[Intel-gfx] [PATCH v3 2/6] drm/i915: Remove the link rate and lane count loop in compute config

[Jani Nikula]

On Mon, 26 Sep 2016, Jani Nikula <jani.nikula at linux.intel.com> wrote:
> On Fri, 16 Sep 2016, Manasi Navare <manasi.d.navare at intel.com> wrote:
>> While configuring the pipe during modeset, it should use
>> max clock and max lane count and reduce the bpp until
>> the requested mode rate is less than or equal to
>> available link BW.
>> This is required to pass DP Compliance.
>
> As I wrote in reply to patch 1/6, this is not a DP spec requirement. The
> link policy maker can freely choose the link parameters as long as the
> sink supports them.

Also double checked the DP link CTS spec. AFAICT none of the tests
expect the source to use the max clock or max lane count
directly. (Automated test request is another matter, and we should look
at it.)

I think patches 1-2 are based on an incorrect interpretation of the spec
and tests.

BR,
Jani.


>
> BR,
> Jani.
>
>
>>
>> v3:
>> * Add Debug print if requested mode cannot be supported
>> during modeset (Dhinakaran Pandiyan)
>> v2:
>> * Removed the loop since we use max values of clock
>> and lane count (Dhinakaran Pandiyan)
>>
>> Signed-off-by: Manasi Navare <manasi.d.navare at intel.com>
>> ---
>>  drivers/gpu/drm/i915/intel_dp.c | 22 ++++++++--------------
>>  1 file changed, 8 insertions(+), 14 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
>> index d81c67cb..65b4559 100644
>> --- a/drivers/gpu/drm/i915/intel_dp.c
>> +++ b/drivers/gpu/drm/i915/intel_dp.c
>> @@ -1644,23 +1644,17 @@ intel_dp_compute_config(struct intel_encoder *encoder,
>>  	for (; bpp >= 6*3; bpp -= 2*3) {
>>  		mode_rate = intel_dp_link_required(adjusted_mode->crtc_clock,
>>  						   bpp);
>> +		clock = max_clock;
>> +		lane_count = max_lane_count;
>> +		link_clock = common_rates[clock];
>> +		link_avail = intel_dp_max_data_rate(link_clock,
>> +						    lane_count);
>>  
>> -		for (clock = min_clock; clock <= max_clock; clock++) {
>> -			for (lane_count = min_lane_count;
>> -				lane_count <= max_lane_count;
>> -				lane_count <<= 1) {
>> -
>> -				link_clock = common_rates[clock];
>> -				link_avail = intel_dp_max_data_rate(link_clock,
>> -								    lane_count);
>> -
>> -				if (mode_rate <= link_avail) {
>> -					goto found;
>> -				}
>> -			}
>> -		}
>> +		if (mode_rate <= link_avail)
>> +			goto found;
>>  	}
>>  
>> +	DRM_DEBUG_KMS("Requested Mode Rate not supported\n");
>>  	return false;
>>  
>>  found:

-- 
Jani Nikula, Intel Open Source Technology Center