Re: [PATCH v5 17/28] drm/i915/dsc: Compute Rate Control parameters for DSC

[Manasi Navare <manasi.d.navare@intel.com>]

On Mon, Oct 22, 2018 at 04:34:59PM -0700, Srivatsa, Anusha wrote:
> 
> ________________________________________
> From: Intel-gfx [intel-gfx-bounces@lists.freedesktop.org] on behalf of Manasi Navare [manasi.d.navare@intel.com]
> Sent: Friday, October 05, 2018 4:22 PM
> To: intel-gfx@lists.freedesktop.org; dri-devel@lists.freedesktop.org
> Subject: [Intel-gfx] [PATCH v5 17/28] drm/i915/dsc: Compute Rate Control parameters for DSC
> 
> From: Gaurav K Singh <gaurav.k.singh@intel.com>
> 
> This computation of RC params happens in the atomic commit phase
> during compute_config() to validate if display stream compression
> can be enabled for the requested mode.
> 
> v5 (From Manasi):
> * Fix dim checkpatch warnings/checks
> v4(From Gaurav):
> * No change.Rebase on drm-tip
> 
> v3 (From Gaurav):
> * Rebase on top of Manasi's latest series
> * Return -ve value in case of failure scenarios (Manasi)
> 
> Fix review comments from Ville:
> * Remove unnecessary comments
> * Remove unnecessary paranthesis
> * Add comments for few RC params calculations
> 
> v2 (From Manasi):
> * Rebase Gaurav's patch from intel-gfx to gfx-internal
> * Use struct drm_dsc_cfg instead of struct intel_dp
> as a parameter
> 
> Cc: Manasi Navare <manasi.d.navare@intel.com>
> Cc: Jani Nikula <jani.nikula@linux.intel.com>
> Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
> Signed-off-by: Gaurav K Singh <gaurav.k.singh@intel.com>
> Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
> ---
>  drivers/gpu/drm/i915/intel_vdsc.c | 127 ++++++++++++++++++++++++++++++
>  1 file changed, 127 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/intel_vdsc.c b/drivers/gpu/drm/i915/intel_vdsc.c
> index 351ea7d71c21..594196a9d0f4 100644
> --- a/drivers/gpu/drm/i915/intel_vdsc.c
> +++ b/drivers/gpu/drm/i915/intel_vdsc.c
> @@ -317,6 +317,130 @@ static int get_column_index_for_rc_params(u8 bits_per_component)
>         }
>  }
> 
> +static int intel_compute_rc_parameters(struct drm_dsc_config *vdsc_cfg)
> +{
> +       unsigned long groups_per_line = 0;
> +       unsigned long groups_total = 0;
> +       unsigned long num_extra_mux_bits = 0;
> +       unsigned long slice_bits = 0;
> +       unsigned long hrd_delay = 0;
> +       unsigned long final_scale = 0;
> +       unsigned long rbs_min = 0;
> +
> +       /* Number of groups used to code each line of a slice */
> +       groups_per_line = DIV_ROUND_UP(vdsc_cfg->slice_width,
> +                                      DSC_RC_PIXELS_PER_GROUP);
> +
> +       /* chunksize in Bytes */
> +       vdsc_cfg->slice_chunk_size = DIV_ROUND_UP(vdsc_cfg->slice_width *
> +                                                 vdsc_cfg->bits_per_pixel,
> +                                                 (8 * 16));
> +
> +       if (vdsc_cfg->convert_rgb)
> +               num_extra_mux_bits = 3 * (vdsc_cfg->mux_word_size +
> +                                         (4 * vdsc_cfg->bits_per_component + 4)
> +                                         - 2);
> +       else
> +               num_extra_mux_bits = 3 * vdsc_cfg->mux_word_size +
> +                       (4 * vdsc_cfg->bits_per_component + 4) +
> +                       2 * (4 * vdsc_cfg->bits_per_component) - 2;
> +       /* Number of bits in one Slice */
> +       slice_bits = 8 * vdsc_cfg->slice_chunk_size * vdsc_cfg->slice_height;
> +
> +       while ((num_extra_mux_bits > 0) &&
> +              ((slice_bits - num_extra_mux_bits) % vdsc_cfg->mux_word_size))
> +               num_extra_mux_bits--;
> +
> +       if (groups_per_line < vdsc_cfg->initial_scale_value - 8)
> +               vdsc_cfg->initial_scale_value = groups_per_line + 8;
> +
> +       /* scale_decrement_interval calculation according to DSC spec 1.11 */
> +       if (vdsc_cfg->initial_scale_value > 8)
> +               vdsc_cfg->scale_decrement_interval = groups_per_line /
> +                       (vdsc_cfg->initial_scale_value - 8);
> +       else
> +               vdsc_cfg->scale_decrement_interval = DSC_SCALE_DECREMENT_INTERVAL_MAX;
> +
> +       vdsc_cfg->final_offset = vdsc_cfg->rc_model_size -
> +               (vdsc_cfg->initial_xmit_delay *
> +                vdsc_cfg->bits_per_pixel + 8) / 16 + num_extra_mux_bits;
> +
> +       if (vdsc_cfg->final_offset >= vdsc_cfg->rc_model_size) {
> +               DRM_ERROR("FinalOfs < RcModelSze for this InitialXmitDelay\n");
> +               return -EINVAL;
> +       }
> +
> +       final_scale = (vdsc_cfg->rc_model_size * 8) /
> +               (vdsc_cfg->rc_model_size - vdsc_cfg->final_offset);
> +       if (vdsc_cfg->slice_height > 1)
> +               /*
> +                * NflBpgOffset is 16 bit value with 11 fractional bits
> +                * hence we multiply by 2^11 for preserving the
> +                * fractional part
> +                */
> +               vdsc_cfg->nfl_bpg_offset = DIV_ROUND_UP((vdsc_cfg->first_line_bpg_offset << 11),
> +                                                       (vdsc_cfg->slice_height - 1));
> +       else
> +               vdsc_cfg->nfl_bpg_offset = 0;
> +
> +       /* 2^16 - 1 */
> +       if (vdsc_cfg->nfl_bpg_offset > 65535) {
> +               DRM_ERROR("NflBpgOffset is too large for this slice height\n");
> +               return -EINVAL;
> +       }
> +
> +       /* Number of groups used to code the entire slice */
> +       groups_total = groups_per_line * vdsc_cfg->slice_height;
> +
> +       /* slice_bpg_offset is 16 bit value with 11 fractional bits */
> +       vdsc_cfg->slice_bpg_offset = DIV_ROUND_UP(((vdsc_cfg->rc_model_size -
> +                                                   vdsc_cfg->initial_offset +
> +                                                   num_extra_mux_bits) << 11),
> +                                                 groups_total);
> +
> +       if (final_scale > 0x9) {
> Why not just final_scale > 9?
>

We could use either, doesnt really matter in terms of compiler optimization. But from readibility
pov I can change it to use 9 instead.

With that change can I consider your r-b?

Manasi

> Anusha 
> +               /*
> +                * ScaleIncrementInterval =
> +                * finaloffset/((NflBpgOffset + SliceBpgOffset)*8(finalscale - 1.125))
> +                * as (NflBpgOffset + SliceBpgOffset) has 11 bit fractional value,
> +                * we need divide by 2^11 from pstDscCfg values
> +                */
> +               vdsc_cfg->scale_increment_interval =
> +                               (vdsc_cfg->final_offset * (1 << 11)) /
> +                               ((vdsc_cfg->nfl_bpg_offset +
> +                               vdsc_cfg->slice_bpg_offset)*
> +                               (final_scale - 9));
> +       } else {
> +               /*
> +                * If finalScaleValue is less than or equal to 9, a value of 0 should
> +                * be used to disable the scale increment at the end of the slice
> +                */
> +               vdsc_cfg->scale_increment_interval = 0;
> +       }
> +
> +       if (vdsc_cfg->scale_increment_interval > 65535) {
> +               DRM_ERROR("ScaleIncrementInterval is large for slice height\n");
> +               return -EINVAL;
> +       }
> +
> +       /*
> +        * DSC spec mentions that bits_per_pixel specifies the target
> +        * bits/pixel (bpp) rate that is used by the encoder,
> +        * in steps of 1/16 of a bit per pixel
> +        */
> +       rbs_min = vdsc_cfg->rc_model_size - vdsc_cfg->initial_offset +
> +               DIV_ROUND_UP(vdsc_cfg->initial_xmit_delay *
> +                            vdsc_cfg->bits_per_pixel, 16) +
> +               groups_per_line * vdsc_cfg->first_line_bpg_offset;
> +
> +       hrd_delay = DIV_ROUND_UP((rbs_min * 16), vdsc_cfg->bits_per_pixel);
> +       vdsc_cfg->rc_bits = (hrd_delay * vdsc_cfg->bits_per_pixel) / 16;
> +       vdsc_cfg->initial_dec_delay = hrd_delay - vdsc_cfg->initial_xmit_delay;
> +
> +       return 0;
> +}
> +
> +
>  int intel_dp_compute_dsc_params(struct intel_dp *intel_dp,
>                                 struct intel_crtc_state *pipe_config)
>  {
> @@ -451,5 +575,8 @@ int intel_dp_compute_dsc_params(struct intel_dp *intel_dp,
>         vdsc_cfg->initial_scale_value = (vdsc_cfg->rc_model_size << 3) /
>                 (vdsc_cfg->rc_model_size - vdsc_cfg->initial_offset);
> 
> +       if (intel_compute_rc_parameters(vdsc_cfg) < 0)
> +               return -1;
> +
>         return 0;
>  }
> --
> 2.18.0
> 
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