x86: coreboot: Document cbmem console struct

Coreboot changed a few years ago to include an overflow flag. Update the
structure to match this.

This comes from coreboot commit:

   6f5ead14b4 ("mb/google/nissa/var/joxer: Update eMMC DLL settings")

Note: There are several implementations of this in coreboot. I have chosen
to follow the one in src/lib/cbmem_console.c

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>

1 files changed, 15 insertions, 2 deletions

diff --git a/arch/x86/include/asm/coreboot_tables.h b/arch/x86/include/asm/coreboot_tables.h
index 4de137f..0dfb64b 100644
--- a/arch/x86/include/asm/coreboot_tables.h
+++ b/arch/x86/include/asm/coreboot_tables.h
@@ -299,11 +299,24 @@ struct cb_vdat {
 #define CB_TAG_TIMESTAMPS		0x0016
 #define CB_TAG_CBMEM_CONSOLE		0x0017
 
+#define CBMC_CURSOR_MASK	((1 << 28) - 1)
+#define CBMC_OVERFLOW		BIT(31)
+
+/*
+ * struct cbmem_console - In-memory console buffer for coreboot
+ *
+ * Structure describing console buffer. It is overlaid on a flat memory area,
+ * with body covering the extent of the memory. Once the buffer is full,
+ * output will wrap back around to the start of the buffer. The high bit of the
+ * cursor field gets set to indicate that this happened. If the underlying
+ * storage allows this, the buffer will persist across multiple boots and append
+ * to the previous log.
+ */
 struct cbmem_console {
 	u32 size;
 	u32 cursor;
-	char body[0];
-} __packed;
+	u8  body[0];
+};
 
 #define CB_TAG_MRC_CACHE		0x0018