111 lines
2.9 KiB
C
111 lines
2.9 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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* memconsole-coreboot.c
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*
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* Memory based BIOS console accessed through coreboot table.
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*
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* Copyright 2017 Google Inc.
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*/
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#include <linux/device.h>
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#include <linux/io.h>
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#include <linux/kernel.h>
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#include <linux/module.h>
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#include "memconsole.h"
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#include "coreboot_table.h"
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#define CB_TAG_CBMEM_CONSOLE 0x17
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/* CBMEM firmware console log descriptor. */
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struct cbmem_cons {
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u32 size_dont_access_after_boot;
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u32 cursor;
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u8 body[];
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} __packed;
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#define CURSOR_MASK ((1 << 28) - 1)
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#define OVERFLOW (1 << 31)
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static struct cbmem_cons *cbmem_console;
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static u32 cbmem_console_size;
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/*
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* The cbmem_console structure is read again on every access because it may
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* change at any time if runtime firmware logs new messages. This may rarely
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* lead to race conditions where the firmware overwrites the beginning of the
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* ring buffer with more lines after we have already read |cursor|. It should be
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* rare and harmless enough that we don't spend extra effort working around it.
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*/
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static ssize_t memconsole_coreboot_read(char *buf, loff_t pos, size_t count)
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{
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u32 cursor = cbmem_console->cursor & CURSOR_MASK;
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u32 flags = cbmem_console->cursor & ~CURSOR_MASK;
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u32 size = cbmem_console_size;
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struct seg { /* describes ring buffer segments in logical order */
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u32 phys; /* physical offset from start of mem buffer */
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u32 len; /* length of segment */
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} seg[2] = { {0}, {0} };
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size_t done = 0;
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int i;
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if (flags & OVERFLOW) {
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if (cursor > size) /* Shouldn't really happen, but... */
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cursor = 0;
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seg[0] = (struct seg){.phys = cursor, .len = size - cursor};
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seg[1] = (struct seg){.phys = 0, .len = cursor};
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} else {
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seg[0] = (struct seg){.phys = 0, .len = min(cursor, size)};
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}
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for (i = 0; i < ARRAY_SIZE(seg) && count > done; i++) {
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done += memory_read_from_buffer(buf + done, count - done, &pos,
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cbmem_console->body + seg[i].phys, seg[i].len);
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pos -= seg[i].len;
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}
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return done;
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}
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static int memconsole_probe(struct coreboot_device *dev)
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{
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struct cbmem_cons *tmp_cbmc;
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tmp_cbmc = memremap(dev->cbmem_ref.cbmem_addr,
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sizeof(*tmp_cbmc), MEMREMAP_WB);
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if (!tmp_cbmc)
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return -ENOMEM;
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/* Read size only once to prevent overrun attack through /dev/mem. */
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cbmem_console_size = tmp_cbmc->size_dont_access_after_boot;
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cbmem_console = devm_memremap(&dev->dev, dev->cbmem_ref.cbmem_addr,
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cbmem_console_size + sizeof(*cbmem_console),
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MEMREMAP_WB);
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memunmap(tmp_cbmc);
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if (IS_ERR(cbmem_console))
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return PTR_ERR(cbmem_console);
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memconsole_setup(memconsole_coreboot_read);
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return memconsole_sysfs_init();
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}
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static void memconsole_remove(struct coreboot_device *dev)
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{
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memconsole_exit();
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}
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static struct coreboot_driver memconsole_driver = {
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.probe = memconsole_probe,
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.remove = memconsole_remove,
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.drv = {
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.name = "memconsole",
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},
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.tag = CB_TAG_CBMEM_CONSOLE,
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};
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module_coreboot_driver(memconsole_driver);
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MODULE_AUTHOR("Google, Inc.");
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MODULE_LICENSE("GPL");
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