On Tue, Apr 22, 2014 at 01:06:22PM +0300, Ville Syrjälä wrote:
> On Tue, Apr 22, 2014 at 11:07:13AM +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 their
> > 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.
> >
> > - The core will update fb refcounts for the plane->fb pointer,
> > presuming the drivers hold up their end of the bargain.
> >
> > Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
> > ---
> > drivers/gpu/drm/drm_crtc.c | 12 +++++-------
> > drivers/gpu/drm/drm_plane_helper.c | 15 ---------------
> > 2 files changed, 5 insertions(+), 22 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
> > index d8b7099abece..966b480ed543 100644
> > --- a/drivers/gpu/drm/drm_crtc.c
> > +++ b/drivers/gpu/drm/drm_crtc.c
> > @@ -2187,24 +2187,24 @@ 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;
> > }
> > drm_modeset_unlock_all(dev);
> >
> > out:
> > - if (fb)
> > - drm_framebuffer_unreference(fb);
> > + if (plane->fb)
> > + drm_framebuffer_reference(old_fb);
> ^^^^^^
>
> That doesn't look right.
>
> Also you're now dereferencing plane->fb after you drop the locks.
Oops, will fix.
> Also i915 fb destruction seems buggy as we do
> intel_fb->obj->framebuffer_references-- w/o holding struct_mutex.
Hm, this indeed looks fishy. And the offending patch was actually r-b:
you. Not sure what to do here really.
-Daniel
>
> > if (old_fb)
> > drm_framebuffer_unreference(old_fb);
> > + drm_framebuffer_unreference(fb);
> >
> > return ret;
> > }
> > @@ -2239,9 +2239,7 @@ 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 e768d35ff22e..8db129c44fea 100644
> > --- a/drivers/gpu/drm/drm_plane_helper.c
> > +++ b/drivers/gpu/drm/drm_plane_helper.c
> > @@ -175,22 +175,7 @@ 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;
> > --
> > 1.9.2
> >
> > _______________________________________________
> > dri-devel mailing list
> > dri-devel@xxxxxxxxxxxxxxxxxxxxx
> > http://lists.freedesktop.org/mailman/listinfo/dri-devel
>
> --
> Ville Syrjälä
> Intel OTC
--
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
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