linux-kernel - Re: [RFC PATCH RESEND v4 0/6] drm/display: dp: add new DPCD access functions

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Message-ID: <aa3ba324d1cab8fc69cce4ec0fadb567970d1878.camel@redhat.com>
Date: Mon, 24 Mar 2025 15:34:02 -0400
From: Lyude Paul <lyude@...hat.com>
To: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>, 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>, Alex Deucher <alexander.deucher@....com>, 
 Christian König	 <christian.koenig@....com>, Andrzej
 Hajda <andrzej.hajda@...el.com>, Neil Armstrong
 <neil.armstrong@...aro.org>, Robert Foss <rfoss@...nel.org>, Laurent
 Pinchart	 <Laurent.pinchart@...asonboard.com>, Jonas Karlman
 <jonas@...boo.se>, Jernej Skrabec <jernej.skrabec@...il.com>, Xinliang Liu
 <xinliang.liu@...aro.org>, Tian Tao	 <tiantao6@...ilicon.com>, Xinwei Kong
 <kong.kongxinwei@...ilicon.com>, Sumit Semwal <sumit.semwal@...aro.org>,
 Yongqin Liu <yongqin.liu@...aro.org>, John Stultz	 <jstultz@...gle.com>
Cc: dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org, 
	linux-arm-msm@...r.kernel.org, freedreno@...ts.freedesktop.org, 
	intel-gfx@...ts.freedesktop.org, intel-xe@...ts.freedesktop.org, 
	amd-gfx@...ts.freedesktop.org, Dmitry Baryshkov
 <dmitry.baryshkov@...aro.org>,  Jani Nikula <jani.nikula@...el.com>
Subject: Re: [RFC PATCH RESEND v4 0/6] drm/display: dp: add new DPCD access
 functions

This looks all good to me, do you need someone to push this to drm-misc?

On Mon, 2025-03-24 at 13:51 +0200, Dmitry Baryshkov wrote:
> 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@....qualcomm.com>
> ---
> Changes in v4:
> - Actually dropped the dp-aux-dev patch (Lyude).
> - Added two missing full stops in linuxdoc (Lyude).
> - Link to v3: https://lore.kernel.org/r/20250307-drm-rework-dpcd-access-v3-0-9044a3a868ee@linaro.org
> 
> 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@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 (6):
>       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-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_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 +++++-
>  11 files changed, 317 insertions(+), 308 deletions(-)
> ---
> base-commit: b0894e40afe2bd05d1fda68cc364665ac2b00e09
> change-id: 20241231-drm-rework-dpcd-access-b0fc2e47d613
> 
> Best regards,

-- 
Cheers,
 Lyude Paul (she/her)
 Software Engineer at Red Hat

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