From mboxrd@z Thu Jan 1 00:00:00 1970 From: Matt Roper Subject: Re: [PATCH] drm: Simplify fb refcounting rules around ->update_plane Date: Tue, 22 Apr 2014 18:08:58 -0700 Message-ID: <20140423010858.GT1063@intel.com> References: <20140422100622.GU18465@intel.com> <1398176385-32174-1-git-send-email-daniel.vetter@ffwll.ch> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Return-path: Received: from mga03.intel.com (mga03.intel.com [143.182.124.21]) by gabe.freedesktop.org (Postfix) with ESMTP id 91B126E986 for ; Tue, 22 Apr 2014 18:06:02 -0700 (PDT) Content-Disposition: inline In-Reply-To: <1398176385-32174-1-git-send-email-daniel.vetter@ffwll.ch> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" To: Daniel Vetter Cc: Thierry Reding , DRI Development List-Id: dri-devel@lists.freedesktop.org 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=3D0. 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 > Cc: Ville Syrj=E4l=E4 > Signed-off-by: Daniel Vetter > --- > 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, voi= d *data, > } > = > drm_modeset_lock_all(dev); > + old_fb =3D plane->fb; > ret =3D 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 =3D plane->fb; > plane->crtc =3D crtc; > plane->fb =3D fb; > fb =3D NULL; > + } else { > + old_fb =3D NULL; > } > drm_modeset_unlock_all(dev); > = > @@ -2239,9 +2241,7 @@ int drm_mode_set_config_internal(struct drm_mode_se= t *set) > ret =3D crtc->funcs->set_config(set); > if (ret =3D=3D 0) { > crtc->primary->crtc =3D crtc; > - > - /* crtc->fb must be updated by ->set_config, enforces this. */ > - WARN_ON(fb !=3D crtc->primary->fb); > + crtc->primary->fb =3D 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_pla= ne_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 =3D 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 *plan= e, struct drm_crtc *crtc, > set.connectors =3D connector_list; > set.num_connectors =3D 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 =3D plane->fb; > ret =3D crtc->funcs->set_config(&set); > - plane->fb =3D tmpfb; > = > kfree(connector_list); > return ret; > -- = > 1.9.2 > = > _______________________________________________ > dri-devel mailing list > dri-devel@lists.freedesktop.org > http://lists.freedesktop.org/mailman/listinfo/dri-devel -- = Matt Roper Graphics Software Engineer IoTG Platform Enabling & Development Intel Corporation (916) 356-2795