On Mon, Sep 22, 2025 at 10:35:42PM +0300, Ville Syrjälä wrote:
> On Fri, Sep 19, 2025 at 12:12:22AM +0300, Imre Deak wrote:
> > Read out the branch devices' maximum overall DSC pixel throughput and
> > line width and verify the mode's corresponding pixel clock and hactive
> > period against these.
> >
> > Signed-off-by: Imre Deak <imre.d...@intel.com>
> > ---
> > .../drm/i915/display/intel_display_types.h | 8 +++
> > drivers/gpu/drm/i915/display/intel_dp.c | 62 +++++++++++++++++++
> > 2 files changed, 70 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/i915/display/intel_display_types.h
> > b/drivers/gpu/drm/i915/display/intel_display_types.h
> > index 358ab922d7a76..73bdafae604f8 100644
> > --- a/drivers/gpu/drm/i915/display/intel_display_types.h
> > +++ b/drivers/gpu/drm/i915/display/intel_display_types.h
> > @@ -552,6 +552,14 @@ struct intel_connector {
> >
> > u8 dsc_hblank_expansion_quirk:1;
> > u8 dsc_decompression_enabled:1;
> > +
> > + struct {
> > + struct {
> > + int rgb_yuv444;
> > + int yuv422_420;
> > + } overall_throughput;
> > + int max_line_width;
> > + } dsc_branch_caps;
> > } dp;
> >
> > struct {
> > diff --git a/drivers/gpu/drm/i915/display/intel_dp.c
> > b/drivers/gpu/drm/i915/display/intel_dp.c
> > index 8cc123b0fd752..dd082d2fcc968 100644
> > --- a/drivers/gpu/drm/i915/display/intel_dp.c
> > +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> > @@ -1042,6 +1042,20 @@ u8 intel_dp_dsc_get_slice_count(const struct
> > intel_connector *connector,
> > int tp_yuv422_420;
> > u8 val;
> >
> > + /*
> > + * TODO: Use the throughput value specific to the actual RGB/YUV
> > + * format of the output.
> > + * 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.
> > + */
> > + if (mode_clock >
> > max(connector->dp.dsc_branch_caps.overall_throughput.rgb_yuv444,
> > +
> > connector->dp.dsc_branch_caps.overall_throughput.yuv422_420))
> > + return 0;
> > +
> > + if (mode_hdisplay > connector->dp.dsc_branch_caps.max_line_width)
> > + return 0;
>
> Looks like you only initialize these when the branch device supports
> decompression. What about a branch device that can do pass-through but
> no decompression? Should we even be checking these when doing
> pass-through?
Ah, we read them from the decompression_aux, which I presume is always
the thing that we want to do the decompression.
So in the passthrough case it will be the sink, and then we take the
early !is_branch exit from init_dsc_overall_throughput_limits().
Same for eDP.
>
> > +
> > 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,
> > @@ -4204,6 +4218,44 @@ static void intel_dp_read_dsc_dpcd(struct drm_dp_aux
> > *aux,
> > dsc_dpcd);
> > }
> >
> > +static int dsc_branch_overall_throughput(u8 bw_code)
> > +{
> > + switch (bw_code) {
> > + case 0:
> > + return INT_MAX;
> > + case 1:
> > + return 680000;
> > + default:
> > + return 600000 + 50000 * bw_code;
> > + }
> > +}
> > +
> > +static void init_dsc_overall_throughput_limits(struct intel_connector
> > *connector, bool is_branch)
> > +{
> > + u8 branch_caps[3];
> > +
> > + connector->dp.dsc_branch_caps.overall_throughput.rgb_yuv444 = INT_MAX;
> > + connector->dp.dsc_branch_caps.overall_throughput.yuv422_420 = INT_MAX;
> > + connector->dp.dsc_branch_caps.max_line_width = INT_MAX;
> > +
> > + if (!is_branch)
> > + return;
> > +
> > + if (drm_dp_dpcd_read_data(connector->dp.dsc_decompression_aux,
> > + DP_DSC_BRANCH_OVERALL_THROUGHPUT_0,
> > branch_caps,
> > + sizeof(branch_caps)) != 0)
> > + return;
> > +
> > + connector->dp.dsc_branch_caps.overall_throughput.rgb_yuv444 =
> > + dsc_branch_overall_throughput(branch_caps[0]);
> > +
> > + connector->dp.dsc_branch_caps.overall_throughput.yuv422_420 =
> > + dsc_branch_overall_throughput(branch_caps[1]);
> > +
> > + if (branch_caps[2] != 0)
> > + connector->dp.dsc_branch_caps.max_line_width = branch_caps[2] *
> > 320;
>
> That max line width calculation should probably be a function as well
> so that it can later be moved into some drm helper file along with the
> other functions.
>
> > +}
> > +
> > void intel_dp_get_dsc_sink_cap(u8 dpcd_rev,
> > const struct drm_dp_desc *desc, bool is_branch,
> > struct intel_connector *connector)
> > @@ -4219,6 +4271,8 @@ void intel_dp_get_dsc_sink_cap(u8 dpcd_rev,
> > /* Clear fec_capable to avoid using stale values */
> > connector->dp.fec_capability = 0;
> >
> > + memset(&connector->dp.dsc_branch_caps, 0,
> > sizeof(connector->dp.dsc_branch_caps));
> > +
> > if (dpcd_rev < DP_DPCD_REV_14)
> > return;
> >
> > @@ -4233,6 +4287,11 @@ void intel_dp_get_dsc_sink_cap(u8 dpcd_rev,
> >
> > drm_dbg_kms(display->drm, "FEC CAPABILITY: %x\n",
> > connector->dp.fec_capability);
> > +
> > + if (!(connector->dp.dsc_dpcd[0] & DP_DSC_DECOMPRESSION_IS_SUPPORTED))
> > + return;
> > +
> > + init_dsc_overall_throughput_limits(connector, is_branch);
> > }
> >
> > static void intel_edp_get_dsc_sink_cap(u8 edp_dpcd_rev, struct
> > intel_connector *connector)
> > @@ -4241,6 +4300,9 @@ static void intel_edp_get_dsc_sink_cap(u8
> > edp_dpcd_rev, struct intel_connector *
> > return;
> >
> > intel_dp_read_dsc_dpcd(connector->dp.dsc_decompression_aux,
> > connector->dp.dsc_dpcd);
> > +
> > + if (connector->dp.dsc_dpcd[0] & DP_DSC_DECOMPRESSION_IS_SUPPORTED)
> > + init_dsc_overall_throughput_limits(connector, false);
> > }
> >
> > static void
> > --
> > 2.49.1
>
> --
> Ville Syrjälä
> Intel
--
Ville Syrjälä
Intel
