From mboxrd@z Thu Jan 1 00:00:00 1970 From: Laurent Pinchart Subject: Re: [PATCH 1/4] drm/atomic: implement drm_atomic_helper_commit_tail for runtime_pm users Date: Tue, 18 Jul 2017 13:14:12 +0300 Message-ID: <10955632.YI7NJnTkKU@avalon> References: <1823154.LT2zYSFJ4j@avalon> <20170718070522.6uu7s6o3ivpemslf@flea> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7Bit Return-path: In-Reply-To: <20170718070522.6uu7s6o3ivpemslf@flea> Sender: linux-kernel-owner@vger.kernel.org To: Maxime Ripard Cc: Daniel Vetter , David Airlie , Jani Nikula , Sean Paul , Inki Dae , Joonyoung Shim , Seung-Woo Kim , Kyungmin Park , Kukjin Kim , Krzysztof Kozlowski , Mark Yao , Heiko Stuebner , Chen-Yu Tsai , dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-samsung-soc@vger.kernel.org, linux-renesas-soc@vger.kernel.org, linux-rockchip@lists.infradead.org List-Id: dri-devel@lists.freedesktop.org Hi Maxime, On Tuesday 18 Jul 2017 09:05:22 Maxime Ripard wrote: > On Fri, Jul 14, 2017 at 02:43:12AM +0300, Laurent Pinchart wrote: > > 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 > >> --- > >> > >> 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. > > I will. > > > 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. > > I'm not sure it would apply. Our driver doesn't use runtime_pm at all, > but in order for the commits to happen, we need to have the CRTC > active, but it will remain powered up the whole time. I'm not sure if > we'll ever see such a frame. > > But since this seems to be a pretty generic, maybe we should address > it in the helper itself? I think that would make sense. There are a few options that result in too many combinations for separate commit tail helpers to be provided in my opinion: - disable/enable/planes vs. disable/planes/enable - DRM_PLANE_COMMIT_ACTIVE_ONLY vs. all CRTCs - drm_atomic_helper_wait_for_vblanks vs drm_atomic_helper_wait_for_flip_done Maybe we could add a few CRTC commit helper flags along the line of DRM_PLANE_COMMIT_ACTIVE_ONLY, add a field to the drm_crtc structure to store them, and have drm_atomic_helper_commit_tail() use those flags to control the sequence of operations. -- Regards, Laurent Pinchart