// SPDX-License-Identifier: GPL-2.0+
/*
 * Copyright 2019 Google Inc
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version
 * 2 of the License, or (at your option) any later version.
 *
 * Provides a simple driver to control the ASPEED P2A interface which allows
 * the host to read and write to various regions of the BMC's memory.
 */

#include <linux/fs.h>
#include <linux/io.h>
#include <linux/mfd/syscon.h>
#include <linux/miscdevice.h>
#include <linux/mm.h>
#include <linux/module.h>
#include <linux/mutex.h>
#include <linux/of.h>
#include <linux/of_reserved_mem.h>
#include <linux/platform_device.h>
#include <linux/regmap.h>
#include <linux/slab.h>
#include <linux/uaccess.h>

#include <linux/aspeed-p2a-ctrl.h>

#define DEVICE_NAME     "aspeed-p2a-ctrl"

/* SCU2C is a Misc. Control Register. */
#define SCU2C 0x2c
/* SCU180 is the PCIe Configuration Setting Control Register. */
#define SCU180 0x180
/* Bit 1 controls the P2A bridge, while bit 0 controls the entire VGA device
 * on the PCI bus.
 */
#define SCU180_ENP2A BIT(1)

/* The ast2400/2500 both have six ranges. */
#define P2A_REGION_COUNT 6

struct region {
        u64 min;
        u64 max;
        u32 bit;
};

struct aspeed_p2a_model_data {
        /* min, max, bit */
        struct region regions[P2A_REGION_COUNT];
};

struct aspeed_p2a_ctrl {
        struct miscdevice miscdev;
        struct regmap *regmap;

        const struct aspeed_p2a_model_data *config;

        /* Access to these needs to be locked, held via probe, mapping ioctl,
         * and release, remove.
         */
        struct mutex tracking;
        u32 readers;
        u32 readerwriters[P2A_REGION_COUNT];

        phys_addr_t mem_base;
        resource_size_t mem_size;
};

struct aspeed_p2a_user {
        struct file *file;
        struct aspeed_p2a_ctrl *parent;

        /* The entire memory space is opened for reading once the bridge is
         * enabled, therefore this needs only to be tracked once per user.
         * If any user has it open for read, the bridge must stay enabled.
         */
        u32 read;

        /* Each entry of the array corresponds to a P2A Region.  If the user
         * opens for read or readwrite, the reference goes up here.  On
         * release, this array is walked and references adjusted accordingly.
         */
        u32 readwrite[P2A_REGION_COUNT];
};

static void aspeed_p2a_enable_bridge(struct aspeed_p2a_ctrl *p2a_ctrl)
{
        regmap_update_bits(p2a_ctrl->regmap,
                SCU180, SCU180_ENP2A, SCU180_ENP2A);
}

static void aspeed_p2a_disable_bridge(struct aspeed_p2a_ctrl *p2a_ctrl)
{
        regmap_update_bits(p2a_ctrl->regmap, SCU180, SCU180_ENP2A, 0);
}

static int aspeed_p2a_mmap(struct file *file, struct vm_area_struct *vma)
{
        unsigned long vsize;
        pgprot_t prot;
        struct aspeed_p2a_user *priv = file->private_data;
        struct aspeed_p2a_ctrl *ctrl = priv->parent;

        if (ctrl->mem_base == 0 && ctrl->mem_size == 0)
                return -EINVAL;

        vsize = vma->vm_end - vma->vm_start;
        prot = vma->vm_page_prot;

        if (vma->vm_pgoff + vma_pages(vma) > ctrl->mem_size >> PAGE_SHIFT)
                return -EINVAL;

        /* ast2400/2500 AHB accesses are not cache coherent */
        prot = pgprot_noncached(prot);

        if (remap_pfn_range(vma, vma->vm_start,
                (ctrl->mem_base >> PAGE_SHIFT) + vma->vm_pgoff,
                vsize, prot))
                return -EAGAIN;

        return 0;
}

static bool aspeed_p2a_region_acquire(struct aspeed_p2a_user *priv,
                struct aspeed_p2a_ctrl *ctrl,
                struct aspeed_p2a_ctrl_mapping *map)
{
        int i;
        u64 base, end;
        bool matched = false;

        base = map->addr;
        end = map->addr + (map->length - 1);

        /* If the value is a legal u32, it will find a match. */
        for (i = 0; i < P2A_REGION_COUNT; i++) {
                const struct region *curr = &ctrl->config->regions[i];

                /* If the top of this region is lower than your base, skip it.
                 */
                if (curr->max < base)
                        continue;

                /* If the bottom of this region is higher than your end, bail.
                 */
                if (curr->min > end)
                        break;

                /* Lock this and update it, therefore it someone else is
                 * closing their file out, this'll preserve the increment.
                 */
                mutex_lock(&ctrl->tracking);
                ctrl->readerwriters[i] += 1;
                mutex_unlock(&ctrl->tracking);

                /* Track with the user, so when they close their file, we can
                 * decrement properly.
                 */
                priv->readwrite[i] += 1;

                /* Enable the region as read-write. */
                regmap_update_bits(ctrl->regmap, SCU2C, curr->bit, 0);
                matched = true;
        }

        return matched;
}

static long aspeed_p2a_ioctl(struct file *file, unsigned int cmd,
                unsigned long data)
{
        struct aspeed_p2a_user *priv = file->private_data;
        struct aspeed_p2a_ctrl *ctrl = priv->parent;
        void __user *arg = (void __user *)data;
        struct aspeed_p2a_ctrl_mapping map;

        if (copy_from_user(&map, arg, sizeof(map)))
                return -EFAULT;

        switch (cmd) {
        case ASPEED_P2A_CTRL_IOCTL_SET_WINDOW:
                /* If they want a region to be read-only, since the entire
                 * region is read-only once enabled, we just need to track this
                 * user wants to read from the bridge, and if it's not enabled.
                 * Enable it.
                 */
                if (map.flags == ASPEED_P2A_CTRL_READ_ONLY) {
                        mutex_lock(&ctrl->tracking);
                        ctrl->readers += 1;
                        mutex_unlock(&ctrl->tracking);

                        /* Track with the user, so when they close their file,
                         * we can decrement properly.
                         */
                        priv->read += 1;
                } else if (map.flags == ASPEED_P2A_CTRL_READWRITE) {
                        /* If we don't acquire any region return error. */
                        if (!aspeed_p2a_region_acquire(priv, ctrl, &map)) {
                                return -EINVAL;
                        }
                } else {
                        /* Invalid map flags. */
                        return -EINVAL;
                }

                aspeed_p2a_enable_bridge(ctrl);
                return 0;
        case ASPEED_P2A_CTRL_IOCTL_GET_MEMORY_CONFIG:
                /* This is a request for the memory-region and corresponding
                 * length that is used by the driver for mmap.
                 */

                map.flags = 0;
                map.addr = ctrl->mem_base;
                map.length = ctrl->mem_size;

                return copy_to_user(arg, &map, sizeof(map)) ? -EFAULT : 0;
        }

        return -EINVAL;
}


/*
 * When a user opens this file, we create a structure to track their mappings.
 *
 * A user can map a region as read-only (bridge enabled), or read-write (bit
 * flipped, and bridge enabled).  Either way, this tracking is used, s.t. when
 * they release the device references are handled.
 *
 * The bridge is not enabled until a user calls an ioctl to map a region,
 * simply opening the device does not enable it.
 */
static int aspeed_p2a_open(struct inode *inode, struct file *file)
{
        struct aspeed_p2a_user *priv;

        priv = kmalloc_obj(*priv);
        if (!priv)
                return -ENOMEM;

        priv->file = file;
        priv->read = 0;
        memset(priv->readwrite, 0, sizeof(priv->readwrite));

        /* The file's private_data is initialized to the p2a_ctrl. */
        priv->parent = file->private_data;

        /* Set the file's private_data to the user's data. */
        file->private_data = priv;

        return 0;
}

/*
 * This will close the users mappings.  It will go through what they had opened
 * for readwrite, and decrement those counts.  If at the end, this is the last
 * user, it'll close the bridge.
 */
static int aspeed_p2a_release(struct inode *inode, struct file *file)
{
        int i;
        u32 bits = 0;
        bool open_regions = false;
        struct aspeed_p2a_user *priv = file->private_data;

        /* Lock others from changing these values until everything is updated
         * in one pass.
         */
        mutex_lock(&priv->parent->tracking);

        priv->parent->readers -= priv->read;

        for (i = 0; i < P2A_REGION_COUNT; i++) {
                priv->parent->readerwriters[i] -= priv->readwrite[i];

                if (priv->parent->readerwriters[i] > 0)
                        open_regions = true;
                else
                        bits |= priv->parent->config->regions[i].bit;
        }

        /* Setting a bit to 1 disables the region, so let's just OR with the
         * above to disable any.
         */

        /* Note, if another user is trying to ioctl, they can't grab tracking,
         * and therefore can't grab either register mutex.
         * If another user is trying to close, they can't grab tracking either.
         */
        regmap_update_bits(priv->parent->regmap, SCU2C, bits, bits);

        /* If parent->readers is zero and open windows is 0, disable the
         * bridge.
         */
        if (!open_regions && priv->parent->readers == 0)
                aspeed_p2a_disable_bridge(priv->parent);

        mutex_unlock(&priv->parent->tracking);

        kfree(priv);

        return 0;
}

static const struct file_operations aspeed_p2a_ctrl_fops = {
        .owner = THIS_MODULE,
        .mmap = aspeed_p2a_mmap,
        .unlocked_ioctl = aspeed_p2a_ioctl,
        .open = aspeed_p2a_open,
        .release = aspeed_p2a_release,
};

/* The regions are controlled by SCU2C */
static void aspeed_p2a_disable_all(struct aspeed_p2a_ctrl *p2a_ctrl)
{
        int i;
        u32 value = 0;

        for (i = 0; i < P2A_REGION_COUNT; i++)
                value |= p2a_ctrl->config->regions[i].bit;

        regmap_update_bits(p2a_ctrl->regmap, SCU2C, value, value);

        /* Disable the bridge. */
        aspeed_p2a_disable_bridge(p2a_ctrl);
}

static int aspeed_p2a_ctrl_probe(struct platform_device *pdev)
{
        struct aspeed_p2a_ctrl *misc_ctrl;
        struct device *dev;
        struct resource resm;
        int rc = 0;

        dev = &pdev->dev;

        misc_ctrl = devm_kzalloc(dev, sizeof(*misc_ctrl), GFP_KERNEL);
        if (!misc_ctrl)
                return -ENOMEM;

        mutex_init(&misc_ctrl->tracking);

        /* optional. */
        rc = of_reserved_mem_region_to_resource(dev->of_node, 0, &resm);
        if (!rc) {
                misc_ctrl->mem_size = resource_size(&resm);
                misc_ctrl->mem_base = resm.start;
        }

        misc_ctrl->regmap = syscon_node_to_regmap(pdev->dev.parent->of_node);
        if (IS_ERR(misc_ctrl->regmap)) {
                dev_err(dev, "Couldn't get regmap\n");
                return -ENODEV;
        }

        misc_ctrl->config = of_device_get_match_data(dev);

        dev_set_drvdata(&pdev->dev, misc_ctrl);

        aspeed_p2a_disable_all(misc_ctrl);

        misc_ctrl->miscdev.minor = MISC_DYNAMIC_MINOR;
        misc_ctrl->miscdev.name = DEVICE_NAME;
        misc_ctrl->miscdev.fops = &aspeed_p2a_ctrl_fops;
        misc_ctrl->miscdev.parent = dev;

        rc = misc_register(&misc_ctrl->miscdev);
        if (rc)
                dev_err(dev, "Unable to register device\n");

        return rc;
}

static void aspeed_p2a_ctrl_remove(struct platform_device *pdev)
{
        struct aspeed_p2a_ctrl *p2a_ctrl = dev_get_drvdata(&pdev->dev);

        misc_deregister(&p2a_ctrl->miscdev);
}

#define SCU2C_DRAM      BIT(25)
#define SCU2C_SPI       BIT(24)
#define SCU2C_SOC       BIT(23)
#define SCU2C_FLASH     BIT(22)

static const struct aspeed_p2a_model_data ast2400_model_data = {
        .regions = {
                {0x00000000, 0x17FFFFFF, SCU2C_FLASH},
                {0x18000000, 0x1FFFFFFF, SCU2C_SOC},
                {0x20000000, 0x2FFFFFFF, SCU2C_FLASH},
                {0x30000000, 0x3FFFFFFF, SCU2C_SPI},
                {0x40000000, 0x5FFFFFFF, SCU2C_DRAM},
                {0x60000000, 0xFFFFFFFF, SCU2C_SOC},
        }
};

static const struct aspeed_p2a_model_data ast2500_model_data = {
        .regions = {
                {0x00000000, 0x0FFFFFFF, SCU2C_FLASH},
                {0x10000000, 0x1FFFFFFF, SCU2C_SOC},
                {0x20000000, 0x3FFFFFFF, SCU2C_FLASH},
                {0x40000000, 0x5FFFFFFF, SCU2C_SOC},
                {0x60000000, 0x7FFFFFFF, SCU2C_SPI},
                {0x80000000, 0xFFFFFFFF, SCU2C_DRAM},
        }
};

static const struct of_device_id aspeed_p2a_ctrl_match[] = {
        { .compatible = "aspeed,ast2400-p2a-ctrl",
          .data = &ast2400_model_data },
        { .compatible = "aspeed,ast2500-p2a-ctrl",
          .data = &ast2500_model_data },
        { },
};

static struct platform_driver aspeed_p2a_ctrl_driver = {
        .driver = {
                .name           = DEVICE_NAME,
                .of_match_table = aspeed_p2a_ctrl_match,
        },
        .probe = aspeed_p2a_ctrl_probe,
        .remove = aspeed_p2a_ctrl_remove,
};

module_platform_driver(aspeed_p2a_ctrl_driver);

MODULE_DEVICE_TABLE(of, aspeed_p2a_ctrl_match);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Patrick Venture <venture@google.com>");
MODULE_DESCRIPTION("Control for aspeed 2400/2500 P2A VGA HOST to BMC mappings");