Re: [PATCH 11/19] drm/i915/dp: Include all relevant AS SDP fields in comparison

["Nautiyal, Ankit K" <ankit.k.nautiyal@intel.com>]

On 3/30/2026 11:56 PM, Ville Syrjälä wrote:
> On Mon, Mar 30, 2026 at 09:36:48AM +0530, Ankit Nautiyal wrote:
>> Add missing drm_dp_as_sdp header fields to intel_compare_dp_as_sdp()
>> comparison.
>>
>> Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
>> ---
>>   drivers/gpu/drm/i915/display/intel_display.c | 5 ++++-
>>   1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
>> index 57870baebfa5..a0e7ef2574b2 100644
>> --- a/drivers/gpu/drm/i915/display/intel_display.c
>> +++ b/drivers/gpu/drm/i915/display/intel_display.c
>> @@ -4906,11 +4906,14 @@ static bool
>>   intel_compare_dp_as_sdp(const struct drm_dp_as_sdp *a,
>>   			const struct drm_dp_as_sdp *b)
>>   {
>> -	return a->revision == b->revision &&
>> +	return a->sdp_type == b->sdp_type &&
>> +		a->revision == b->revision &&
>> +		a->length == b->length &&
>>   		a->vtotal == b->vtotal &&
>>   		a->target_rr == b->target_rr &&
>>   		a->duration_incr_ms == b->duration_incr_ms &&
>>   		a->duration_decr_ms == b->duration_decr_ms &&
>> +		a->target_rr_divider == b->target_rr_divider &&
>>   		a->mode == b->mode;
> BTW do we know if the hardware actually modifies the AS SDP DIP buffer,
> or does it just override some of the values as the SDP is being
> transmitted? If the former then I guess we have to keep in mind that
> the readout may have to do some sanitizing to avoid mismatches,
> if we do anything that require the hardware to dynamically adjust
> the AS SDP.


There are some things HW sends on its own like bits 2 and 3 of DB0 :
  - Adaptive sync SDP transmission disable Bit 2 and
  - Remote frame buffer update Bit 3

I think it overrides those values instead of modifying the SDP DIP buffer.
That’s what the spec implies I suppose.

"When PR ALPM is Active (AS SDP Version 2), hardware will automatically 
drive DB0[3:2].
Software should always program these bits to zero."

Regards,
Ankit

>
> Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
>
>>   }
>>   
>> -- 
>> 2.45.2