firmware: google: memconsole: Adapt to new coreboot ring buffer format

/* CBMEM firmware console log descriptor. */

struct cbmem_cons {

	u32 buffer_size;

	u32 buffer_cursor;

	u8  buffer_body[0];

	u32 size;

	u32 cursor;

	u8  body[0];

} __packed;

#define CURSOR_MASK ((1 << 28) - 1)

#define OVERFLOW (1 << 31)

static struct cbmem_cons __iomem *cbmem_console;

/*

 * 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)

{

	return memory_read_from_buffer(buf, count, &pos,

				       cbmem_console->buffer_body,

				       min(cbmem_console->buffer_cursor,

					   cbmem_console->buffer_size));

	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)

		return -ENOMEM;

	cbmem_console = memremap(physaddr,

				 tmp_cbmc->buffer_size + sizeof(*cbmem_console),

				 tmp_cbmc->size + sizeof(*cbmem_console),

				 MEMREMAP_WB);

	memunmap(tmp_cbmc);