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/*
* memconsole-coreboot.c
*
* Memory based BIOS console accessed through coreboot table.
*
* Copyright 2017 Google Inc.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License v2.0 as published by
* the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*/
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/platform_device.h>
#include "memconsole.h"
#include "coreboot_table.h"
#define CB_TAG_CBMEM_CONSOLE 0x17
/* CBMEM firmware console log descriptor. */
struct cbmem_cons {
u32 size_dont_access_after_boot;
u32 cursor;
u8 body[0];
} __packed;
#define CURSOR_MASK ((1 << 28) - 1)
#define OVERFLOW (1 << 31)
static struct cbmem_cons __iomem *cbmem_console;
static u32 cbmem_console_size;
/*
* The cbmem_console structure is read again on every access because it may
* change at any time if runtime firmware logs new messages. This may rarely
* lead to race conditions where the firmware overwrites the beginning of the
* ring buffer with more lines after we have already read |cursor|. It should be
* rare and harmless enough that we don't spend extra effort working around it.
*/
static ssize_t memconsole_coreboot_read(char *buf, loff_t pos, size_t count)
{
u32 cursor = cbmem_console->cursor & CURSOR_MASK;
u32 flags = cbmem_console->cursor & ~CURSOR_MASK;
u32 size = cbmem_console_size;
struct seg { /* describes ring buffer segments in logical order */
u32 phys; /* physical offset from start of mem buffer */
u32 len; /* length of segment */
} seg[2] = { {0}, {0} };
size_t done = 0;
int i;
if (flags & OVERFLOW) {
if (cursor > size) /* Shouldn't really happen, but... */
cursor = 0;
seg[0] = (struct seg){.phys = cursor, .len = size - cursor};
seg[1] = (struct seg){.phys = 0, .len = cursor};
} else {
seg[0] = (struct seg){.phys = 0, .len = min(cursor, size)};
}
for (i = 0; i < ARRAY_SIZE(seg) && count > done; i++) {
done += memory_read_from_buffer(buf + done, count - done, &pos,
cbmem_console->body + seg[i].phys, seg[i].len);
pos -= seg[i].len;
}
return done;
}
static int memconsole_coreboot_init(phys_addr_t physaddr)
{
struct cbmem_cons __iomem *tmp_cbmc;
tmp_cbmc = memremap(physaddr, sizeof(*tmp_cbmc), MEMREMAP_WB);
if (!tmp_cbmc)
return -ENOMEM;
/* Read size only once to prevent overrun attack through /dev/mem. */
cbmem_console_size = tmp_cbmc->size_dont_access_after_boot;
cbmem_console = memremap(physaddr,
cbmem_console_size + sizeof(*cbmem_console),
MEMREMAP_WB);
memunmap(tmp_cbmc);
if (!cbmem_console)
return -ENOMEM;
memconsole_setup(memconsole_coreboot_read);
return 0;
}
static int memconsole_probe(struct platform_device *pdev)
{
int ret;
struct lb_cbmem_ref entry;
ret = coreboot_table_find(CB_TAG_CBMEM_CONSOLE, &entry, sizeof(entry));
if (ret)
return ret;
ret = memconsole_coreboot_init(entry.cbmem_addr);
if (ret)
return ret;
return memconsole_sysfs_init();
}
static int memconsole_remove(struct platform_device *pdev)
{
memconsole_exit();
if (cbmem_console)
memunmap(cbmem_console);
return 0;
}
static struct platform_driver memconsole_driver = {
.probe = memconsole_probe,
.remove = memconsole_remove,
.driver = {
.name = "memconsole",
},
};
static int __init platform_memconsole_init(void)
{
struct platform_device *pdev;
pdev = platform_device_register_simple("memconsole", -1, NULL, 0);
if (IS_ERR(pdev))
return PTR_ERR(pdev);
platform_driver_register(&memconsole_driver);
return 0;
}
module_init(platform_memconsole_init);
MODULE_AUTHOR("Google, Inc.");
MODULE_LICENSE("GPL");
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