[PATCH] drm/i915/dp: Update dfp caps only if its a branch device

[Nautiyal, Ankit K]

On 12/11/2023 2:24 PM, Jani Nikula wrote:
> On Mon, 11 Dec 2023, Ankit Nautiyal <ankit.k.nautiyal at intel.com> wrote:
>> Avoid checking for Downstream Facing Port capabilities,
>> if its not a DP branch device.
> Why?
>
> The commit message *always* needs to answer the question why. This
> commit message describes what the patch does in English.

Hi Jani,

This was in response to a failure seen sometimes with some DP/eDP panels 
while reading DPCDs  meant for PCON capabilities.

Perhaps, I Should have started with this, instead of being lazy, 
apologies for that.

Since downward facing port capabilities are for DP branch device, I 
wondered if some panels would have problems if we read this.

However, I am realizing, that the DPCD read should still work and 
perhaps read 0x0 even if the device do not have the capabilities.


Regards,

Ankit


>
>
> BR,
> Jani.
>
>> Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal at intel.com>
>> ---
>>   drivers/gpu/drm/i915/display/intel_dp.c | 3 +++
>>   1 file changed, 3 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
>> index 3b2482bf683f..bef797b63000 100644
>> --- a/drivers/gpu/drm/i915/display/intel_dp.c
>> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
>> @@ -5502,6 +5502,9 @@ intel_dp_update_dfp(struct intel_dp *intel_dp,
>>   	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
>>   	struct intel_connector *connector = intel_dp->attached_connector;
>>   
>> +	if (!drm_dp_is_branch(intel_dp->dpcd))
>> +		return;
>> +
>>   	intel_dp->dfp.max_bpc =
>>   		drm_dp_downstream_max_bpc(intel_dp->dpcd,
>>   					  intel_dp->downstream_ports, drm_edid);