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Tue, 19 Oct 2021 07:30:51 -0700 (PDT) Received: from phenom.ffwll.local ([2a02:168:57f4:0:efd0:b9e5:5ae6:c2fa]) by smtp.gmail.com with ESMTPSA id t6sm11675493edj.27.2021.10.19.07.30.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 19 Oct 2021 07:30:51 -0700 (PDT) Date: Tue, 19 Oct 2021 16:30:49 +0200 From: Daniel Vetter To: Christian =?iso-8859-1?Q?K=F6nig?= Cc: Daniel Vetter , linaro-mm-sig@lists.linaro.org, dri-devel@lists.freedesktop.org, linux-media@vger.kernel.org, intel-gfx@lists.freedesktop.org, tvrtko.ursulin@linux.intel.com Subject: Re: [PATCH 24/28] drm: use new iterator in drm_gem_plane_helper_prepare_fb v2 Message-ID: References: <20211005113742.1101-1-christian.koenig@amd.com> <20211005113742.1101-25-christian.koenig@amd.com> <405b9df8-58fd-b8f2-cec2-acde69aa5633@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <405b9df8-58fd-b8f2-cec2-acde69aa5633@gmail.com> X-Operating-System: Linux phenom 5.10.0-8-amd64 Precedence: bulk List-ID: X-Mailing-List: linux-media@vger.kernel.org On Tue, Oct 19, 2021 at 03:02:26PM +0200, Christian König wrote: > Am 13.10.21 um 16:23 schrieb Daniel Vetter: > > On Tue, Oct 05, 2021 at 01:37:38PM +0200, Christian König wrote: > > > Makes the handling a bit more complex, but avoids the use of > > > dma_resv_get_excl_unlocked(). > > > > > > v2: improve coding and documentation > > > > > > Signed-off-by: Christian König > > > --- > > > drivers/gpu/drm/drm_gem_atomic_helper.c | 13 +++++++++++-- > > > 1 file changed, 11 insertions(+), 2 deletions(-) > > > > > > diff --git a/drivers/gpu/drm/drm_gem_atomic_helper.c b/drivers/gpu/drm/drm_gem_atomic_helper.c > > > index e570398abd78..8534f78d4d6d 100644 > > > --- a/drivers/gpu/drm/drm_gem_atomic_helper.c > > > +++ b/drivers/gpu/drm/drm_gem_atomic_helper.c > > > @@ -143,6 +143,7 @@ > > > */ > > > int drm_gem_plane_helper_prepare_fb(struct drm_plane *plane, struct drm_plane_state *state) > > > { > > > + struct dma_resv_iter cursor; > > > struct drm_gem_object *obj; > > > struct dma_fence *fence; > > > @@ -150,9 +151,17 @@ int drm_gem_plane_helper_prepare_fb(struct drm_plane *plane, struct drm_plane_st > > > return 0; > > > obj = drm_gem_fb_get_obj(state->fb, 0); > > > - fence = dma_resv_get_excl_unlocked(obj->resv); > > > - drm_atomic_set_fence_for_plane(state, fence); > > > + dma_resv_iter_begin(&cursor, obj->resv, false); > > > + dma_resv_for_each_fence_unlocked(&cursor, fence) { > > > + /* TODO: We only use the first write fence here and need to fix > > > + * the drm_atomic_set_fence_for_plane() API to accept more than > > > + * one. */ > > I'm confused, right now there is only one write fence. So no need to > > iterate, and also no need to add a TODO. If/when we add more write fences > > then I think this needs to be revisited, and ofc then we do need to update > > the set_fence helpers to carry an entire array of fences. > > Well could be that I misunderstood you, but in your last explanation it > sounded like the drm_atomic_set_fence_for_plane() function needs fixing > anyway because a plane could have multiple BOs. > > So in my understanding what we need is a > drm_atomic_add_dependency_for_plane() function which records that a certain > fence needs to be signaled before a flip. Yeah that's another issue, but in practice there's no libva which decodes into planar yuv with different fences between the planes. So not a bug in practice. But this is entirely orthogonal to you picking up the wrong fence here if there's not exclusive fence set: - old code: Either pick the exclusive fence, or not fence if the exclusive one is not set. - new code: Pick the exclusive fence or the first shared fence New behaviour is busted, because scanning out and reading from a buffer at the same time (for the next frame, e.g. to copy over damaged areas or some other tricks) is very much a supported thing. Atomic _only_ wants to look at the exclusive fence slot, which mean "there is an implicitly synced write to this buffers". Implicitly synced reads _must_ be ignored. Now amdgpu doesn't have this distinction in its uapi, but many drivers do. -Daniel > Support for more than one write fence then comes totally naturally. > > Christian. > > > -Daniel > > > > > + dma_fence_get(fence); > > > + break; > > > + } > > > + dma_resv_iter_end(&cursor); > > > + drm_atomic_set_fence_for_plane(state, fence); > > > return 0; > > > } > > > EXPORT_SYMBOL_GPL(drm_gem_plane_helper_prepare_fb); > > > -- > > > 2.25.1 > > > > -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch