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Thu, 19 Nov 2020 07:32:19 -0800 (PST) Date: Thu, 19 Nov 2020 16:32:17 +0100 From: Daniel Vetter To: Thomas Zimmermann Subject: Re: [PATCH 1/8] drm: Introduce an atomic_commit_setup function Message-ID: <20201119153217.GE401619@phenom.ffwll.local> References: <20201113152956.139663-1-maxime@cerno.tech> <20201113152956.139663-2-maxime@cerno.tech> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-Operating-System: Linux phenom 5.7.0-1-amd64 X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mark Rutland , devicetree@vger.kernel.org, Tim Gover , Dave Stevenson , David Airlie , Daniel Vetter , dri-devel@lists.freedesktop.org, Rob Herring , bcm-kernel-feedback-list@broadcom.com, Maxime Ripard , Daniel Vetter , Frank Rowand , Phil Elwell , linux-arm-kernel@lists.infradead.org, linux-rpi-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" On Thu, Nov 19, 2020 at 10:59:42AM +0100, Thomas Zimmermann wrote: > Hi > > Am 13.11.20 um 16:29 schrieb Maxime Ripard: > > Private objects storing a state shared across all CRTCs need to be > > carefully handled to avoid a use-after-free issue. > > > > The proper way to do this to track all the commits using that shared > > state and wait for the previous commits to be done before going on with > > the current one to avoid the reordering of commits that could occur. > > > > However, this commit setup needs to be done after > > drm_atomic_helper_setup_commit(), because before the CRTC commit > > structure hasn't been allocated before, and before the workqueue is > > scheduled, because we would be potentially reordered already otherwise. > > > > That means that drivers currently have to roll their own > > drm_atomic_helper_commit() function, even though it would be identical > > if not for the commit setup. > > > > Let's introduce a hook to do so that would be called as part of > > drm_atomic_helper_commit, allowing us to reuse the atomic helpers. > > > > Suggested-by: Daniel Vetter > > Signed-off-by: Maxime Ripard > > --- > > drivers/gpu/drm/drm_atomic_helper.c | 6 ++++++ > > include/drm/drm_modeset_helper_vtables.h | 18 ++++++++++++++++++ > > 2 files changed, 24 insertions(+) > > > > diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c > > index ddd0e3239150..7d69c7844dfc 100644 > > --- a/drivers/gpu/drm/drm_atomic_helper.c > > +++ b/drivers/gpu/drm/drm_atomic_helper.c > > @@ -2083,8 +2083,11 @@ int drm_atomic_helper_setup_commit(struct drm_atomic_state *state, > > struct drm_plane *plane; > > struct drm_plane_state *old_plane_state, *new_plane_state; > > struct drm_crtc_commit *commit; > > + const struct drm_mode_config_helper_funcs *funcs; > > int i, ret; > > + funcs = state->dev->mode_config.helper_private; > > + > > for_each_oldnew_crtc_in_state(state, crtc, old_crtc_state, new_crtc_state, i) { > > commit = kzalloc(sizeof(*commit), GFP_KERNEL); > > if (!commit) > > @@ -2169,6 +2172,9 @@ int drm_atomic_helper_setup_commit(struct drm_atomic_state *state, > > new_plane_state->commit = drm_crtc_commit_get(commit); > > } > > + if (funcs && funcs->atomic_commit_setup) > > + return funcs->atomic_commit_setup(state); > > + > > return 0; > > } > > EXPORT_SYMBOL(drm_atomic_helper_setup_commit); > > diff --git a/include/drm/drm_modeset_helper_vtables.h b/include/drm/drm_modeset_helper_vtables.h > > index f2de050085be..56470baf0513 100644 > > --- a/include/drm/drm_modeset_helper_vtables.h > > +++ b/include/drm/drm_modeset_helper_vtables.h > > @@ -1396,6 +1396,24 @@ struct drm_mode_config_helper_funcs { > > * drm_atomic_helper_commit_tail(). > > */ > > void (*atomic_commit_tail)(struct drm_atomic_state *state); > > + > > + /** > > + * @atomic_commit_setup: > > + * > > + * This hook is used by the default atomic_commit() hook implemented in > > + * drm_atomic_helper_commit() together with the nonblocking helpers (see > > + * drm_atomic_helper_setup_commit()) to extend the DRM commit setup. It > > + * is not used by the atomic helpers. > > + * > > + * This function is called at the end of > > + * drm_atomic_helper_setup_commit(), so once the commit has been > > + * properly setup across the generic DRM object states. It allows > > + * drivers to do some additional commit tracking that isn't related to a > > + * CRTC, plane or connector, typically a private object. > > + * > > + * This hook is optional. > > + */ > > + int (*atomic_commit_setup)(struct drm_atomic_state *state); > > It feels hacky and screwed-on to me. I'd suggest to add an > atomic_commit_prepare callback that is called by drm_atomic_helper where it > currently calls drm_atomic_helper_setup_commit(). The default implementation > would include setup_commit and prepare_planes. Some example code for > drm_atomic_helper.c > > static int commit_prepare(state) > { > drm_atomic_helper_setup_commit(state) > > drm_atomic_helper_prepare_planes(state) > } > > int drm_atomic_helper_commit() > { > if (async_update) { > ... > } > > if (funcs->atomic_commit_prepare) > funcs->atomic_commit_prepare(state) > else > commit_prepare(state) > > /* the rest of the current function below */ > INIT_WORK(&state->commit_work, commit_work); > ... > } > > Drivers that implement atomic_commit_prepare would be expected to call > drm_atomic_helper_setup_commit() and drm_atomic_helper_prepare_planes() or > their own implementation of them. > > The whole construct mimics how commit tails work. Yeah what I suggested is a bit much midlayer, but we've done what you suggested above with all drivers rolling their own atomic_commit. It wasn't pretty. There's still drivers like vc4 which haven't switched, and which have their own locking and synchronization. Hence why I think the callback approach here is better, gives drivers less excuses to roll their own and make a mess. -Daniel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch _______________________________________________ dri-devel mailing list dri-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/dri-devel