Re: [PATCH 1/5] drm/i915/dp: Fix readback for target_rr in Adaptive Sync SDP

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

On 10/30/2025 1:48 PM, Ville Syrjälä wrote:
> On Thu, Oct 30, 2025 at 10:47:51AM +0530, Ankit Nautiyal wrote:
>> Correct the bit-shift logic to properly readback the 10 bit target_rr from
>> DB3 and DB4.
>>
>> Fixes: 12ea89291603 ("drm/i915/dp: Add Read/Write support for Adaptive Sync SDP")
>> Cc: Mitul Golani <mitulkumar.ajitkumar.golani@intel.com>
>> Cc: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
>> Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
>> ---
>>   drivers/gpu/drm/i915/display/intel_dp.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
>> index 475518b4048b..c013eb2e18a1 100644
>> --- a/drivers/gpu/drm/i915/display/intel_dp.c
>> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
>> @@ -4996,7 +4996,7 @@ int intel_dp_as_sdp_unpack(struct drm_dp_as_sdp *as_sdp,
>>   	as_sdp->length = sdp->sdp_header.HB3 & DP_ADAPTIVE_SYNC_SDP_LENGTH;
>>   	as_sdp->mode = sdp->db[0] & DP_ADAPTIVE_SYNC_SDP_OPERATION_MODE;
>>   	as_sdp->vtotal = (sdp->db[2] << 8) | sdp->db[1];
>> -	as_sdp->target_rr = (u64)sdp->db[3] | ((u64)sdp->db[4] & 0x3);
>> +	as_sdp->target_rr = (u64)sdp->db[3] | ((u64)(sdp->db[4] & 0x3) << 8);
> The (u64) casts are completely pointless. And I would try to write this
> in a styple that is more consistent with the vtotal assignment right
> above it. Eg.: target_rr = ((db[4] & 0x3) << 8) | db[3];


Makes sense. Will change this as suggested.


Regards,

Ankit

>
>>   	as_sdp->target_rr_divider = sdp->db[4] & 0x20 ? true : false;
>>   
>>   	return 0;
>> -- 
>> 2.45.2