// SPDX-License-Identifier: GPL-2.0

#include <linux/efi.h>
#include <linux/init.h>
#include <linux/io.h>
#include <linux/kernel.h>
#include <linux/kobject.h>
#include <linux/module.h>
#include <linux/platform_device.h>
#include <linux/sysfs.h>

#define OVMF_DEBUG_LOG_MAGIC1  0x3167646d666d766f  // "ovmfmdg1"
#define OVMF_DEBUG_LOG_MAGIC2  0x3267646d666d766f  // "ovmfmdg2"

struct ovmf_debug_log_header {
        u64    magic1;
        u64    magic2;
        u64    hdr_size;
        u64    log_size;
        u64    lock; // edk2 spinlock
        u64    head_off;
        u64    tail_off;
        u64    truncated;
        u8     fw_version[128];
};

static struct ovmf_debug_log_header *hdr;
static u8 *logbuf;
static u64 logbufsize;

static ssize_t ovmf_log_read(struct file *filp, struct kobject *kobj,
                             const struct bin_attribute *attr, char *buf,
                             loff_t offset, size_t count)
{
        u64 start, end;

        start = hdr->head_off + offset;
        if (hdr->head_off > hdr->tail_off && start >= hdr->log_size)
                start -= hdr->log_size;

        end = start + count;
        if (start > hdr->tail_off) {
                if (end > hdr->log_size)
                        end = hdr->log_size;
        } else {
                if (end > hdr->tail_off)
                        end = hdr->tail_off;
        }

        if (start > logbufsize || end > logbufsize)
                return 0;
        if (start >= end)
                return 0;

        memcpy(buf, logbuf + start, end - start);
        return end - start;
}

static struct bin_attribute ovmf_log_bin_attr = {
        .attr = {
                .name = "ovmf_debug_log",
                .mode = 0444,
        },
        .read = ovmf_log_read,
};

int __init ovmf_log_probe(unsigned long ovmf_debug_log_table)
{
        int ret = -EINVAL;
        u64 size;

        /* map + verify header */
        hdr = memremap(ovmf_debug_log_table, sizeof(*hdr), MEMREMAP_WB);
        if (!hdr) {
                pr_err("OVMF debug log: header map failed\n");
                return -EINVAL;
        }

        if (hdr->magic1 != OVMF_DEBUG_LOG_MAGIC1 ||
            hdr->magic2 != OVMF_DEBUG_LOG_MAGIC2) {
                printk(KERN_ERR "OVMF debug log: magic mismatch\n");
                goto err_unmap;
        }

        size = hdr->hdr_size + hdr->log_size;
        pr_info("OVMF debug log: firmware version: \"%s\"\n", hdr->fw_version);
        pr_info("OVMF debug log: buffer size: %lluk\n", size / 1024);

        /* map complete log buffer */
        memunmap(hdr);
        hdr = memremap(ovmf_debug_log_table, size, MEMREMAP_WB);
        if (!hdr) {
                pr_err("OVMF debug log: buffer map failed\n");
                return -EINVAL;
        }
        logbuf = (void *)hdr + hdr->hdr_size;
        logbufsize = hdr->log_size;

        ovmf_log_bin_attr.size = size;
        ret = sysfs_create_bin_file(efi_kobj, &ovmf_log_bin_attr);
        if (ret != 0) {
                pr_err("OVMF debug log: sysfs register failed\n");
                goto err_unmap;
        }

        return 0;

err_unmap:
        memunmap(hdr);
        return ret;
}