute *attr, char *buf)
{
        return pdcs_auto_read(kobj, attr, buf, PF_AUTOBOOT);
}

/**
 * pdcs_autosearch_read - Stable Storage autoboot flag output.
 * @kobj: The kobject used to share data with userspace.
 * @attr: The kobject attributes.
 * @buf: The output buffer to write to.
 */
static ssize_t pdcs_autosearch_read(struct kobject *kobj,
                                    struct kobj_attribute *attr, char *buf)
{
        return pdcs_auto_read(kobj, attr, buf, PF_AUTOSEARCH);
}

/**
 * pdcs_timer_read - Stable Storage timer count output (in seconds).
 * @kobj: The kobject used to share data with userspace.
 * @attr: The kobject attributes.
 * @buf: The output buffer to write to.
 *
 * The value of the timer field correponds to a number of seconds in powers of 2.
 */
static ssize_t pdcs_timer_read(struct kobject *kobj,
                               struct kobj_attribute *attr, char *buf)
{
        char *out = buf;
        struct pdcspath_entry *pathentry;

        if (!buf)
                return -EINVAL;

        /* Current flags are stored in primary boot path entry */
        pathentry = &pdcspath_entry_primary;

        /* print the timer value in seconds */
        read_lock(&pathentry->rw_lock);
        out += sprintf(out, "%u\n", (pathentry->devpath.path.flags & PF_TIMER) ?
                                (1 << (pathentry->devpath.path.flags & PF_TIMER)) : 0);
        read_unlock(&pathentry->rw_lock);

        return out - buf;
}

/**
 * pdcs_osid_read - Stable Storage OS ID register output.
 * @kobj: The kobject used to share data with userspace.
 * @attr: The kobject attributes.
 * @buf: The output buffer to write to.
 */
static ssize_t pdcs_osid_read(struct kobject *kobj,
                              struct kobj_attribute *attr, char *buf)
{
        char *out = buf;

        if (!buf)
                return -EINVAL;

        out += sprintf(out, "%s dependent data (0x%.4x)\n",
                os_id_to_string(pdcs_osid), pdcs_osid);

        return out - buf;
}

/**
 * pdcs_osdep1_read - Stable Storage OS-Dependent data area 1 output.
 * @kobj: The kobject used to share data with userspace.
 * @attr: The kobject attributes.
 * @buf: The output buffer to write to.
 *
 * This can hold 16 bytes of OS-Dependent data.
 */
static ssize_t pdcs_osdep1_read(struct kobject *kobj,
                                struct kobj_attribute *attr, char *buf)
{
        char *out = buf;
        u32 result[4];

        if (!buf)
                return -EINVAL;

        if (pdc_stable_read(PDCS_ADDR_OSD1, &result, sizeof(result)) != PDC_OK)
                return -EIO;

        out += sprintf(out, "0x%.8x\n", result[0]);
        out += sprintf(out, "0x%.8x\n", result[1]);
        out += sprintf(out, "0x%.8x\n", result[2]);
        out += sprintf(out, "0x%.8x\n", result[3]);

        return out - buf;
}

/**
 * pdcs_diagnostic_read - Stable Storage Diagnostic register output.
 * @kobj: The kobject used to share data with userspace.
 * @attr: The kobject attributes.
 * @buf: The output buffer to write to.
 *
 * I have NFC how to interpret the content of that register ;-).
 */
static ssize_t pdcs_diagnostic_read(struct kobject *kobj,
                                    struct kobj_attribute *attr, char *buf)
{
        char *out = buf;
        u32 result;

        if (!buf)
                return -EINVAL;

        /* get diagnostic */
        if (pdc_stable_read(PDCS_ADDR_DIAG, &result, sizeof(result)) != PDC_OK)
                return -EIO;

        out += sprintf(out, "0x%.4x\n", (result >> 16));

        return out - buf;
}

/**
 * pdcs_fastsize_read - Stable Storage FastSize register output.
 * @kobj: The kobject used to share data with userspace.
 * @attr: The kobject attributes.
 * @buf: The output buffer to write to.
 *
 * This register holds the amount of system RAM to be tested during boot sequence.
 */
static ssize_t pdcs_fastsize_read(struct kobject *kobj,
                                  struct kobj_attribute *attr, char *buf)
{
        char *out = buf;
        u32 result;

        if (!buf)
                return -EINVAL;

        /* get fast-size */
        if (pdc_stable_read(PDCS_ADDR_FSIZ, &result, sizeof(result)) != PDC_OK)
                return -EIO;

        if ((result & 0x0F) < 0x0E)
                out += sprintf(out, "%d kB", (1<<(result & 0x0F))*256);
        else
                out += sprintf(out, "All");
        out += sprintf(out, "\n");
        
        return out - buf;
}

/**
 * pdcs_osdep2_read - Stable Storage OS-Dependent data area 2 output.
 * @kobj: The kobject used to share data with userspace.
 * @attr: The kobject attributes.
 * @buf: The output buffer to write to.
 *
 * This can hold pdcs_size - 224 bytes of OS-Dependent data, when available.
 */
static ssize_t pdcs_osdep2_read(struct kobject *kobj,
                                struct kobj_attribute *attr, char *buf)
{
        char *out = buf;
        unsigned long size;
        unsigned short i;
        u32 result;

        if (unlikely(pdcs_size <= 224))
                return -ENODATA;

        size = pdcs_size - 224;

        if (!buf)
                return -EINVAL;

        for (i=0; i<size; i+=4) {
                if (unlikely(pdc_stable_read(PDCS_ADDR_OSD2 + i, &result,
                                        sizeof(result)) != PDC_OK))
                        return -EIO;
                out += sprintf(out, "0x%.8x\n", result);
        }

        return out - buf;
}

/**
 * pdcs_auto_write - This function handles autoboot/search flag modifying.
 * @kobj: The kobject used to share data with userspace.
 * @attr: The kobject attributes.
 * @buf: The input buffer to read from.
 * @count: The number of bytes to be read.
 * @knob: The PF_AUTOBOOT or PF_AUTOSEARCH flag
 * 
 * We will call this function to change the current autoboot flag.
 * We expect a precise syntax:
 *      \"n\" (n == 0 or 1) to toggle AutoBoot Off or On
 */
static ssize_t pdcs_auto_write(struct kobject *kobj,
                               struct kobj_attribute *attr, const char *buf,
                               size_t count, int knob)
{
        struct pdcspath_entry *pathentry;
        unsigned char flags;
        char in[8], *temp;
        char c;

        if (!capable(CAP_SYS_ADMIN))
                return -EACCES;

        if (!buf || !count)
                return -EINVAL;

        /* We'll use a local copy of buf */
        count = min_t(size_t, count, sizeof(in)-1);
        strscpy(in, buf, count + 1);

        /* Current flags are stored in primary boot path entry */
        pathentry = &pdcspath_entry_primary;
        
        /* Be nice to the existing flag record */
        read_lock(&pathentry->rw_lock);
        flags = pathentry->devpath.path.flags;
        read_unlock(&pathentry->rw_lock);
        
        DPRINTK("%s: flags before: 0x%X\n", __func__, flags);

        temp = skip_spaces(in);

        c = *temp++ - '0';
        if ((c != 0) && (c != 1))
                goto parse_error;
        if (c == 0)
                flags &= ~knob;
        else
                flags |= knob;
        
        DPRINTK("%s: flags after: 0x%X\n", __func__, flags);
                
        /* So far so good, let's get in deep */
        write_lock(&pathentry->rw_lock);
        
        /* Change the path entry flags first */
        pathentry->devpath.path.flags = flags;
                
        /* Now, dive in. Write back to the hardware */
        pdcspath_store(pathentry);
        write_unlock(&pathentry->rw_lock);
        
        printk(KERN_INFO PDCS_PREFIX ": changed \"%s\" to \"%s\"\n",
                (knob & PF_AUTOBOOT) ? "autoboot" : "autosearch",
                (flags & knob) ? "On" : "Off");
        
        return count;

parse_error:
        printk(KERN_WARNING "%s: Parse error: expect \"n\" (n == 0 or 1)\n", __func__);
        return -EINVAL;
}

/**
 * pdcs_autoboot_write - This function handles autoboot flag modifying.
 * @kobj: The kobject used to share data with userspace.
 * @attr: The kobject attributes.
 * @buf: The input buffer to read from.
 * @count: The number of bytes to be read.
 *
 * We will call this function to change the current boot flags.
 * We expect a precise syntax:
 *      \"n\" (n == 0 or 1) to toggle AutoSearch Off or On
 */
static ssize_t pdcs_autoboot_write(struct kobject *kobj,
                                   struct kobj_attribute *attr,
                                   const char *buf, size_t count)
{
        return pdcs_auto_write(kobj, attr, buf, count, PF_AUTOBOOT);
}

/**
 * pdcs_autosearch_write - This function handles autosearch flag modifying.
 * @kobj: The kobject used to share data with userspace.
 * @attr: The kobject attributes.
 * @buf: The input buffer to read from.
 * @count: The number of bytes to be read.
 *
 * We will call this function to change the current boot flags.
 * We expect a precise syntax:
 *      \"n\" (n == 0 or 1) to toggle AutoSearch Off or On
 */
static ssize_t pdcs_autosearch_write(struct kobject *kobj,
                                     struct kobj_attribute *attr,
                                     const char *buf, size_t count)
{
        return pdcs_auto_write(kobj, attr, buf, count, PF_AUTOSEARCH);
}

/**
 * pdcs_osdep1_write - Stable Storage OS-Dependent data area 1 input.
 * @kobj: The kobject used to share data with userspace.
 * @attr: The kobject attributes.
 * @buf: The input buffer to read from.
 * @count: The number of bytes to be read.
 *
 * This can store 16 bytes of OS-Dependent data. We use a byte-by-byte
 * write approach. It's up to userspace to deal with it when constructing
 * its input buffer.
 */
static ssize_t pdcs_osdep1_write(struct kobject *kobj,
                                 struct kobj_attribute *attr,
                                 const char *buf, size_t count)
{
        u8 in[16];

        if (!capable(CAP_SYS_ADMIN))
                return -EACCES;

        if (!buf || !count)
                return -EINVAL;

        if (unlikely(pdcs_osid != OS_ID_LINUX))
                return -EPERM;

        if (count > 16)
                return -EMSGSIZE;

        /* We'll use a local copy of buf */
        memset(in, 0, 16);
        memcpy(in, buf, count);

        if (pdc_stable_write(PDCS_ADDR_OSD1, &in, sizeof(in)) != PDC_OK)
                return -EIO;

        return count;
}

/**
 * pdcs_osdep2_write - Stable Storage OS-Dependent data area 2 input.
 * @kobj: The kobject used to share data with userspace.
 * @attr: The kobject attributes.
 * @buf: The input buffer to read from.
 * @count: The number of bytes to be read.
 *
 * This can store pdcs_size - 224 bytes of OS-Dependent data. We use a
 * byte-by-byte write approach. It's up to userspace to deal with it when
 * constructing its input buffer.
 */
static ssize_t pdcs_osdep2_write(struct kobject *kobj,
                                 struct kobj_attribute *attr,
                                 const char *buf, size_t count)
{
        unsigned long size;
        unsigned short i;
        u8 in[4];

        if (!capable(CAP_SYS_ADMIN))
                return -EACCES;

        if (!buf || !count)
                return -EINVAL;

        if (unlikely(pdcs_size <= 224))
                return -ENOSYS;

        if (unlikely(pdcs_osid != OS_ID_LINUX))
                return -EPERM;

        size = pdcs_size - 224;

        if (count > size)
                return -EMSGSIZE;

        /* We'll use a local copy of buf */

        for (i=0; i<count; i+=4) {
                memset(in, 0, 4);
                memcpy(in, buf+i, (count-i < 4) ? count-i : 4);
                if (unlikely(pdc_stable_write(PDCS_ADDR_OSD2 + i, &in,
                                        sizeof(in)) != PDC_OK))
                        return -EIO;
        }

        return count;
}

/* The remaining attributes. */
static PDCS_ATTR(size, 0444, pdcs_size_read, NULL);
static PDCS_ATTR(autoboot, 0644, pdcs_autoboot_read, pdcs_autoboot_write);
static PDCS_ATTR(autosearch, 0644, pdcs_autosearch_read, pdcs_autosearch_write);
static PDCS_ATTR(timer, 0444, pdcs_timer_read, NULL);
static PDCS_ATTR(osid, 0444, pdcs_osid_read, NULL);
static PDCS_ATTR(osdep1, 0600, pdcs_osdep1_read, pdcs_osdep1_write);
static PDCS_ATTR(diagnostic, 0400, pdcs_diagnostic_read, NULL);
static PDCS_ATTR(fastsize, 0400, pdcs_fastsize_read, NULL);
static PDCS_ATTR(osdep2, 0600, pdcs_osdep2_read, pdcs_osdep2_write);

static struct attribute *pdcs_subsys_attrs[] = {
        &pdcs_attr_size.attr,
        &pdcs_attr_autoboot.attr,
        &pdcs_attr_autosearch.attr,
        &pdcs_attr_timer.attr,
        &pdcs_attr_osid.attr,
        &pdcs_attr_osdep1.attr,
        &pdcs_attr_diagnostic.attr,
        &pdcs_attr_fastsize.attr,
        &pdcs_attr_osdep2.attr,
        NULL,
};

static const struct attribute_group pdcs_attr_group = {
        .attrs = pdcs_subsys_attrs,
};

static struct kobject *stable_kobj;
static struct kset *paths_kset;

/**
 * pdcs_register_pathentries - Prepares path entries kobjects for sysfs usage.
 * 
 * It creates kobjects corresponding to each path entry with nice sysfs
 * links to the real device. This is where the magic takes place: when
 * registering the subsystem attributes during module init, each kobject hereby
 * created will show in the sysfs tree as a folder containing files as defined
 * by path_subsys_attr[].
 */
static inline int __init
pdcs_register_pathentries(void)
{
        unsigned short i;
        struct pdcspath_entry *entry;
        int err;
        
        /* Initialize the entries rw_lock before anything else */
        for (i = 0; (entry = pdcspath_entries[i]); i++)
                rwlock_init(&entry->rw_lock);

        for (i = 0; (entry = pdcspath_entries[i]); i++) {
                write_lock(&entry->rw_lock);
                err = pdcspath_fetch(entry);
                write_unlock(&entry->rw_lock);

                if (err < 0)
                        continue;

                entry->kobj.kset = paths_kset;
                err = kobject_init_and_add(&entry->kobj, &ktype_pdcspath, NULL,
                                           "%s", entry->name);
                if (err) {
                        kobject_put(&entry->kobj);
                        return err;
                }

                /* kobject is now registered */
                write_lock(&entry->rw_lock);
                entry->ready = 2;
                write_unlock(&entry->rw_lock);
                
                /* Add a nice symlink to the real device */
                if (entry->dev) {
                        err = sysfs_create_link(&entry->kobj, &entry->dev->kobj, "device");
                        WARN_ON(err);
                }

                kobject_uevent(&entry->kobj, KOBJ_ADD);
        }
        
        return 0;
}

/**
 * pdcs_unregister_pathentries - Routine called when unregistering the module.
 */
static inline void
pdcs_unregister_pathentries(void)
{
        unsigned short i;
        struct pdcspath_entry *entry;
        
        for (i = 0; (entry = pdcspath_entries[i]); i++) {
                read_lock(&entry->rw_lock);
                if (entry->ready >= 2)
                        kobject_put(&entry->kobj);
                read_unlock(&entry->rw_lock);
        }
}

/*
 * For now we register the stable subsystem with the firmware subsystem
 * and the paths subsystem with the stable subsystem
 */
static int __init
pdc_stable_init(void)
{
        int rc = 0, error;
        u32 result;

        /* find the size of the stable storage */
        if (pdc_stable_get_size(&pdcs_size) != PDC_OK) 
                return -ENODEV;

        /* make sure we have enough data */
        if (pdcs_size < 96)
                return -ENODATA;

        printk(KERN_INFO PDCS_PREFIX " facility v%s\n", PDCS_VERSION);

        /* get OSID */
        if (pdc_stable_read(PDCS_ADDR_OSID, &result, sizeof(result)) != PDC_OK)
                return -EIO;

        /* the actual result is 16 bits away */
        pdcs_osid = (u16)(result >> 16);

        /* For now we'll register the directory at /sys/firmware/stable */
        stable_kobj = kobject_create_and_add("stable", firmware_kobj);
        if (!stable_kobj) {
                rc = -ENOMEM;
                goto fail_firmreg;
        }

        /* Don't forget the root entries */
        error = sysfs_create_group(stable_kobj, &pdcs_attr_group);
        if (error) {
                rc = -ENOMEM;
                goto fail_ksetreg;
        }

        /* register the paths kset as a child of the stable kset */
        paths_kset = kset_create_and_add("paths", NULL, stable_kobj);
        if (!paths_kset) {
                rc = -ENOMEM;
                goto fail_ksetreg;
        }

        /* now we create all "files" for the paths kset */
        if ((rc = pdcs_register_pathentries()))
                goto fail_pdcsreg;

        return rc;
        
fail_pdcsreg:
        pdcs_unregister_pathentries();
        kset_unregister(paths_kset);
        
fail_ksetreg:
        kobject_put(stable_kobj);
        
fail_firmreg:
        printk(KERN_INFO PDCS_PREFIX " bailing out\n");
        return rc;
}

static void __exit
pdc_stable_exit(void)
{
        pdcs_unregister_pathentries();
        kset_unregister(paths_kset);
        kobject_put(stable_kobj);
}


module_init(pdc_stable_init);
module_exit(pdc_stable_exit);