[PATCH v4 00/10] drm/msm: Fix math issues in MSM DSC implementation

[Marijn Suijten]

Various removals of complex yet unnecessary math, fixing all uses of
drm_dsc_config::bits_per_pixel to deal with the fact that this field
includes four fractional bits, and finally making sure that
range_bpg_offset contains values 6-bits wide to prevent overflows in
drm_dsc_pps_payload_pack().

Altogether this series is responsible for solving _all_ Display Stream
Compression issues and artifacts on the Sony Tama (sdm845) Akatsuki
smartphone (2880x1440p).

Changes since v3:
- Swap patch 7 and 8 to make sure msm_host is available inside
  dsi_populate_dsc_params();
- Reword patch 6 (Migrate to drm_dsc_compute_rc_parameters()) to more
  clearly explain why the FIXME wasn't solved initially, but why it can
  (and should!) be resolved now.

v3: https://lore.kernel.org/linux-arm-msm/20221009184824.457416-1-marijn.suijten@somainline.org/T/#u

Changes since v2:
- Generalize mux_word_size setting depending on bits_per_component;
- Migrate DSI's DSC calculations to drm_dsc_compute_rc_parameters(),
  implicitly addressing existing math issues;
- Disallow any bits_per_component other than 8, until hardcoded values
  are updated and tested to support such cases.

v2: https://lore.kernel.org/linux-arm-msm/20221005181657.784375-1-marijn.suijten@somainline.org/T/#u

Changes since v1:

- Propagate r-b's, except (obviously) in patches that were (heavily)
  modified;
- Remove accidental debug code in dsi_cmd_dma_add;
- Move Range BPG Offset masking out of DCS PPS packing, back into the
  DSI driver when it is assigned to drm_dsc_config (this series is now
  strictly focusing on drm/msm again);
- Replace modulo-check resulting in conditional increment with
  DIV_ROUND_UP;
- Remove repeated calculation of slice_chunk_size;
- Use u16 instead of int when handling bits_per_pixel;
- Use DRM_DEV_ERROR instead of pr_err in DSI code;
- Also remove redundant target_bpp_x16 variable.

v1: https://lore.kernel.org/linux-arm-msm/20221001190807.358691-1-marijn.suijten@somainline.org/T/#u

Marijn Suijten (10):
  drm/msm/dsi: Remove useless math in DSC calculations
  drm/msm/dsi: Remove repeated calculation of slice_per_intf
  drm/msm/dsi: Use DIV_ROUND_UP instead of conditional increment on
    modulo
  drm/msm/dsi: Reuse earlier computed dsc->slice_chunk_size
  drm/msm/dsi: Appropriately set dsc->mux_word_size based on bpc
  drm/msm/dsi: Migrate to drm_dsc_compute_rc_parameters()
  drm/msm/dsi: Account for DSC's bits_per_pixel having 4 fractional bits
  drm/msm/dsi: Disallow 8 BPC DSC configuration for alternative BPC
    values
  drm/msm/dpu1: Account for DSC's bits_per_pixel having 4 fractional
    bits
  drm/msm/dsi: Prevent signed BPG offsets from bleeding into adjacent
    bits

 drivers/gpu/drm/msm/disp/dpu1/dpu_hw_dsc.c |  11 +-
 drivers/gpu/drm/msm/dsi/dsi_host.c         | 121 ++++++---------------
 2 files changed, 37 insertions(+), 95 deletions(-)

--
2.38.1