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

From: Abhinav Kumar
Date: Fri Oct 28 2022 - 14:33:45 EST


Hi Marijn

On 10/26/2022 11:28 AM, Marijn Suijten wrote:
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@xxxxxxxxxxxxxx/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@xxxxxxxxxxxxxx/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@xxxxxxxxxxxxxx/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


To keep the -fixes cycle to have only critical fixes (others are important too but are cleanups), I was thinking of absorbing patches 7,8,9 and 10 alone in the -fixes cycle and for patches 1-6, will go through the 6.2 push.

Let me know if there are any concerns if we just take patches 7,8,9 and 10 separately.

Thanks

Abhinav