RFC: bootm: Add silent_linux environment variable

At present the console for linux is silent if the U-Boot console is silent,
unless CONFIG_SILENT_U_BOOT_ONLY is set. I wonder if a better way would be
to have an environment variable to control this? Then we can control the
verbosity from scripts, and set the variable to 'no' for those boards that
want Linux to boot with console output.

Signed-off-by: Simon Glass <sjg@chromium.org>

README

@@ -4627,6 +4627,12 @@ List of environment variables (most likely not complete):
 
   npe_ucode	- set load address for the NPE microcode
 
+  silent_linux  - If set then linux will be told to boot silently, by
+		  changing the console to be empty. If "yes" it will be
+		  made silent. If "no" it will not be made silent. If
+		  unset, then it will be made silent if the U-Boot console
+		  is silent.
+
   tftpsrcport	- If this is set, the value is used for TFTP's
 		  UDP source port.
 

common/cmd_bootm.c

@@ -1384,9 +1384,19 @@ static void fixup_silent_linux(void)
 	char *buf;
 	const char *env_val;
 	char *cmdline = getenv("bootargs");
+	int want_silent;
 
-	/* Only fix cmdline when requested */
-	if (!(gd->flags & GD_FLG_SILENT))
+	/*
+	 * Only fix cmdline when requested. The environment variable can be:
+	 *
+	 *	no - we never fixup
+	 *	yes - we always fixup
+	 *	unset - we rely on the console silent flag
+	 */
+	want_silent = getenv_yesno("silent_linux");
+	if (want_silent == 0)
+		return;
+	else if (want_silent == -1 && !(gd->flags & GD_FLG_SILENT))
 		return;
 
 	debug("before silent fix-up: %s\n", cmdline);