[PATCH] drm/i915/display: fix display param dup for NULL char * params

[Jani Nikula <jani.nikula@intel.com>]

The display param duplication deviates from the original param
duplication in that it converts NULL params to to allocated empty
strings. This works for the vbt_firmware parameter, but not for
dmc_firmware_path, the user of which interprets NULL and the empty
string as distinct values. Specifically, the empty dmc_firmware_path
leads to DMC and PM being disabled.

Just remove the NULL check and pass it to kstrdup(), which safely
returns NULL for NULL input.

Fixes: 8015bee0bfec ("drm/i915/display: Add framework to add parameters specific to display")
Fixes: 0d82a0d6f556 ("drm/i915/display: move dmc_firmware_path to display params")
Cc: Jouni Högander <jouni.hogander@intel.com>
Cc: Luca Coelho <luciano.coelho@intel.com>
Cc: <stable@vger.kernel.org> # v6.8+
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
---
 drivers/gpu/drm/i915/display/intel_display_params.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_display_params.c b/drivers/gpu/drm/i915/display/intel_display_params.c
index c8e3d6892e23..49c6b42077dc 100644
--- a/drivers/gpu/drm/i915/display/intel_display_params.c
+++ b/drivers/gpu/drm/i915/display/intel_display_params.c
@@ -176,9 +176,9 @@ void intel_display_params_dump(struct drm_i915_private *i915, struct drm_printer
 #undef PRINT
 }
 
-__maybe_unused static void _param_dup_charp(char **valp)
+static void _param_dup_charp(char **valp)
 {
-	*valp = kstrdup(*valp ? *valp : "", GFP_ATOMIC);
+	*valp = kstrdup(*valp, GFP_ATOMIC);
 }
 
 __maybe_unused static void _param_nop(void *valp)
-- 
2.39.2