[PATCH] init: Don't proxy the empty console= options to earlycon

[Raul E Rangel]

Right now we are proxying the `console=XXX` command line args to the
param_setup_earlycon. This is done because the early consoles used to
be enabled via the `console` parameter.

The `earlycon` parameter was added later by the commit 18a8bd949d6adb311
("serial: convert early_uart to earlycon for 8250"). It allowed to
setup the early consoles using another callback. And it was indeed
more self-explanatory and cleaner approach.

As a result, for example, the following parameters have the same effect:

    console=uart[8250],mmio,<addr>[,options]
    earlycon=uart[8250],mmio,<addr>[,options]

Nevertheless, `console` and `earlycon` parameters behave different when
the options do not match an early console. setup_earlycon() accepts only
console names in __earlycon_table. Also the empty options are handled
differently:

  + When `earlycon=` or just `earlycon` is specified on the command line,
    param_setup_earlycon() tries to enable an early console via the SPCR
    table or the device tree.

  + When `console=` is specified on the command line, it's intention is to
    disable the console.

Here comes the problem. The current code calls param_setup_earlycon()
even when `console=` is used with no options. As a result, it might
enable the early console when it is defined in the SPCR table or
a device tree. This is obviously not what users want.

The early console should be enabled via SPCR or DT only when `earlycon`
is used explicitly with no options.

Signed-off-by: Raul E Rangel <rrangel@xxxxxxxxxxxx>
[pmladek@xxxxxxxx: Add comments and more details into the commit message]
---
 init/main.c | 20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/init/main.c b/init/main.c
index ad920fac325c..3b059e316e62 100644
--- a/init/main.c
+++ b/init/main.c
@@ -733,13 +733,25 @@ static int __init do_early_param(char *param, char *val,
 	const struct obs_kernel_param *p;
 
 	for (p = __setup_start; p < __setup_end; p++) {
-		if ((p->early && parameq(param, p->str)) ||
-		    (strcmp(param, "console") == 0 &&
-		     strcmp(p->str, "earlycon") == 0)
-		) {
+		if (p->early && parameq(param, p->str)) {
 			if (p->setup_func(val) != 0)
 				pr_warn("Malformed early option '%s'\n", param);
 		}
+
+		/*
+		 * Early consoles can be historically enabled also when earlycon
+		 * specific options are passed via console=[earlycon options]
+		 * parameter.
+		 *
+		 * Do not try it with an empty value. "console=" is used to
+		 * disable real normal consoles. While "earlycon" is used to
+		 * enable an early console via SPCR or DT.
+		 */
+		if (strcmp(param, "console") == 0 && val && val[0] &&
+		    strcmp(p->str, "earlycon") == 0) {
+			if (p->setup_func(val) != 0)
+				pr_warn("Failed to setup earlycon via console=%s\n", val);
+		}
 	}
 	/* We accept everything at this stage. */
 	return 0;
-- 
2.35.3