Messages in this thread | | | From | Laurent Pinchart <> | Subject | Re: [PATCH 1/4] drm/atomic: implement drm_atomic_helper_commit_tail for runtime_pm users | Date | Fri, 14 Jul 2017 02:43:12 +0300 |
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Hi Maxime,
Thank you for the patch.
On Thursday 13 Jul 2017 16:41:13 Maxime Ripard wrote: > The current drm_atomic_helper_commit_tail helper works only if the CRTC is > accessible, and documents an alternative implementation that is supposed to > be used if that happens. > > That implementation is then duplicated by some drivers. Instead of > documenting it, let's implement an helper that all the relevant users can > use directly. > > Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com> > --- > drivers/gpu/drm/drm_atomic_helper.c | 47 +++++++++++++++-------- > drivers/gpu/drm/exynos/exynos_drm_fb.c | 27 +------------- > drivers/gpu/drm/rcar-du/rcar_du_kms.c | 18 +---------
I've submitted "[PATCH] drm: rcar-du: Setup planes before enabling CRTC to avoid flicker" that changes the rcar-du implementation to the standard disable/update planes/enable order, so I'd appreciate if you could drop the rcar-du part of this patch to avoid conflicts.
This being said, the reason why I switched back from the "runtime PM" to the "standard" order is probably of interest to you. Quoting the commit message,
> Commit 52055bafa1ff ("drm: rcar-du: Move plane commit code from CRTC > start to CRTC resume") changed the order of the plane commit and CRTC > enable operations to accommodate the runtime PM requirements. However, > this introduced corruption in the first displayed frame, as the CRTC is > now enabled without any plane configured. On Gen2 hardware the first > frame will be black and likely unnoticed, but on Gen3 hardware we end up > starting the display before the VSP compositor, which is more > noticeable. > > To fix this, revert the order of the commit operations back, and handle > runtime PM requirements in the CRTC .atomic_begin() and .atomic_enable() > helper operation handlers.
I believe that the "runtime PM" order is problematic in most drivers. The problem usually goes unnoticed as most monitors will not even display the first frame, and I assume many devices will just output it black, but it's an issue nonetheless.
Note that my driver hasn't lost the "runtime PM" requirements, so I had to support them with the "standard" order. The best way I've found was to runtime resume in the one of .atomic_begin() and .enable() that is run first. Not very neat, as similar code would be needed in most drivers. I wonder whether it wouldn't be useful to add resume/suspend helper callbacks for the CRTC.
> drivers/gpu/drm/rockchip/rockchip_drm_fb.c | 21 +---------- > include/drm/drm_atomic_helper.h | 1 +- > 5 files changed, 36 insertions(+), 78 deletions(-)
-- Regards,
Laurent Pinchart
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