[U-Boot] [PATCH v2] Add board_panic_no_console to deal with early critical errors

[Simon Glass]

This patch adds support for calling panic() before stdio is initialized.
At present this will just hang with little or no indication of what the
problem is.

A new board_panic_no_console() function is added to the board API. If provided
by the board it will be called in the event of a panic before the console is
ready. This function should turn on all UARTS and spray the message out if
it possibly can.

The feature is controlled by a new CONFIG_PRE_CONSOLE_PANIC option.

Signed-off-by: Simon Glass <sjg at chromium.org>
---
Changes in v2:
- Made this feature conditional on CONFIG_PRE_CONSOLE_PANIC

 README           |   11 +++++++++++
 include/common.h |    8 ++++++++
 lib/vsprintf.c   |   29 +++++++++++++++++++++++++++++
 3 files changed, 48 insertions(+), 0 deletions(-)

diff --git a/README b/README
index eb9ade9..0748a6f 100644
--- a/README
+++ b/README
@@ -634,6 +634,17 @@ The following options need to be configured:
 		'Sane' compilers will generate smaller code if
 		CONFIG_PRE_CON_BUF_SZ is a power of 2
 
+- Pre-console Panic:
+		Prior to the console being initialised, since console output
+		is silently discarded, a panic() will cause no output and no
+		indication of what is wrong. However, if the
+		CONFIG_PRE_CONSOLE_PANIC option is defined, then U-Boot will
+		call board_panic_no_console() in this case, passing the panic
+		message. This function should try to output the message if
+		possible, perhaps on all available UARTs (it will need to do
+		this directly, since the console code is not functional yet).
+		Another option is to flash some LEDs to indicate a panic.
+
 - Boot Delay:	CONFIG_BOOTDELAY - in seconds
 		Delay before automatically booting the default image;
 		set to -1 to disable autoboot.
diff --git a/include/common.h b/include/common.h
index 4c3e3a6..acc4030 100644
--- a/include/common.h
+++ b/include/common.h
@@ -277,6 +277,14 @@ int	last_stage_init(void);
 extern ulong monitor_flash_len;
 int mac_read_from_eeprom(void);
 
+/*
+ * Called during a panic() when no console is available. The board should do
+ * its best to get a message to the user any way it can. This function should
+ * return if it can, in which case the system will either hang or reset.
+ * See panic().
+ */
+void board_panic_no_console(const char *str);
+
 /* common/flash.c */
 void flash_perror (int);
 
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 79dead3..56a2aef 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -24,6 +24,8 @@
 # define NUM_TYPE long long
 #define noinline __attribute__((noinline))
 
+DECLARE_GLOBAL_DATA_PTR;
+
 const char hex_asc[] = "0123456789abcdef";
 #define hex_asc_lo(x)   hex_asc[((x) & 0x0f)]
 #define hex_asc_hi(x)   hex_asc[((x) & 0xf0) >> 4]
@@ -714,12 +716,39 @@ int sprintf(char * buf, const char *fmt, ...)
 	return i;
 }
 
+#ifdef CONFIG_PRE_CONSOLE_PANIC
+/* Provide a default function for when no console is available */
+static void __board_panic_no_console(const char *msg)
+{
+	/* Just return since we can't access the console */
+}
+
+void board_panic_no_console(const char *msg) __attribute__((weak,
+					alias("__board_panic_no_console")));
+#endif
+
 void panic(const char *fmt, ...)
 {
 	va_list	args;
+
 	va_start(args, fmt);
+#ifdef CONFIG_PRE_CONSOLE_PANIC
+	{
+		char str[CONFIG_SYS_PBSIZE];
+
+		/* TODO)sjg): Move to vsnprintf() when available */
+		vsprintf(str, fmt, args);
+		if (gd->have_console) {
+			puts(str);
+			putc('\n');
+		} else {
+			board_panic_no_console(str);
+		}
+	}
+#else
 	vprintf(fmt, args);
 	putc('\n');
+#endif
 	va_end(args);
 #if defined (CONFIG_PANIC_HANG)
 	hang();
-- 
1.7.3.1