On Thu, 02 Feb 2023, "Kandpal, Suraj" <suraj.kandpal@xxxxxxxxx> wrote:
>>
>> On Thu, 02 Feb 2023, Suraj Kandpal <suraj.kandpal@xxxxxxxxx> wrote:
>> > According to Bpec: 49259 VDSC spec implies that 108 lines is an
>> > optimal slice height, but any size can be used as long as vertical
>> > active integer multiple and maximum vertical slice count requirements are
>> met.
>>
>> The commit message and subject should really indicate that this increases
>> the slice height considerably. It's a 13.5x increase at a minimum, could be
>> much more. Seems misleading to call it "fix logic", as if there's a small issue
>> somewhere.
>>
>> Bspec references should be here:
>>
>> Bspec: 49259
>> > Cc: Ankit Nautiyal <ankit.k.nautiyal@xxxxxxxxx>
>> > Cc: Swati Sharma <swati2.sharma@xxxxxxxxx>
>> > Signed-off-by: Suraj Kandpal <suraj.kandpal@xxxxxxxxx>
>> >
>> > diff --git a/drivers/gpu/drm/i915/display/intel_dp.c
>> > b/drivers/gpu/drm/i915/display/intel_dp.c
>> > index 62cbab7402e9..7bd2e56ef0fa 100644
>> > --- a/drivers/gpu/drm/i915/display/intel_dp.c
>> > +++ b/drivers/gpu/drm/i915/display/intel_dp.c
>> > @@ -1415,6 +1415,22 @@ static int
>> intel_dp_sink_dsc_version_minor(struct intel_dp *intel_dp)
>> > DP_DSC_MINOR_SHIFT;
>> > }
>> >
>> > +static int intel_dp_get_slice_height(int vactive)
>>
>> intel_dp_dsc_get_slice_height
>>
>> > +{
>> > + int slice_height;
>> > +
>> > + /*
>> > + * VDSC spec implies that 108 lines is an optimal slice height,
>>
>> Please be more specific with spec references than vague "VSDC spec". Spec
>> version is required at a minimum. Section and section title are a nice bonus.
>>
>> > + * but any size can be used as long as vertical active integer
>> > + * multiple and maximum vertical slice count requirements are met.
>> > + */
>> > + for (slice_height = 108; slice_height <= vactive; slice_height += 2)
>>
>> Where does it say 108 is a minimum, and you should go up only...?
>
> So in VDSC 1.2a section 3.8 option for slices it says
> "a slice height of 108 lines typically provides better
> performance than a slice height of 8 lines."
> It also states the following
> "Also it says There is no cost associated with slice height because
> there is no additional buffering or any other additional resources required"
> that's why I decided to move up from slice height of 108
>
>>
>> > + if (!(vactive % slice_height))
>>
>> Matter of taste, but please use (vactive % slice_height == 0) for clarity on
>> computations like this.
>>
>> > + return slice_height;
>> > +
>> > + return 0;
>>
>> I guess it's unlikely we ever hit here, but you could have the old code as
>> fallback and never return 0. Because you don't check for 0 in the caller
>> anyway.
>
> I will do this
>
>>
>> Also makes me wonder why we have intel_hdmi_dsc_get_slice_height()
>> separately, with almost identical implementation. Maybe we should
>> consolidate.
>
> That's separate because the minimum there starts from slice_height of 96 as indicated in
> HDMI spec
Do you think it's fine to duplicate a whole function if their sole
difference is the starting point of a for loop?
BR,
Jani.
>
> Regards,
> Suraj Kandpal
>>
>> > +}
>> > +
>> > static int intel_dp_dsc_compute_params(struct intel_encoder *encoder,
>> > struct intel_crtc_state *crtc_state) { @@
>> -1433,17
>> > +1449,7 @@ static int intel_dp_dsc_compute_params(struct intel_encoder
>> *encoder,
>> > vdsc_cfg->rc_model_size = DSC_RC_MODEL_SIZE_CONST;
>> > vdsc_cfg->pic_height = crtc_state->hw.adjusted_mode.crtc_vdisplay;
>> >
>> > - /*
>> > - * Slice Height of 8 works for all currently available panels. So start
>> > - * with that if pic_height is an integral multiple of 8. Eventually add
>> > - * logic to try multiple slice heights.
>> > - */
>> > - if (vdsc_cfg->pic_height % 8 == 0)
>> > - vdsc_cfg->slice_height = 8;
>> > - else if (vdsc_cfg->pic_height % 4 == 0)
>> > - vdsc_cfg->slice_height = 4;
>> > - else
>> > - vdsc_cfg->slice_height = 2;
>> > + vdsc_cfg->slice_height =
>> > +intel_dp_get_slice_height(vdsc_cfg->pic_height);
>> >
>> > ret = intel_dsc_compute_params(crtc_state);
>> > if (ret)
>>
>> --
>> Jani Nikula, Intel Open Source Graphics Center
--
Jani Nikula, Intel Open Source Graphics Center
