Re: [PATCH 2/5] drm/i915/dp: Add helper to get min sdp guardband

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

On 10/17/2025 4:20 PM, Hogander, Jouni wrote:
> On Fri, 2025-10-17 at 10:31 +0530, Ankit Nautiyal wrote:
>> Add a helper to compute vblank time needed for transmitting specific
>> DisplayPort SDPs like PPS, GAMUT_METADATA, and VSC_EXT. Latency is
>> based on line count per packet type.
>>
>> This will be used to ensure adequate guardband when features like
>> DSC/HDR
>> are enabled.
>>
>> Bspec: 70151
>> Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
>> ---
>>   drivers/gpu/drm/i915/display/intel_dp.c | 36
>> +++++++++++++++++++++++++
>>   drivers/gpu/drm/i915/display/intel_dp.h |  2 ++
>>   2 files changed, 38 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c
>> b/drivers/gpu/drm/i915/display/intel_dp.c
>> index 7059d55687cf..3f2c319e3d6f 100644
>> --- a/drivers/gpu/drm/i915/display/intel_dp.c
>> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
>> @@ -6990,3 +6990,39 @@ int intel_dp_compute_config_late(struct
>> intel_encoder *encoder,
>>   
>>   	return 0;
>>   }
>> +
>> +static
>> +int intel_dp_get_lines_for_sdp(u32 type)
>> +{
>> +	switch (type) {
>> +	case DP_SDP_VSC_EXT_VESA:
>> +	case DP_SDP_VSC_EXT_CEA:
>> +		return 10;
>> +	case HDMI_PACKET_TYPE_GAMUT_METADATA:
>> +		return 8;
>> +	case DP_SDP_PPS:
>> +		return 6;
> I found value 7 in the Bspec you are referring in commit message?

Hmm this indeed is 7, seems I misread the spec. Thanks for catching this!

Regards,

Ankit

>
> BR,
>
> Jouni Högander
>
>> +	default:
>> +		break;
>> +	}
>> +
>> +	return 0;
>> +}
>> +
>> +int intel_dp_sdp_min_guardband(const struct intel_crtc_state
>> *crtc_state,
>> +			       bool assume_all_enabled)
>> +{
>> +	int sdp_guardband = 0;
>> +
>> +	if (assume_all_enabled ||
>> +	    crtc_state->infoframes.enable &
>> +	
>> intel_hdmi_infoframe_enable(HDMI_PACKET_TYPE_GAMUT_METADATA))
>> +		sdp_guardband = max(sdp_guardband,
>> +				
>> intel_dp_get_lines_for_sdp(HDMI_PACKET_TYPE_GAMUT_METADATA));
>> +
>> +	if (assume_all_enabled ||
>> +	    crtc_state->dsc.compression_enable)
>> +		sdp_guardband = max(sdp_guardband,
>> intel_dp_get_lines_for_sdp(DP_SDP_PPS));
>> +
>> +	return sdp_guardband;
>> +}
>> diff --git a/drivers/gpu/drm/i915/display/intel_dp.h
>> b/drivers/gpu/drm/i915/display/intel_dp.h
>> index 281ced3a3b39..7ee5aeb28fe2 100644
>> --- a/drivers/gpu/drm/i915/display/intel_dp.h
>> +++ b/drivers/gpu/drm/i915/display/intel_dp.h
>> @@ -221,5 +221,7 @@ bool intel_dp_in_hdr_mode(const struct
>> drm_connector_state *conn_state);
>>   int intel_dp_compute_config_late(struct intel_encoder *encoder,
>>   				 struct intel_crtc_state
>> *crtc_state,
>>   				 struct drm_connector_state
>> *conn_state);
>> +int intel_dp_sdp_min_guardband(const struct intel_crtc_state
>> *crtc_state,
>> +			       bool assume_all_enabled);
>>   
>>   #endif /* __INTEL_DP_H__ */