On Tue, Apr 22, 2014 at 04:19:45PM +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.
It looks like we might have some problems around setplane with fbid=0.
It looks like we're assuming that disabling a plane always succeeds
(which is no longer true for helper-based primary planes --- they just
return -EINVAL on disable now), so we wind up setting old_fb to the
currently scanned out framebuffer and then unref it at the end of the
function if I'm reading things correctly. We also clobber the
plane->crtc and plane->fb pointers too when this happens.
I think the real problem here was introduced on b6ccd7b9 and I gave you
an r-b tag on that email, so that's my bad for not catching it before.
:-(
Matt
>
> Cc: Thierry Reding <treding@xxxxxxxxxx>
> Cc: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
> Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
> ---
> drivers/gpu/drm/drm_crtc.c | 8 ++++----
> drivers/gpu/drm/drm_plane_helper.c | 16 ----------------
> 2 files changed, 4 insertions(+), 20 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
> index d8b7099abece..a76000ee2a43 100644
> --- a/drivers/gpu/drm/drm_crtc.c
> +++ b/drivers/gpu/drm/drm_crtc.c
> @@ -2187,16 +2187,18 @@ 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 +2241,7 @@ 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.
> - */
I think there's still some value in the part of this comment that
explains why we're choosing not to call drm_mode_set_config_internal().
> - tmpfb = plane->fb;
> ret = crtc->funcs->set_config(&set);
> - plane->fb = tmpfb;
>
> kfree(connector_list);
> return ret;
> --
> 1.9.2
>
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--
Matt Roper
Graphics Software Engineer
IoTG Platform Enabling & Development
Intel Corporation
(916) 356-2795
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