[PATCH RFC v2 0/7] drm/display: dp: add new DPCD access functions

[Dmitry Baryshkov]

Existing DPCD access functions return an error code or the number of
bytes being read / write in case of partial access. However a lot of
drivers either (incorrectly) ignore partial access or mishandle error
codes. In other cases this results in a boilerplate code which compares
returned value with the size.

As suggested by Jani implement new set of DPCD access helpers, which
ignore partial access, always return 0 or an error code. Reimplement
existing helpers using the new functions to ensure backwards
compatibility.

This series targets only the DRM helpers code. If the approach is found
to be acceptable, each of the drivers should be converted on its own.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov at linaro.org>
---
Changes in v2:
- Reimplemented new helpers using old ones (Lyude)
- Reworked the drm_dp_dpcd_read_link_status() patch (Lyude)
- Dropped the dp-aux-dev patch (Jani)
- Link to v1: https://lore.kernel.org/r/20250117-drm-rework-dpcd-access-v1-0-7fc020e04dbc@linaro.org

---
Dmitry Baryshkov (7):
      drm/display: dp: implement new access helpers
      drm/display: dp: change drm_dp_dpcd_read_link_status() return value
      drm/display: dp: use new DCPD access helpers
      drm/display: dp-aux-dev: use new DCPD access helpers
      drm/display: dp-cec: use new DCPD access helpers
      drm/display: dp-mst-topology: use new DCPD access helpers
      drm/display: dp-tunnel: use new DCPD access helpers

 drivers/gpu/drm/amd/amdgpu/atombios_dp.c           |   8 +-
 .../gpu/drm/bridge/cadence/cdns-mhdp8546-core.c    |   2 +-
 drivers/gpu/drm/display/drm_dp_aux_dev.c           |  12 +-
 drivers/gpu/drm/display/drm_dp_cec.c               |  37 ++-
 drivers/gpu/drm/display/drm_dp_helper.c            | 307 +++++++++------------
 drivers/gpu/drm/display/drm_dp_mst_topology.c      | 105 ++++---
 drivers/gpu/drm/display/drm_dp_tunnel.c            |  20 +-
 drivers/gpu/drm/hisilicon/hibmc/dp/dp_link.c       |   4 +-
 drivers/gpu/drm/msm/dp/dp_ctrl.c                   |  24 +-
 drivers/gpu/drm/msm/dp/dp_link.c                   |  18 +-
 drivers/gpu/drm/radeon/atombios_dp.c               |   8 +-
 include/drm/display/drm_dp_helper.h                |  92 +++++-
 12 files changed, 322 insertions(+), 315 deletions(-)
---
base-commit: c0eb65494e59d9834af7cbad983629e9017b25a1
change-id: 20241231-drm-rework-dpcd-access-b0fc2e47d613

Best regards,
-- 
Dmitry Baryshkov <dmitry.baryshkov at linaro.org>