linux-kernel - Re: [PATCH 0/6] drm: introduce atomic_needs

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Message-ID: <Z5ODTg9iTjNKggzN@intel.com>
Date: Fri, 24 Jan 2025 14:10:54 +0200
From: Ville Syrjälä <ville.syrjala@...ux.intel.com>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
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>,
	Dave Airlie <airlied@...hat.com>,
	Jocelyn Falempe <jfalempe@...hat.com>,
	Rob Clark <robdclark@...il.com>,
	Abhinav Kumar <quic_abhinavk@...cinc.com>,
	Sean Paul <sean@...rly.run>,
	Marijn Suijten <marijn.suijten@...ainline.org>,
	Kalyan Thota <quic_kalyant@...cinc.com>,
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
	linux-arm-msm@...r.kernel.org, freedreno@...ts.freedesktop.org,
	Simona Vetter <simona.vetter@...ll.ch>
Subject: Re: [PATCH 0/6] drm: introduce atomic_needs_modeset() callbacks

On Fri, Jan 24, 2025 at 01:14:18PM +0200, Dmitry Baryshkov wrote:
> There are several drivers which attempt to upgrading the commit to the
> full mode set from their per-object atomic_check() callbacks without
> calling the drm_atomic_helper_check_modeset() or
> drm_atomic_helper_check() again (as requested by those functions).

I don't really understand why any of that is supposedly necessary.
drm_atomic_helper_check_modeset() is really all about the
connector routing stuff, so if none of that is changing then there
is no point in calling it again. Eg. in i915 we call it just at
the start, and later on we flag internal modesets all over the
place, but none of those need drm_atomic_helper_check_modeset()
because nothing routing related will have changed.

> 
> As discussed on IRC, add separate atomic_needs_modeset() callbacks,
> whose only purpose is to allow the plane, connector, encoder or CRTC to
> specify that for whatever reasons corresponding CRTC should undergo a
> full modeset. The helpers will call these callbacks in a proper place,
> adding affected objects and calling required functions as required.
> 
> The MSM patches depend on the msm-next tree and the series at [1]. The
> plan is to land core changes through drm-misc, then merge drm-misc-next
> into msm-next and merge remaining msm-specific patches through the
> msm-next tree.
> 
> [1] https://lore.kernel.org/dri-devel/20250123-drm-dirty-modeset-v2-0-bbfd3a6cd1a4@linaro.org/
> 
> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
> ---
> Dmitry Baryshkov (6):
>       drm/atomic-helper: add atomic_needs_modeset callbacks
>       drm/mgag200: move format check to drm_plane_helper.atomic_needs_modeset
>       drm/msm/dpu: stop upgrading commits by enabling allow_modeset
>       drm/msm/dpu: move CTM check to drm_crtc_helper.atomic_needs_modeset
>       drm/msm/dpu: use atomic_needs_modeset for CDM check
>       drm/msm: drop msm_atomic_check wrapper
> 
>  drivers/gpu/drm/drm_atomic_helper.c         | 59 ++++++++++++++++++
>  drivers/gpu/drm/mgag200/mgag200_drv.h       |  2 +
>  drivers/gpu/drm/mgag200/mgag200_mode.c      | 27 ++++++---
>  drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c    | 15 +++++
>  drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c | 44 +++++++++-----
>  drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.h |  4 --
>  drivers/gpu/drm/msm/disp/dpu1/dpu_kms.c     | 26 --------
>  drivers/gpu/drm/msm/msm_atomic.c            | 29 ---------
>  drivers/gpu/drm/msm/msm_drv.h               |  1 -
>  drivers/gpu/drm/msm/msm_kms.c               |  2 +-
>  drivers/gpu/drm/msm/msm_kms.h               |  7 ---
>  include/drm/drm_modeset_helper_vtables.h    | 92 +++++++++++++++++++++++++++++
>  12 files changed, 219 insertions(+), 89 deletions(-)
> ---
> base-commit: 0936f0e54426177b0f0263ddf806ed5e13487db6
> change-id: 20250123-atomic-needs-modeset-8f6a8243a3f7
> prerequisite-change-id: 20241222-drm-dirty-modeset-88079bd27ae6:v2
> prerequisite-patch-id: 0c61aabfcd13651203f476985380cbf4d3c299e6
> prerequisite-patch-id: c6026f08011c288fd301676e9fa6f46d0cc1dab7
> prerequisite-patch-id: b0cb06d5c88791d6e4755d879ced0d5050aa3cbf
> prerequisite-patch-id: fd72ddde9dba0df053113bc505c213961a9760da
> 
> Best regards,
> -- 
> Dmitry Baryshkov <dmitry.baryshkov@...aro.org>

-- 
Ville Syrjälä
Intel