| Message ID | 1398241805-24564-1-git-send-email-daniel.vetter@ffwll.ch (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Wed, Apr 23, 2014 at 10:30:04AM +0200, Daniel Vetter wrote: > The introduction of primary planes has apparently caused a bit of fb > refcounting fun for people. That makes it a good time to clean up the > arcane rules and slight differences between ->update_plane and > ->set_config. The new rules are: > > - The core holds a reference for both the new and the old fb (if > they're non-NULL of course) while calling into the driver through > either ->update_plane or ->set_config. > > - Drivers may not clobber plane->fb if their callback fails. If they > do that, they need to store a pointer to the old fb in it again. > When calling into the driver plane->fb still points at the current > (old) framebuffer. > > - The core will update the plane->fb pointer on success. Drivers can > do that themselves too, but aren't required to any more for the > primary plane. > > - The core will update fb refcounts for the plane->fb pointer, > presuming the drivers hold up their end of the bargain. > > v2: Remove now unused tmpfb (Thierry) > > v3: Drop broken changes from drm_mode_setplane (Ville). Also polish > the commit message a bit. > > v4: Also fix up the handling of ->disable_plane in > drm_plane_force_disable. The issue was that we didn't save plane->fb > over the ->disable_plane call. Just paranoia, nothing relies on this. > > Cc: Thierry Reding <treding@nvidia.com> > Cc: Ville Syrjälä <ville.syrjala@linux.intel.com> > Cc: Matt Roper <matthew.d.roper@intel.com> > Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch> > --- > drivers/gpu/drm/drm_crtc.c | 13 +++++++------ > drivers/gpu/drm/drm_plane_helper.c | 16 ---------------- > 2 files changed, 7 insertions(+), 22 deletions(-) > > diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c > index d8b7099abece..f6633cb927bc 100644 > --- a/drivers/gpu/drm/drm_crtc.c > +++ b/drivers/gpu/drm/drm_crtc.c > @@ -1145,16 +1145,17 @@ EXPORT_SYMBOL(drm_plane_cleanup); > */ > void drm_plane_force_disable(struct drm_plane *plane) > { > + struct drm_framebuffer *old_fb = plane->fb; > int ret; > > - if (!plane->fb) > + if (!old_fb) > return; > > ret = plane->funcs->disable_plane(plane); > if (ret) > DRM_ERROR("failed to disable plane with busy fb\n"); > /* disconnect the plane from the fb and crtc: */ > - __drm_framebuffer_unreference(plane->fb); > + __drm_framebuffer_unreference(old_fb); > plane->fb = NULL; > plane->crtc = NULL; > } So if disable_plane() fails here, we'd still be scanning out of old_fb, yet we deref it...that doesn't seem quite right. As you mention, the changes here are just for paranoia since we can't hit failure here as far as I know; force_disable() is only called in drm_framebuffer_remove() (where a CRTC loop has already taken care of removing the framebuffer from the primary plane) and drm_fb_helper_restore_fbdev_mode() (where we explicitly skip primary planes). Since only primary planes can fail to be disabled, I'd be inclined to just add a BUG_ON(plane->type == DRM_PLANE_TYPE_PRIMARY) at the start of this function with a comment update explaining that it can't be called on primary planes, and a BUG_ON(ret) since non-primary planes should never fail to be disabled. ... > @@ -177,22 +176,7 @@ int drm_primary_helper_update(struct drm_plane *plane, struct drm_crtc *crtc, > set.connectors = connector_list; > set.num_connectors = num_connectors; > > - /* > - * set_config() adjusts crtc->primary->fb; however the DRM setplane > - * code that called us expects to handle the framebuffer update and > - * reference counting; save and restore the current fb before > - * calling it. > - * > - * N.B., we call set_config() directly here rather than using > - * drm_mode_set_config_internal. We're reprogramming the same > - * connectors that were already in use, so we shouldn't need the extra > - * cross-CRTC fb refcounting to accomodate stealing connectors. > - * drm_mode_setplane() already handles the basic refcounting for the > - * framebuffers involved in this operation. > - */ I think the second half of this comment (explaining why we call set_config() directly rather than calling drm_mode_set_config_internal()) still has some value. Matt > - tmpfb = plane->fb; > ret = crtc->funcs->set_config(&set); > - plane->fb = tmpfb; > > kfree(connector_list); > return ret; > -- > 1.9.2 >
On Wed, Apr 23, 2014 at 4:45 PM, Matt Roper <matthew.d.roper@intel.com> wrote: >> @@ -177,22 +176,7 @@ int drm_primary_helper_update(struct drm_plane *plane, struct drm_crtc *crtc, >> set.connectors = connector_list; >> set.num_connectors = num_connectors; >> >> - /* >> - * set_config() adjusts crtc->primary->fb; however the DRM setplane >> - * code that called us expects to handle the framebuffer update and >> - * reference counting; save and restore the current fb before >> - * calling it. >> - * >> - * N.B., we call set_config() directly here rather than using >> - * drm_mode_set_config_internal. We're reprogramming the same >> - * connectors that were already in use, so we shouldn't need the extra >> - * cross-CRTC fb refcounting to accomodate stealing connectors. >> - * drm_mode_setplane() already handles the basic refcounting for the >> - * framebuffers involved in this operation. >> - */ > > I think the second half of this comment (explaining why we call > set_config() directly rather than calling > drm_mode_set_config_internal()) still has some value. Sorry I've forgotten to keep it when respinning the patch. I agree with you. Will resend. -Daniel
diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c index d8b7099abece..f6633cb927bc 100644 --- a/drivers/gpu/drm/drm_crtc.c +++ b/drivers/gpu/drm/drm_crtc.c @@ -1145,16 +1145,17 @@ EXPORT_SYMBOL(drm_plane_cleanup); */ void drm_plane_force_disable(struct drm_plane *plane) { + struct drm_framebuffer *old_fb = plane->fb; int ret; - if (!plane->fb) + if (!old_fb) return; ret = plane->funcs->disable_plane(plane); if (ret) DRM_ERROR("failed to disable plane with busy fb\n"); /* disconnect the plane from the fb and crtc: */ - __drm_framebuffer_unreference(plane->fb); + __drm_framebuffer_unreference(old_fb); plane->fb = NULL; plane->crtc = NULL; } @@ -2187,16 +2188,18 @@ int drm_mode_setplane(struct drm_device *dev, void *data, } drm_modeset_lock_all(dev); + old_fb = plane->fb; ret = plane->funcs->update_plane(plane, crtc, fb, plane_req->crtc_x, plane_req->crtc_y, plane_req->crtc_w, plane_req->crtc_h, plane_req->src_x, plane_req->src_y, plane_req->src_w, plane_req->src_h); if (!ret) { - old_fb = plane->fb; plane->crtc = crtc; plane->fb = fb; fb = NULL; + } else { + old_fb = NULL; } drm_modeset_unlock_all(dev); @@ -2239,9 +2242,7 @@ int drm_mode_set_config_internal(struct drm_mode_set *set) ret = crtc->funcs->set_config(set); if (ret == 0) { crtc->primary->crtc = crtc; - - /* crtc->fb must be updated by ->set_config, enforces this. */ - WARN_ON(fb != crtc->primary->fb); + crtc->primary->fb = fb; } list_for_each_entry(tmp, &crtc->dev->mode_config.crtc_list, head) { diff --git a/drivers/gpu/drm/drm_plane_helper.c b/drivers/gpu/drm/drm_plane_helper.c index 9540ff9f97fe..b72736d5541d 100644 --- a/drivers/gpu/drm/drm_plane_helper.c +++ b/drivers/gpu/drm/drm_plane_helper.c @@ -124,7 +124,6 @@ int drm_primary_helper_update(struct drm_plane *plane, struct drm_crtc *crtc, .y2 = crtc->mode.vdisplay, }; struct drm_connector **connector_list; - struct drm_framebuffer *tmpfb; int num_connectors, ret; if (!crtc->enabled) { @@ -177,22 +176,7 @@ int drm_primary_helper_update(struct drm_plane *plane, struct drm_crtc *crtc, set.connectors = connector_list; set.num_connectors = num_connectors; - /* - * set_config() adjusts crtc->primary->fb; however the DRM setplane - * code that called us expects to handle the framebuffer update and - * reference counting; save and restore the current fb before - * calling it. - * - * N.B., we call set_config() directly here rather than using - * drm_mode_set_config_internal. We're reprogramming the same - * connectors that were already in use, so we shouldn't need the extra - * cross-CRTC fb refcounting to accomodate stealing connectors. - * drm_mode_setplane() already handles the basic refcounting for the - * framebuffers involved in this operation. - */ - tmpfb = plane->fb; ret = crtc->funcs->set_config(&set); - plane->fb = tmpfb; kfree(connector_list); return ret;
The introduction of primary planes has apparently caused a bit of fb refcounting fun for people. That makes it a good time to clean up the arcane rules and slight differences between ->update_plane and ->set_config. The new rules are: - The core holds a reference for both the new and the old fb (if they're non-NULL of course) while calling into the driver through either ->update_plane or ->set_config. - Drivers may not clobber plane->fb if their callback fails. If they do that, they need to store a pointer to the old fb in it again. When calling into the driver plane->fb still points at the current (old) framebuffer. - The core will update the plane->fb pointer on success. Drivers can do that themselves too, but aren't required to any more for the primary plane. - The core will update fb refcounts for the plane->fb pointer, presuming the drivers hold up their end of the bargain. v2: Remove now unused tmpfb (Thierry) v3: Drop broken changes from drm_mode_setplane (Ville). Also polish the commit message a bit. v4: Also fix up the handling of ->disable_plane in drm_plane_force_disable. The issue was that we didn't save plane->fb over the ->disable_plane call. Just paranoia, nothing relies on this. Cc: Thierry Reding <treding@nvidia.com> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com> Cc: Matt Roper <matthew.d.roper@intel.com> Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch> --- drivers/gpu/drm/drm_crtc.c | 13 +++++++------ drivers/gpu/drm/drm_plane_helper.c | 16 ---------------- 2 files changed, 7 insertions(+), 22 deletions(-)