Re: [Intel-gfx] [PATCH] drm/i915: Query compressed bpp properly using correct DPCD and DP Spec info

[Jani Nikula <jani.nikula@linux.intel.com>]

On Thu, 06 Apr 2023, "Lisovskiy, Stanislav" <stanislav.lisovskiy@intel.com> wrote:
> Not planning to upstream that actually, just for some bug on gitlab.
> Want to see if that helps the reporter, then at least there is an idea whats the problem.

The issue in drm_edp_dsc_sink_output_bpp() needs to be fixed regardless.

BR,
Jani.


>
> ________________________________________
> From: Jani Nikula <jani.nikula@linux.intel.com>
> Sent: Thursday, April 6, 2023 12:59 PM
> To: Lisovskiy, Stanislav; intel-gfx@lists.freedesktop.org
> Cc: Manasi Navare
> Subject: Re: [Intel-gfx] [PATCH] drm/i915: Query compressed bpp properly using correct DPCD and DP Spec info
>
> On Thu, 06 Apr 2023, Stanislav Lisovskiy <stanislav.lisovskiy@intel.com> wrote:
>> Currently we seem to be using wrong DPCD register for reading compressed bpps,
>> reading min/max input bpc instead of compressed bpp.
>> Fix that, so that we now apply min/max compressed bpp limitations we get
>> from DP Spec Table 2-157 DP v2.0 and/or correspondent DPCD register
>> DP_DSC_MAX_BITS_PER_PIXEL_LOW/HIGH.
>>
>> This might also allow us to get rid of an ugly compressed bpp recalculation,
>> which we had to add to make some MST hubs usable.
>>
>> Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
>> ---
>>  drivers/gpu/drm/i915/display/intel_dp_mst.c | 76 ++++++++++++++-------
>>  1 file changed, 52 insertions(+), 24 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c b/drivers/gpu/drm/i915/display/intel_dp_mst.c
>> index a88b852c437c..9479c7e0b269 100644
>> --- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
>> +++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
>> @@ -174,6 +174,50 @@ static int intel_dp_mst_compute_link_config(struct intel_encoder *encoder,
>>       return 0;
>>  }
>>
>> +static u16 dsc_max_sink_compressed_bppx16(const u8 dsc_dpcd[DP_DSC_RECEIVER_CAP_SIZE],
>> +                                       struct intel_crtc_state *pipe_config,
>> +                                       int bpc)
>> +{
>> +     u16 max_bppx16 = dsc_dpcd[DP_DSC_MAX_BITS_PER_PIXEL_LOW - DP_DSC_SUPPORT] |
>> +                      (dsc_dpcd[DP_DSC_MAX_BITS_PER_PIXEL_HI - DP_DSC_SUPPORT] &
>> +                       DP_DSC_MAX_BITS_PER_PIXEL_HI_MASK << DP_DSC_MAX_BITS_PER_PIXEL_HI_SHIFT);
>
> This duplicates drm_edp_dsc_sink_output_bpp().
>
> Both have operator precedence wrong, leading to the high byte always
> being ignored. For example, sink reported max bpp of 32 turns to 0, and
> 24 turns to 8.
>
> Broken since 2018. 0575650077ea ("drm/dp: DRM DP helper/macros to get DP
> sink DSC parameters").
>
> The definition of DP_DSC_MAX_BITS_PER_PIXEL_HI_SHIFT is misleading wrt
> all of our regular usage. We should never have a FOO_MASK << FOO_SHIFT
> in code, the MASK should always be already shifted in place. Here we do,
> because the shift is not for shifting the mask in place, it's for
> combining the high and low bytes. But I don't really think
> DP_DSC_MAX_BITS_PER_PIXEL_HI_SHIFT should exist, at all.
>
> BR,
> Jani.
>
>
>
>> +
>> +     if (max_bppx16)
>> +             return max_bppx16;
>> +     /*
>> +      * If support not given in DPCD 67h, 68h use the Maximum Allowed bit rate
>> +      * values as given in spec Table 2-157 DP v2.0
>> +      */
>> +     switch (pipe_config->output_format) {
>> +     case INTEL_OUTPUT_FORMAT_RGB:
>> +     case INTEL_OUTPUT_FORMAT_YCBCR444:
>> +             return bpc << 4;
>> +     case INTEL_OUTPUT_FORMAT_YCBCR420:
>> +             return (3 * (bpc / 2)) << 4;
>> +     default:
>> +             MISSING_CASE(pipe_config->output_format);
>> +             break;
>> +     }
>> +
>> +     return 0;
>> +}
>> +
>> +static u16 dsc_min_compressed_bppx16(struct intel_crtc_state *pipe_config)
>> +{
>> +     switch (pipe_config->output_format) {
>> +     case INTEL_OUTPUT_FORMAT_RGB:
>> +     case INTEL_OUTPUT_FORMAT_YCBCR444:
>> +             return 8 << 4;
>> +     case INTEL_OUTPUT_FORMAT_YCBCR420:
>> +             return 6 << 4;
>> +     default:
>> +             MISSING_CASE(pipe_config->output_format);
>> +             break;
>> +     }
>> +
>> +     return 0;
>> +}
>> +
>>  static int intel_dp_dsc_mst_compute_link_config(struct intel_encoder *encoder,
>>                                               struct intel_crtc_state *crtc_state,
>>                                               struct drm_connector_state *conn_state,
>> @@ -191,8 +235,6 @@ static int intel_dp_dsc_mst_compute_link_config(struct intel_encoder *encoder,
>>       u8 dsc_bpc[3] = {0};
>>       int min_bpp, max_bpp, sink_min_bpp, sink_max_bpp;
>>       u8 dsc_max_bpc;
>> -     bool need_timeslot_recalc = false;
>> -     u32 last_compressed_bpp;
>>
>>       /* Max DSC Input BPC for ICL is 10 and for TGL+ is 12 */
>>       if (DISPLAY_VER(i915) >= 12)
>> @@ -228,6 +270,14 @@ static int intel_dp_dsc_mst_compute_link_config(struct intel_encoder *encoder,
>>       if (max_bpp > sink_max_bpp)
>>               max_bpp = sink_max_bpp;
>>
>> +     /* Get Min/Max compressed bpp's for those Input Bpps we got for source/sink */
>> +     max_bpp = min(max_bpp, dsc_max_sink_compressed_bppx16(intel_dp->dsc_dpcd, crtc_state, max_bpp / 3) >> 4);
>> +     min_bpp = max(min_bpp, dsc_min_compressed_bppx16(crtc_state) >> 4);
>> +
>> +     /* Align compressed bpps according to our own constraints */
>> +     max_bpp = intel_dp_dsc_nearest_valid_bpp(i915, max_bpp, crtc_state->pipe_bpp);
>> +     min_bpp = intel_dp_dsc_nearest_valid_bpp(i915, min_bpp, crtc_state->pipe_bpp);
>> +
>>       slots = intel_dp_mst_find_vcpi_slots_for_bpp(encoder, crtc_state, max_bpp,
>>                                                    min_bpp, limits,
>>                                                    conn_state, 2 * 3, true);
>> @@ -235,28 +285,6 @@ static int intel_dp_dsc_mst_compute_link_config(struct intel_encoder *encoder,
>>       if (slots < 0)
>>               return slots;
>>
>> -     last_compressed_bpp = crtc_state->dsc.compressed_bpp;
>> -
>> -     crtc_state->dsc.compressed_bpp = intel_dp_dsc_nearest_valid_bpp(i915,
>> -                                                                     last_compressed_bpp,
>> -                                                                     crtc_state->pipe_bpp);
>> -
>> -     if (crtc_state->dsc.compressed_bpp != last_compressed_bpp)
>> -             need_timeslot_recalc = true;
>> -
>> -     /*
>> -      * Apparently some MST hubs dislike if vcpi slots are not matching precisely
>> -      * the actual compressed bpp we use.
>> -      */
>> -     if (need_timeslot_recalc) {
>> -             slots = intel_dp_mst_find_vcpi_slots_for_bpp(encoder, crtc_state,
>> -                                                          crtc_state->dsc.compressed_bpp,
>> -                                                          crtc_state->dsc.compressed_bpp,
>> -                                                          limits, conn_state, 2 * 3, true);
>> -             if (slots < 0)
>> -                     return slots;
>> -     }
>> -
>>       intel_link_compute_m_n(crtc_state->dsc.compressed_bpp,
>>                              crtc_state->lane_count,
>>                              adjusted_mode->crtc_clock,
>
> --
> Jani Nikula, Intel Open Source Graphics Center

-- 
Jani Nikula, Intel Open Source Graphics Center