Re: [Intel-gfx] [PATCH] drm/i915/bios: set default backlight controller index

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Tue, Feb 07, 2023 at 01:16:26PM +0200, Jani Nikula wrote:
> With backlight controller set to -1 in intel_panel_init_alloc() to
> distinguish uninitialized values, and controller later being set only if
> it's present in VBT, we can end up with -1 for the controller:
> 
>     [drm:intel_bios_init_panel [i915]] VBT backlight PWM modulation
>     frequency 200 Hz, active high, min brightness 0, level 255,
>     controller 4294967295
> 
> There's no harm if it happens on platforms that ignore controller due to
> only one backlight controller being present, like on VLV above, but play
> it safe.
> 
> Fixes: bf38bba3e7d6 ("drm/i915: Try to use the correct power sequencer intiially on bxt/glk")
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Signed-off-by: Jani Nikula <jani.nikula@intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_bios.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_bios.c b/drivers/gpu/drm/i915/display/intel_bios.c
> index e6ca51232dcf..ad833069f59c 100644
> --- a/drivers/gpu/drm/i915/display/intel_bios.c
> +++ b/drivers/gpu/drm/i915/display/intel_bios.c
> @@ -1033,6 +1033,7 @@ parse_lfp_backlight(struct drm_i915_private *i915,
>  	}
>  
>  	panel->vbt.backlight.type = INTEL_BACKLIGHT_DISPLAY_DDI;
> +	panel->vbt.backlight.controller = 0;
>  	if (i915->display.vbt.version >= 191) {
>  		size_t exp_size;

Ah right, older VBT didnt have this so we leave it untouched.
Zeroing in that case seems like the right thing to do.

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

-- 
Ville Syrjälä
Intel