console: Add compile-time fast path when only CBMEM console is used

A common use case when running coreboot on production systems is that
only the CBMEM console (the one with the least impact on boot speed) is
enabled. In this case, some of the code in the console subsystem has no
effect. Due to the way it's all genericized over multiple consoles and
tied together with function pointers, not all of this can be
compile-time eliminated automatically, so this patch adds a little
helper to facilitate that. This results in roughly 200 (compressed)
bytes of savings per stage on an arm64 system.

Signed-off-by: Julius Werner <jwerner@chromium.org>
Change-Id: I1d5b8bda80d02a13ee0b7835e0805c4319fd21d8
Reviewed-on: https://review.coreboot.org/c/coreboot/+/61613
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Raul Rangel <rrangel@chromium.org>

3 files changed, 19 insertions, 4 deletions

diff --git a/src/console/console.c b/src/console/console.c
index 5b8a872e0e..f37f120f82 100644
--- a/src/console/console.c
+++ b/src/console/console.c
@@ -11,6 +11,8 @@
 #include <console/flash.h>
 #include <console/system76_ec.h>
 
+/* Note: when adding a new console, make sure you update the definition of
+   HAS_ONLY_FAST_CONSOLES in <console.h>! */
 void console_hw_init(void)
 {
 	__cbmemc_init();
diff --git a/src/console/printk.c b/src/console/printk.c
index ffa3106178..8db2c45f13 100644
--- a/src/console/printk.c
+++ b/src/console/printk.c
@@ -67,6 +67,8 @@ union log_state {
 	};
 };
 
+#define LOG_FAST(state) (HAS_ONLY_FAST_CONSOLES || ((state).level == CONSOLE_LOG_FAST))
+
 static void wrap_interactive_printf(const char *fmt, ...)
 {
 	va_list args;
@@ -83,7 +85,7 @@ static void line_start(union log_state state)
 	   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) {
+	if (LOG_FAST(state)) {
 		__cbmemc_tx_byte(marker);
 		return;
 	}
@@ -98,7 +100,7 @@ static void line_start(union log_state state)
 
 static void line_end(union log_state state)
 {
-	if (CONFIG(CONSOLE_USE_ANSI_ESCAPES) && state.speed != CONSOLE_LOG_FAST)
+	if (CONFIG(CONSOLE_USE_ANSI_ESCAPES) && !LOG_FAST(state))
 		wrap_interactive_printf(BIOS_LOG_ESCAPE_RESET);
 }
 
@@ -115,7 +117,7 @@ static void wrap_putchar(unsigned char byte, void *data)
 		line_started = true;
 	}
 
-	if (state.speed == CONSOLE_LOG_FAST)
+	if (LOG_FAST(state))
 		__cbmemc_tx_byte(byte);
 	else
 		console_tx_byte(byte);
@@ -138,7 +140,7 @@ int vprintk(int msg_level, const char *fmt, va_list args)
 	console_time_run();
 
 	i = vtxprintf(wrap_putchar, fmt, args, state.as_ptr);
-	if (state.speed != CONSOLE_LOG_FAST)
+	if (LOG_FAST(state))
 		console_tx_flush();
 
 	console_time_stop();
diff --git a/src/include/console/console.h b/src/include/console/console.h
index 5546aa98e5..e4090af48b 100644
--- a/src/include/console/console.h
+++ b/src/include/console/console.h
@@ -61,7 +61,18 @@ void do_putchar(unsigned char byte);
 long console_time_get_and_reset(void);
 void console_time_report(void);
 
+/*
+ * "Fast" basically means only the CBMEM console right now. This is used to still
+ * print debug messages there when loglevel disables the other consoles. It is also
+ * used to compile-time eliminate code paths that only affect "interactive" consoles
+ * (which are all "slow") when none of those are enabled.
+ */
 enum { CONSOLE_LOG_NONE = 0, CONSOLE_LOG_FAST, CONSOLE_LOG_ALL };
+#define HAS_ONLY_FAST_CONSOLES !(CONFIG(SPKMODEM) || CONFIG(CONSOLE_QEMU_DEBUGCON) || \
+	CONFIG(CONSOLE_SERIAL) || CONFIG(CONSOLE_NE2K) || CONFIG(CONSOLE_USB) || \
+	CONFIG(EM100PRO_SPI_CONSOLE) || CONFIG(CONSOLE_SPI_FLASH) || \
+	CONFIG(CONSOLE_SYSTEM76_EC))
+
 #else
 static inline int get_log_level(void) { return -1; }
 static inline void console_init(void) {}