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. Implement new helpers using existing functions to ensure backwards compatibility and to assess necessity to handle incomplete reads on a global scale. Currently only one possible place has been identified, dp-aux-dev, which needs to handle possible holes in DPCD. 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@xxxxxxxxxx> --- Changes in v3: - Fixed cover letter (Jani) - Added intel-gfx and intel-xe to get the series CI-tested (Jani) - Link to v2: https://lore.kernel.org/r/20250301-drm-rework-dpcd-access-v2-0-4d92602fc7cd@xxxxxxxxxx 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@xxxxxxxxxx --- 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: 565351ae7e0cee80e9b5ed84452a5b13644ffc4d change-id: 20241231-drm-rework-dpcd-access-b0fc2e47d613 Best regards, -- Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx>
