console: Add loglevel marker codes to stored consoles

In order to provide the same loglevel prefixes and highlighting that
were recently introduced for "interactive" consoles (e.g. UART) to
"stored" consoles (e.g. CBMEM) but minimize the amont of extra storage
space wasted on this info, this patch will write a 1-byte control
character marker indicating the loglevel to the start of every line
logged in those consoles. The `cbmem` utility will then interpret those
markers and translate them back into loglevel prefixes and escape
sequences as needed.

Since coreboot and userspace log readers aren't always in sync,
occasionally an older reader may come across these markers and not know
how to interpret them... but that should usually be fine, as the range
chosen contains non-printable ASCII characters that normally have no
effect on the terminal. At worst the outdated reader would display one
garbled character at the start of every line which isn't that bad.
(Older versions of the `cbmem` utility will translate non-printable
characters into `?` question marks.)

Signed-off-by: Julius Werner <jwerner@chromium.org>
Change-Id: I86073f48aaf1e0a58e97676fb80e2475ec418ffc
Reviewed-on: https://review.coreboot.org/c/coreboot/+/61308
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Raul Rangel <rrangel@chromium.org>

1 files changed, 9 insertions, 1 deletions

diff --git a/src/console/printk.c b/src/console/printk.c
index 93aed52377..ffa3106178 100644
--- a/src/console/printk.c
+++ b/src/console/printk.c
@@ -78,8 +78,16 @@ static void line_start(union log_state state)
 {
 	if (state.level > BIOS_LOG_PREFIX_MAX_LEVEL)
 		return;
-	if (state.speed == CONSOLE_LOG_FAST)
+
+	/* Stored consoles just get a single control char marker to save space. If we are in
+	   LOG_FAST mode, just write the marker to CBMC and exit -- the rest of this function
+	   implements the LOG_ALL case. */
+	unsigned char marker = BIOS_LOG_LEVEL_TO_MARKER(state.level);
+	if (state.speed == CONSOLE_LOG_FAST) {
+		__cbmemc_tx_byte(marker);
 		return;
+	}
+	console_stored_tx_byte(marker, NULL);
 
 	/* Interactive consoles get a `[DEBUG]  ` style readable prefix,
 	   and potentially an escape sequence for highlighting. */