Re: [PATCH] drm/i915: optimzie eDP 1.4 config

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

On Tue, 04 Sep 2018, Chris Wilson <chris@chris-wilson.co.uk> wrote:
> Quoting Lee, Shawn C (2018-09-04 15:55:41)
>> eDP 1.4 introduce a new link rates flexibility and selection.
>> It provided system specific link rate optimization and power
>> efficiency. We should keep eDP 1.3 and older version to use
>> max link rate approach to avoid any side effect. And eDP 1.4
>> used the optimization link rate and lane count setting.
>> 
>> Cc: Matt Atwood <matthew.s.atwood@intel.com>
>> Signed-off-by: Lee, Shawn C <shawn.c.lee@intel.com>
>> ---
>>  drivers/gpu/drm/i915/intel_dp.c | 6 ++++--
>>  1 file changed, 4 insertions(+), 2 deletions(-)
>> 
>> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
>> index 436c22de33b6..903d640fe712 100644
>> --- a/drivers/gpu/drm/i915/intel_dp.c
>> +++ b/drivers/gpu/drm/i915/intel_dp.c
>> @@ -1953,8 +1953,10 @@ intel_dp_compute_link_config(struct intel_encoder *encoder,
>>                  * configuration, and typically these values correspond to the
>>                  * native resolution of the panel.
>>                  */
>
> Having just finished a comment explaining why we override the limits for
> eDP, the following logic is confusing without at least a mention above.

I think the proper approach with the appropriate explanations is [1]. I
think it's harmful to start optimizing on eDP 1.4 without also
optimizing for fast and narrow link per spec at the same time.

BR,
Jani.


[1] http://patchwork.freedesktop.org/patch/msgid/20180905095321.13843-1-jani.nikula@intel.com



>
>> -               limits.min_lane_count = limits.max_lane_count;
>> -               limits.min_clock = limits.max_clock;
>> +               if (intel_dp->edp_dpcd[0] <= DP_EDP_13) {
>> +                       limits.min_lane_count = limits.max_lane_count;
>> +                       limits.min_clock = limits.max_clock;
>> +               }
>>         }
>>  
>>         intel_dp_adjust_compliance_config(intel_dp, pipe_config, &limits);
>> -- 
>> 2.7.4
>> 
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-- 
Jani Nikula, Intel Open Source Graphics Center
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