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

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Message-ID: <pxcgcutzjjge6ruw5hobg6jkfqozhtlvbhdlmyazesbi4aipj2@enepqlcvjruw>
Date: Sun, 9 Feb 2025 05:38:17 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Jani Nikula <jani.nikula@...ux.intel.com>
Cc: 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>, dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org, 
	linux-arm-msm@...r.kernel.org, freedreno@...ts.freedesktop.org
Subject: Re: [PATCH RFC 0/7] drm/display: dp: add new DPCD access functions

On Thu, Jan 23, 2025 at 12:12:43PM +0200, Jani Nikula wrote:
> On Thu, 23 Jan 2025, Dmitry Baryshkov <dmitry.baryshkov@...aro.org> wrote:
> > On Fri, Jan 17, 2025 at 10:56:35AM +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. 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.
> >
> > Gracious ping for the series, it's been posted a week ago.
> 
> It's a bit of a bummer the names become longer. I don't have a better
> suggestion, though.
> 
> I do like it that the error handling becomes easier and more uniform
> overall, and this actually fixes many places that only checked for < 0
> with the old functions.
> 
> I glanced through the series, I didn't spot anything obviously wrong,
> but didn't do a thorough review either. I can do once we have wider
> buy-in for the idea in general, so the effort won't be wasted.
> 
> For now,
> 
> Acked-by: Jani Nikula <jani.nikula@...el.com>

Is it okay to merge this? I'd prefer to have comments from other
developers / maintainers, so that it doesn't become a controversial
change.

> >> 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>
> >> 
> 
> -- 
> Jani Nikula, Intel

-- 
With best wishes
Dmitry