Re: [PATCH] drm/i915/dp: fall back to 18 bpp when sink capability is unknown

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

On Wed, 13 Jan 2016, Ville Syrjälä <ville.syrjala@linux.intel.com> wrote:
> On Wed, Jan 13, 2016 at 04:35:20PM +0200, Jani Nikula wrote:
>> Per DP spec, the source device should fall back to 18 bpp, VESA range
>> RGB when the sink capability is unknown. Fix the color depth
>> clamping. 18 bpp color depth should ensure full color range in automatic
>> mode.
>> 
>> The clamping has been HDMI specific since its introduction in
>> 
>> commit 996a2239f93b03c5972923f04b097f65565c5bed
>> Author: Daniel Vetter <daniel.vetter@ffwll.ch>
>> Date:   Fri Apr 19 11:24:34 2013 +0200
>> 
>>     drm/i915: Disable high-bpc on pre-1.4 EDID screens
>> 
>> Cc: stable@vger.kernel.org
>> Reported-by: Dihan Wickremasuriya <nayomal@gmail.com>
>> Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=105331
>> Signed-off-by: Jani Nikula <jani.nikula@intel.com>
>
> Makes sense to me as far as the spec is concerned.
> Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

Also got Tested-by in the bug. Pushed to drm-intel-next-queued, thanks
for the review.

BR,
Jani.


>
>> ---
>>  drivers/gpu/drm/i915/intel_display.c | 20 +++++++++++++++-----
>>  1 file changed, 15 insertions(+), 5 deletions(-)
>> 
>> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
>> index 07ca19b0ec17..6eaecd9385ab 100644
>> --- a/drivers/gpu/drm/i915/intel_display.c
>> +++ b/drivers/gpu/drm/i915/intel_display.c
>> @@ -12171,11 +12171,21 @@ connected_sink_compute_bpp(struct intel_connector *connector,
>>  		pipe_config->pipe_bpp = connector->base.display_info.bpc*3;
>>  	}
>>  
>> -	/* Clamp bpp to 8 on screens without EDID 1.4 */
>> -	if (connector->base.display_info.bpc == 0 && bpp > 24) {
>> -		DRM_DEBUG_KMS("clamping display bpp (was %d) to default limit of 24\n",
>> -			      bpp);
>> -		pipe_config->pipe_bpp = 24;
>> +	/* Clamp bpp to default limit on screens without EDID 1.4 */
>> +	if (connector->base.display_info.bpc == 0) {
>> +		int type = connector->base.connector_type;
>> +		int clamp_bpp = 24;
>> +
>> +		/* Fall back to 18 bpp when DP sink capability is unknown. */
>> +		if (type == DRM_MODE_CONNECTOR_DisplayPort ||
>> +		    type == DRM_MODE_CONNECTOR_eDP)
>> +			clamp_bpp = 18;
>> +
>> +		if (bpp > clamp_bpp) {
>> +			DRM_DEBUG_KMS("clamping display bpp (was %d) to default limit of %d\n",
>> +				      bpp, clamp_bpp);
>> +			pipe_config->pipe_bpp = clamp_bpp;
>> +		}
>>  	}
>>  }
>>  
>> -- 
>> 2.1.4

-- 
Jani Nikula, Intel Open Source Technology Center
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