On Mon, Sep 22, 2025 at 10:34:40PM +0300, Ville Syrjälä wrote:
> On Fri, Sep 19, 2025 at 12:12:20AM +0300, Imre Deak wrote:
> > Use the branch device's actual per-slice peak throughput to calculate
> > the minimum number of required DSC slices, falling back to the
> > hard-coded throughput values (as suggested by the DP Standard) if the
> > device's reported throughput value is 0.
> >
> > For now use the minimum of the two throughput values, which is ok,
> > potentially resulting in a higher than required minimum slice count.
> > This doesn't change the current way of using the same minimum throughput
> > value regardless of the RGB/YUV output format used.
> >
> > Signed-off-by: Imre Deak <[email protected]>
> > ---
> > drivers/gpu/drm/i915/display/intel_dp.c | 47 +++++++++++++++++++++----
> > 1 file changed, 41 insertions(+), 6 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/display/intel_dp.c
> > b/drivers/gpu/drm/i915/display/intel_dp.c
> > index 2eab591a8ef56..a963a58c87372 100644
> > --- a/drivers/gpu/drm/i915/display/intel_dp.c
> > +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> > @@ -1011,6 +1011,26 @@ u16 intel_dp_dsc_get_max_compressed_bpp(struct
> > intel_display *display,
> > return bits_per_pixel;
> > }
> >
> > +static int dsc_per_slice_throughput(struct intel_display *display, int
> > mode_clock, int bw_code)
>
> s/bw_code/throughput_mode/ or something maybe to make it match the spec
> a bit better? "bw_code" is I think what we've been calling the
> LINK_BW_SET value.
Ok, will use throughput.
>
> > +{
> > + switch (bw_code) {
> > + case 0:
> > + if (mode_clock <= DP_DSC_PEAK_PIXEL_RATE)
> > + return DP_DSC_MAX_ENC_THROUGHPUT_0;
> > + else
> > + return DP_DSC_MAX_ENC_THROUGHPUT_1;
>
> These look like some unhelpful single use defines. I'd get
> rid of them and just stick the actual numbers here.
Ok, agreed, will remove/inline the defines. The Standard actually
describes a 3rd range as well above 4800 MPixel/s, will add that too.
> > + case 1:
> > + return 340000;
> > + case 2 ... 14:
> > + return 400000 + 50000 * (bw_code - 2);
> > + case 15:
> > + return 170000;
> > + default:
> > + drm_err(display->drm, "Invalid DSC peak throughput code\n");
>
> This whole thing looks like it belongs in some drm helper.
> Probably best to pass in struct drm_device from the start
> so that moving it over will later be easier.
Ok, agreed. Moved this now and the other DSC branch query functions in
this patchset to drm_dp_helper.c as in patch [1] in branch [2].
[1] https://github.com/ideak/linux/commit/7f7cab2746f4
[2] https://github.com/ideak/linux/commits/dsc-bpp-quirk
>
> > + return 340000;
> > + }
> > +}
> > +
> > u8 intel_dp_dsc_get_slice_count(const struct intel_connector *connector,
> > int mode_clock, int mode_hdisplay,
> > int num_joined_pipes)
> > @@ -1018,13 +1038,28 @@ u8 intel_dp_dsc_get_slice_count(const struct
> > intel_connector *connector,
> > struct intel_display *display = to_intel_display(connector);
> > u8 min_slice_count, i;
> > int max_slice_width;
> > + int tp_rgb_yuv444;
> > + int tp_yuv422_420;
> > + u8 val;
> >
> > - if (mode_clock <= DP_DSC_PEAK_PIXEL_RATE)
> > - min_slice_count = DIV_ROUND_UP(mode_clock,
> > - DP_DSC_MAX_ENC_THROUGHPUT_0);
> > - else
> > - min_slice_count = DIV_ROUND_UP(mode_clock,
> > - DP_DSC_MAX_ENC_THROUGHPUT_1);
> > + val = connector->dp.dsc_dpcd[DP_DSC_PEAK_THROUGHPUT - DP_DSC_SUPPORT];
> > + tp_rgb_yuv444 = dsc_per_slice_throughput(display, mode_clock,
> > +
> > REG_FIELD_GET8(DP_DSC_THROUGHPUT_MODE_0_MASK,
> > + val));
> > + tp_yuv422_420 = dsc_per_slice_throughput(display, mode_clock,
> > +
> > REG_FIELD_GET8(DP_DSC_THROUGHPUT_MODE_1_MASK,
> > + val));
> > +
> > + /*
> > + * TODO: Use the throughput value specific to the actual RGB/YUV
> > + * format of the output.
> > + * For now use the smaller of these, which is ok, potentially
> > + * resulting in a higher than required minimum slice count.
> > + * The RGB/YUV444 throughput value should be always either equal
> > + * or smaller than the YUV422/420 value, but let's not depend on
> > + * this assumption.
> > + */
> > + min_slice_count = DIV_ROUND_UP(mode_clock, min(tp_rgb_yuv444,
> > tp_yuv422_420));
> >
> > /*
> > * Due to some DSC engine BW limitations, we need to enable second
> > --
> > 2.49.1
>
> --
> Ville Syrjälä
> Intel
