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

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Message-Id: <20250117-drm-rework-dpcd-access-v1-0-7fc020e04dbc@linaro.org>
Date: Fri, 17 Jan 2025 10:56:35 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, 
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, 
 Rob Clark <robdclark@...il.com>, Abhinav Kumar <quic_abhinavk@...cinc.com>, 
 Sean Paul <sean@...rly.run>, Marijn Suijten <marijn.suijten@...ainline.org>, 
 Jani Nikula <jani.nikula@...ux.intel.com>
Cc: dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org, 
 linux-arm-msm@...r.kernel.org, freedreno@...ts.freedesktop.org
Subject: [PATCH RFC 0/7] drm/display: dp: add new DPCD access functions

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@...aro.org>
---
Dmitry Baryshkov (7):
      drm/display: dp: change drm_dp_dpcd_read_link_status() return
      drm/display: dp: implement new access helpers
      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/display/drm_dp_aux_dev.c      |  12 +-
 drivers/gpu/drm/display/drm_dp_cec.c          |  37 ++-
 drivers/gpu/drm/display/drm_dp_helper.c       | 345 +++++++++++---------------
 drivers/gpu/drm/display/drm_dp_mst_topology.c | 132 +++++-----
 drivers/gpu/drm/display/drm_dp_tunnel.c       |  20 +-
 drivers/gpu/drm/msm/dp/dp_ctrl.c              |  45 ++--
 drivers/gpu/drm/msm/dp/dp_link.c              |  17 +-
 include/drm/display/drm_dp_helper.h           |  81 +++++-
 include/drm/display/drm_dp_mst_helper.h       |  10 +-
 9 files changed, 354 insertions(+), 345 deletions(-)
---
base-commit: 440aaf479c9aaf5ecea9a463eb826ec243d5f1cf
change-id: 20241231-drm-rework-dpcd-access-b0fc2e47d613

Best regards,
-- 
Dmitry Baryshkov <dmitry.baryshkov@...aro.org>