// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * AMD Node helper functions and common defines
 *
 * Copyright (c) 2024, Advanced Micro Devices, Inc.
 * All Rights Reserved.
 *
 * Author: Yazen Ghannam <Yazen.Ghannam@amd.com>
 */

#include <linux/debugfs.h>
#include <asm/amd/node.h>

/*
 * AMD Nodes are a physical collection of I/O devices within an SoC. There can be one
 * or more nodes per package.
 *
 * The nodes are software-visible through PCI config space. All nodes are enumerated
 * on segment 0 bus 0. The device (slot) numbers range from 0x18 to 0x1F (maximum 8
 * nodes) with 0x18 corresponding to node 0, 0x19 to node 1, etc. Each node can be a
 * multi-function device.
 *
 * On legacy systems, these node devices represent integrated Northbridge functionality.
 * On Zen-based systems, these node devices represent Data Fabric functionality.
 *
 * See "Configuration Space Accesses" section in BKDGs or
 * "Processor x86 Core" -> "Configuration Space" section in PPRs.
 */
struct pci_dev *amd_node_get_func(u16 node, u8 func)
{
        if (node >= MAX_AMD_NUM_NODES)
                return NULL;

        return pci_get_domain_bus_and_slot(0, 0, PCI_DEVFN(AMD_NODE0_PCI_SLOT + node, func));
}

static struct pci_dev **amd_roots;

/* Protect the PCI config register pairs used for SMN. */
static DEFINE_MUTEX(smn_mutex);
static bool smn_exclusive;

#define SMN_INDEX_OFFSET        0x60
#define SMN_DATA_OFFSET         0x64

#define HSMP_INDEX_OFFSET       0xc4
#define HSMP_DATA_OFFSET        0xc8

/*
 * SMN accesses may fail in ways that are difficult to detect here in the called
 * functions amd_smn_read() and amd_smn_write(). Therefore, callers must do
 * their own checking based on what behavior they expect.
 *
 * For SMN reads, the returned value may be zero if the register is Read-as-Zero.
 * Or it may be a "PCI Error Response", e.g. all 0xFFs. The "PCI Error Response"
 * can be checked here, and a proper error code can be returned.
 *
 * But the Read-as-Zero response cannot be verified here. A value of 0 may be
 * correct in some cases, so callers must check that this correct is for the
 * register/fields they need.
 *
 * For SMN writes, success can be determined through a "write and read back"
 * However, this is not robust when done here.
 *
 * Possible issues:
 *
 * 1) Bits that are "Write-1-to-Clear". In this case, the read value should
 *    *not* match the write value.
 *
 * 2) Bits that are "Read-as-Zero"/"Writes-Ignored". This information cannot be
 *    known here.
 *
 * 3) Bits that are "Reserved / Set to 1". Ditto above.
 *
 * Callers of amd_smn_write() should do the "write and read back" check
 * themselves, if needed.
 *
 * For #1, they can see if their target bits got cleared.
 *
 * For #2 and #3, they can check if their target bits got set as intended.
 *
 * This matches what is done for RDMSR/WRMSR. As long as there's no #GP, then
 * the operation is considered a success, and the caller does their own
 * checking.
 */
static int __amd_smn_rw(u8 i_off, u8 d_off, u16 node, u32 address, u32 *value, bool write)
{
        struct pci_dev *root;
        int err = -ENODEV;

        if (node >= amd_num_nodes())
                return err;

        root = amd_roots[node];
        if (!root)
                return err;

        if (!smn_exclusive)
                return err;

        guard(mutex)(&smn_mutex);

        err = pci_write_config_dword(root, i_off, address);
        if (err) {
                pr_warn("Error programming SMN address 0x%x.\n", address);
                return pcibios_err_to_errno(err);
        }

        err = (write ? pci_write_config_dword(root, d_off, *value)
                     : pci_read_config_dword(root, d_off, value));

        return pcibios_err_to_errno(err);
}

int __must_check amd_smn_read(u16 node, u32 address, u32 *value)
{
        int err = __amd_smn_rw(SMN_INDEX_OFFSET, SMN_DATA_OFFSET, node, address, value, false);

        if (PCI_POSSIBLE_ERROR(*value)) {
                err = -ENODEV;
                *value = 0;
        }

        return err;
}
EXPORT_SYMBOL_GPL(amd_smn_read);

int __must_check amd_smn_write(u16 node, u32 address, u32 value)
{
        return __amd_smn_rw(SMN_INDEX_OFFSET, SMN_DATA_OFFSET, node, address, &value, true);
}
EXPORT_SYMBOL_GPL(amd_smn_write);

int __must_check amd_smn_hsmp_rdwr(u16 node, u32 address, u32 *value, bool write)
{
        return __amd_smn_rw(HSMP_INDEX_OFFSET, HSMP_DATA_OFFSET, node, address, value, write);
}
EXPORT_SYMBOL_GPL(amd_smn_hsmp_rdwr);

static struct dentry *debugfs_dir;
static u16 debug_node;
static u32 debug_address;

static ssize_t smn_node_write(struct file *file, const char __user *userbuf,
                              size_t count, loff_t *ppos)
{
        u16 node;
        int ret;

        ret = kstrtou16_from_user(userbuf, count, 0, &node);
        if (ret)
                return ret;

        if (node >= amd_num_nodes())
                return -ENODEV;

        debug_node = node;
        return count;
}

static int smn_node_show(struct seq_file *m, void *v)
{
        seq_printf(m, "0x%08x\n", debug_node);
        return 0;
}

static ssize_t smn_address_write(struct file *file, const char __user *userbuf,
                                 size_t count, loff_t *ppos)
{
        int ret;

        ret = kstrtouint_from_user(userbuf, count, 0, &debug_address);
        if (ret)
                return ret;

        return count;
}

static int smn_address_show(struct seq_file *m, void *v)
{
        seq_printf(m, "0x%08x\n", debug_address);
        return 0;
}

static int smn_value_show(struct seq_file *m, void *v)
{
        u32 val;
        int ret;

        ret = amd_smn_read(debug_node, debug_address, &val);
        if (ret)
                return ret;

        seq_printf(m, "0x%08x\n", val);
        return 0;
}

static ssize_t smn_value_write(struct file *file, const char __user *userbuf,
                               size_t count, loff_t *ppos)
{
        u32 val;
        int ret;

        ret = kstrtouint_from_user(userbuf, count, 0, &val);
        if (ret)
                return ret;

        add_taint(TAINT_CPU_OUT_OF_SPEC, LOCKDEP_STILL_OK);

        ret = amd_smn_write(debug_node, debug_address, val);
        if (ret)
                return ret;

        return count;
}

DEFINE_SHOW_STORE_ATTRIBUTE(smn_node);
DEFINE_SHOW_STORE_ATTRIBUTE(smn_address);
DEFINE_SHOW_STORE_ATTRIBUTE(smn_value);

static struct pci_dev *get_next_root(struct pci_dev *root)
{
        while ((root = pci_get_class(PCI_CLASS_BRIDGE_HOST << 8, root))) {
                /* Root device is Device 0 Function 0. */
                if (root->devfn)
                        continue;

                if (root->vendor != PCI_VENDOR_ID_AMD &&
                    root->vendor != PCI_VENDOR_ID_HYGON)
                        continue;

                break;
        }

        return root;
}

static bool enable_dfs;

static int __init amd_smn_enable_dfs(char *str)
{
        enable_dfs = true;
        return 1;
}
__setup("amd_smn_debugfs_enable", amd_smn_enable_dfs);

static int __init amd_smn_init(void)
{
        u16 count, num_roots, roots_per_node, node, num_nodes;
        struct pci_dev *root;

        if (!cpu_feature_enabled(X86_FEATURE_ZEN))
                return 0;

        guard(mutex)(&smn_mutex);

        if (amd_roots)
                return 0;

        num_roots = 0;
        root = NULL;
        while ((root = get_next_root(root))) {
                pci_dbg(root, "Reserving PCI config space\n");

                /*
                 * There are a few SMN index/data pairs and other registers
                 * that shouldn't be accessed by user space. So reserve the
                 * entire PCI config space for simplicity rather than covering
                 * specific registers piecemeal.
                 */
                if (!pci_request_config_region_exclusive(root, 0, PCI_CFG_SPACE_SIZE, NULL)) {
                        pci_err(root, "Failed to reserve config space\n");
                        return -EEXIST;
                }

                num_roots++;
        }

        pr_debug("Found %d AMD root devices\n", num_roots);

        if (!num_roots)
                return -ENODEV;

        num_nodes = amd_num_nodes();
        amd_roots = kzalloc_objs(*amd_roots, num_nodes);
        if (!amd_roots)
                return -ENOMEM;

        roots_per_node = num_roots / num_nodes;

        count = 0;
        node = 0;
        root = NULL;
        while (node < num_nodes && (root = get_next_root(root))) {
                /* Use one root for each node and skip the rest. */
                if (count++ % roots_per_node)
                        continue;

                pci_dbg(root, "is root for AMD node %u\n", node);
                amd_roots[node++] = root;
        }

        if (enable_dfs) {
                debugfs_dir = debugfs_create_dir("amd_smn", arch_debugfs_dir);

                debugfs_create_file("node",     0600, debugfs_dir, NULL, &smn_node_fops);
                debugfs_create_file("address",  0600, debugfs_dir, NULL, &smn_address_fops);
                debugfs_create_file("value",    0600, debugfs_dir, NULL, &smn_value_fops);
        }

        smn_exclusive = true;

        return 0;
}

fs_initcall(amd_smn_init);