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Commit 0fe27f06 authored by Daniel Vetter's avatar Daniel Vetter
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drm: Simplify fb refcounting rules around ->update_plane 



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.

v5: Keep still useful comments about directly calling ->set_config,
which I should have done for v4 already. Requested by Matt.

Cc: Thierry Reding <treding@nvidia.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: default avatarMatt Roper <matthew.d.roper@intel.com>
Signed-off-by: default avatarDaniel Vetter <daniel.vetter@ffwll.ch>
parent 49d9ec1c

drivers/gpu/drm/drm_crtc.c

+7 −6
Original line number Diff line number Diff line
@@ -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) {

drivers/gpu/drm/drm_plane_helper.c

+1 −9
Original line number Diff line number Diff line
@@ -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) {
@@ -178,21 +177,14 @@ int drm_primary_helper_update(struct drm_plane *plane, struct drm_crtc *crtc, 
	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

	 * 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;