earlycon: prevent multiple register_console()

If the earlycon parameter is given twice, the kernel will spit out a
WARN() in register_console() because it was already registered. The
non-dt variant setup_earlycon() already handles that gracefully. The dt
variant of_setup_earlycon() doesn't. Add the check there and add the
-EALREADY handling in early_init_dt_scan_chosen_stdout().

FWIW, this doesn't happen if CONFIG_ACPI_SPCR_TABLE is set. In that case
the registration is delayed until after earlycon parameter(s) are
parsed.

Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Michael Walle <michael@walle.cc>
Link: https://lore.kernel.org/r/20220628120705.200617-1-michael@walle.cc
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 3 insertions, 1 deletions

diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
index a8f5b6532165..043b12be22d6 100644
--- a/drivers/of/fdt.c
+++ b/drivers/of/fdt.c
@@ -1025,6 +1025,7 @@ int __init early_init_dt_scan_chosen_stdout(void)
 	int l;
 	const struct earlycon_id *match;
 	const void *fdt = initial_boot_params;
+	int ret;
 
 	offset = fdt_path_offset(fdt, "/chosen");
 	if (offset < 0)
@@ -1057,7 +1058,8 @@ int __init early_init_dt_scan_chosen_stdout(void)
 		if (fdt_node_check_compatible(fdt, offset, match->compatible))
 			continue;
 
-		if (of_setup_earlycon(match, offset, options) == 0)
+		ret = of_setup_earlycon(match, offset, options);
+		if (!ret || ret == -EALREADY)
 			return 0;
 	}
 	return -ENODEV;