| Message ID | 1473857701-9250-3-git-send-email-tfiga@chromium.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 2016年09月14日 20:54, Tomasz Figa wrote: > Current code implements prepare_fb and cleanup_fb callbacks only to > grab/release fb references, which is already done by atomic framework > when creating/destryoing plane state. Let's remove these > unused bits. > > Signed-off-by: Tomasz Figa <tfiga@chromium.org> > --- > drivers/gpu/drm/rockchip/rockchip_drm_vop.c | 18 ------------------ > 1 file changed, 18 deletions(-) Hi Tomasz I think we can't get rid of the prepare_fb and cleanup_fb see the reason: commit 44d0237a26395ac94160cf23f32769013b365590 Author: Mark Yao <mark.yao@rock-chips.com> Date: Fri Apr 29 11:37:20 2016 +0800 drm/rockchip: vop: fix iommu crash with async atomic After async atomic_commit callback, drm_atomic_clean_old_fb will clean all old fb, but because async, the old fb may be also on the vop hardware, dma will access the old fb buffer, clean old fb will cause iommu page fault. Reference the fb and unreference it when the fb actuall swap out from vop hardware. > diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_vop.c b/drivers/gpu/drm/rockchip/rockchip_drm_vop.c > index 7e811cf..68988c6 100644 > --- a/drivers/gpu/drm/rockchip/rockchip_drm_vop.c > +++ b/drivers/gpu/drm/rockchip/rockchip_drm_vop.c > @@ -641,22 +641,6 @@ static void vop_plane_destroy(struct drm_plane *plane) > drm_plane_cleanup(plane); > } > > -static int vop_plane_prepare_fb(struct drm_plane *plane, > - struct drm_plane_state *new_state) > -{ > - if (plane->state->fb) > - drm_framebuffer_reference(plane->state->fb); > - > - return 0; > -} > - > -static void vop_plane_cleanup_fb(struct drm_plane *plane, > - struct drm_plane_state *old_state) > -{ > - if (old_state->fb) > - drm_framebuffer_unreference(old_state->fb); > -} > - > static int vop_plane_atomic_check(struct drm_plane *plane, > struct drm_plane_state *state) > { > @@ -849,8 +833,6 @@ static void vop_plane_atomic_update(struct drm_plane *plane, > } > > static const struct drm_plane_helper_funcs plane_helper_funcs = { > - .prepare_fb = vop_plane_prepare_fb, > - .cleanup_fb = vop_plane_cleanup_fb, > .atomic_check = vop_plane_atomic_check, > .atomic_update = vop_plane_atomic_update, > .atomic_disable = vop_plane_atomic_disable,
Hi Mark, On Sun, Sep 18, 2016 at 10:50 AM, Mark yao <mark.yao@rock-chips.com> wrote: > On 2016年09月14日 20:54, Tomasz Figa wrote: >> >> Current code implements prepare_fb and cleanup_fb callbacks only to >> grab/release fb references, which is already done by atomic framework >> when creating/destryoing plane state. Let's remove these >> unused bits. >> >> Signed-off-by: Tomasz Figa <tfiga@chromium.org> >> --- >> drivers/gpu/drm/rockchip/rockchip_drm_vop.c | 18 ------------------ >> 1 file changed, 18 deletions(-) > > > Hi Tomasz > > I think we can't get rid of the prepare_fb and cleanup_fb I think I have to disagree. Please see below for detailed explanation. > > see the reason: > commit 44d0237a26395ac94160cf23f32769013b365590 > Author: Mark Yao <mark.yao@rock-chips.com> > Date: Fri Apr 29 11:37:20 2016 +0800 > > drm/rockchip: vop: fix iommu crash with async atomic > > After async atomic_commit callback, drm_atomic_clean_old_fb will > clean all old fb, but because async, the old fb may be also on > the vop hardware, dma will access the old fb buffer, clean old > fb will cause iommu page fault. I think the above is not quite right. Atomic plane state holds a reference to its fb and old state is not supposed to be destroyed until the flip completes. Indeed current rockchip_atomic_commit implementation has following order of calls: rockchip_atomic_wait_for_complete(), drm_atomic_helper_cleanup_planes(), drm_atomic_state_free(). This means that .cleanup_fb() is called from drm_atomic_helper_cleanup_planes() just before drm_atomic_state_free() will release references by destroying old plane states. Note that both are called already after rockchip_atomic_wait_for_complete(), so it should be already safe to free the old fbs. So the above fix doesn't really do anything, possibly just covers the race condition of the original wait for vblank function by delaying drm_atomic_state_free() a bit. Moreover, the whole series has been thoroughly tested in Chrome OS 4.4 kernel, including async commits. (There is still a possibility some newer upstream changes slightly modified the semantics, but I couldn't find such difference. Actually one of the advantages of atomic helpers was to avoid manually refcounting the fbs from the driver.) Best regards, Tomasz
On 2016年09月18日 12:01, Tomasz Figa wrote: > Hi Mark, > > On Sun, Sep 18, 2016 at 10:50 AM, Mark yao <mark.yao@rock-chips.com> wrote: >> On 2016年09月14日 20:54, Tomasz Figa wrote: >>> Current code implements prepare_fb and cleanup_fb callbacks only to >>> grab/release fb references, which is already done by atomic framework >>> when creating/destryoing plane state. Let's remove these >>> unused bits. >>> >>> Signed-off-by: Tomasz Figa <tfiga@chromium.org> >>> --- >>> drivers/gpu/drm/rockchip/rockchip_drm_vop.c | 18 ------------------ >>> 1 file changed, 18 deletions(-) >> >> Hi Tomasz >> >> I think we can't get rid of the prepare_fb and cleanup_fb > I think I have to disagree. Please see below for detailed explanation. > >> see the reason: >> commit 44d0237a26395ac94160cf23f32769013b365590 >> Author: Mark Yao <mark.yao@rock-chips.com> >> Date: Fri Apr 29 11:37:20 2016 +0800 >> >> drm/rockchip: vop: fix iommu crash with async atomic >> >> After async atomic_commit callback, drm_atomic_clean_old_fb will >> clean all old fb, but because async, the old fb may be also on >> the vop hardware, dma will access the old fb buffer, clean old >> fb will cause iommu page fault. > I think the above is not quite right. Atomic plane state holds a > reference to its fb and old state is not supposed to be destroyed > until the flip completes. > > Indeed current rockchip_atomic_commit implementation has following > order of calls: rockchip_atomic_wait_for_complete(), > drm_atomic_helper_cleanup_planes(), drm_atomic_state_free(). This > means that .cleanup_fb() is called from > drm_atomic_helper_cleanup_planes() just before drm_atomic_state_free() > will release references by destroying old plane states. Note that both > are called already after rockchip_atomic_wait_for_complete(), so it > should be already safe to free the old fbs. > > So the above fix doesn't really do anything, possibly just covers the > race condition of the original wait for vblank function by delaying > drm_atomic_state_free() a bit. > > Moreover, the whole series has been thoroughly tested in Chrome OS 4.4 > kernel, including async commits. (There is still a possibility some > newer upstream changes slightly modified the semantics, but I couldn't > find such difference. Actually one of the advantages of atomic helpers > was to avoid manually refcounting the fbs from the driver.) > > Best regards, > Tomasz > Hi Tomasz You are right, plane_duplicate_state/plane_destroy_state already protect the old fbs. we can get rid of prepare_fb and cleanup_fb.
diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_vop.c b/drivers/gpu/drm/rockchip/rockchip_drm_vop.c index 7e811cf..68988c6 100644 --- a/drivers/gpu/drm/rockchip/rockchip_drm_vop.c +++ b/drivers/gpu/drm/rockchip/rockchip_drm_vop.c @@ -641,22 +641,6 @@ static void vop_plane_destroy(struct drm_plane *plane) drm_plane_cleanup(plane); } -static int vop_plane_prepare_fb(struct drm_plane *plane, - struct drm_plane_state *new_state) -{ - if (plane->state->fb) - drm_framebuffer_reference(plane->state->fb); - - return 0; -} - -static void vop_plane_cleanup_fb(struct drm_plane *plane, - struct drm_plane_state *old_state) -{ - if (old_state->fb) - drm_framebuffer_unreference(old_state->fb); -} - static int vop_plane_atomic_check(struct drm_plane *plane, struct drm_plane_state *state) { @@ -849,8 +833,6 @@ static void vop_plane_atomic_update(struct drm_plane *plane, } static const struct drm_plane_helper_funcs plane_helper_funcs = { - .prepare_fb = vop_plane_prepare_fb, - .cleanup_fb = vop_plane_cleanup_fb, .atomic_check = vop_plane_atomic_check, .atomic_update = vop_plane_atomic_update, .atomic_disable = vop_plane_atomic_disable,
Current code implements prepare_fb and cleanup_fb callbacks only to grab/release fb references, which is already done by atomic framework when creating/destryoing plane state. Let's remove these unused bits. Signed-off-by: Tomasz Figa <tfiga@chromium.org> --- drivers/gpu/drm/rockchip/rockchip_drm_vop.c | 18 ------------------ 1 file changed, 18 deletions(-)