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Mon, 22 Jun 2026 14:54:36 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id DRWPAqxMOWrdeQAAD6G6ig (envelope-from ); Mon, 22 Jun 2026 14:54:36 +0000 Message-ID: <926d9d5f-be68-4377-9a90-0d9ace2c2c53@suse.de> Date: Mon, 22 Jun 2026 16:54:35 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] drm/fb-helper: Only consider active CRTCs for vblank sync To: Jani Nikula , hns@goldelico.com, zhengxingda@iscas.ac.cn, maarten.lankhorst@linux.intel.com, mripard@kernel.org, airlied@gmail.com, simona@ffwll.ch, akemnade@kernel.org Cc: dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, letux-kernel@openphoenux.org, kernel@pyra-handheld.com, sashiko-reviews@lists.linux.dev, stable@vger.kernel.org References: <20260622113434.682292-1-tzimmermann@suse.de> <395f15bb770b4be0ffeeb09e7cdeef49340f910c@intel.com> Content-Language: en-US From: Thomas Zimmermann Autocrypt: addr=tzimmermann@suse.de; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Spam-Flag: NO X-Spam-Score: -4.30 X-Spamd-Result: default: False [-4.30 / 50.00]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-0.993]; MIME_GOOD(-0.10)[text/plain]; ARC_NA(0.00)[]; RCPT_COUNT_TWELVE(0.00)[14]; MIME_TRACE(0.00)[0:+]; FUZZY_RATELIMITED(0.00)[rspamd.com]; FREEMAIL_TO(0.00)[linux.intel.com,goldelico.com,iscas.ac.cn,kernel.org,gmail.com,ffwll.ch]; RCVD_VIA_SMTP_AUTH(0.00)[]; MID_RHS_MATCH_FROM(0.00)[]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; RCVD_TLS_ALL(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; URIBL_BLOCKED(0.00)[iscas.ac.cn:email,suse.com:url,suse.de:email,suse.de:mid,imap1.dmz-prg2.suse.org:helo,goldelico.com:email]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.com:url,iscas.ac.cn:email,suse.de:email,suse.de:mid,imap1.dmz-prg2.suse.org:helo] X-Spam-Level: Hi Am 22.06.26 um 15:34 schrieb Jani Nikula: > On Mon, 22 Jun 2026, Thomas Zimmermann wrote: >> Only synchronize fbdev output to the vblank of an active CRTC. Go over >> the list of CRTCs and pick the first that matches. Fixes warnings as >> the one shown below >> >> [ 77.201354] WARNING: drivers/gpu/drm/drm_vblank.c:1320 at drm_crtc_wait_one_vblank+0x194/0x1cc [drm], CPU#1: kworker/1:7/1867 >> [ 77.201354] omapdrm omapdrm.0: [drm] vblank wait timed out on crtc 0 >> >> This currently happens if the fbdev output is not on CRTC 0. >> >> Atomic and non-atomic drivers require distinct code paths. As for other >> fbdev operations, implement both and select the correct one at runtime. >> >> Not finding an active CRTC is not a bug. Do not wait in this case, but >> flush the display update as before. >> >> v2: >> - move look-up code into separate helper >> - support drivers with legacy modesetting >> v1: >> - see https://lore.kernel.org/dri-devel/1c9e0e24-9c4a-4259-8700-cf9e5fd60ca3@suse.de/ >> >> Co-authored-by: H. Nikolaus Schaller >> Signed-off-by: Thomas Zimmermann >> Fixes: d8c4bddcd8bcb ("drm/fb-helper: Synchronize dirty worker with vblank") >> Tested-by: Icenowy Zheng >> Closes: https://bugs.debian.org/1138033 >> Cc: # v6.19+ >> --- >> drivers/gpu/drm/drm_fb_helper.c | 71 ++++++++++++++++++++++++++++++++- >> 1 file changed, 70 insertions(+), 1 deletion(-) >> >> diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c >> index 7b11a582f8ec..cbf0a9a7b8e5 100644 >> --- a/drivers/gpu/drm/drm_fb_helper.c >> +++ b/drivers/gpu/drm/drm_fb_helper.c >> @@ -225,16 +225,85 @@ static void drm_fb_helper_resume_worker(struct work_struct *work) >> console_unlock(); >> } >> >> +static int find_crtc_index_atomic(struct drm_fb_helper *helper) >> +{ >> + struct drm_device *dev = helper->dev; >> + struct drm_plane *plane; >> + >> + drm_for_each_plane(plane, dev) { >> + const struct drm_plane_state *plane_state; >> + const struct drm_crtc *crtc; >> + >> + if (plane->type != DRM_PLANE_TYPE_PRIMARY) >> + continue; >> + >> + plane_state = plane->state; >> + if (plane_state->fb != helper->fb || !plane_state->crtc) >> + continue; /* plane doesn't display fbdev emulation */ >> + >> + crtc = plane_state->crtc; >> + if (!crtc->state->active) >> + continue; >> + if (drm_WARN_ON_ONCE(dev, crtc->index > INT_MAX)) >> + continue; /* driver bug */ > I take it this is here because crtc->index is unsigned, and this > function returns int so you can have negative error codes. Ditto the > other function below. > > I feel like this is something that should be checked once somewhere, if > that. I think adding arbitrary checks like this invites more arbitrary > checks everywhere. crtc->index is supposed to be invariant over the > lifetime of the CRTC. Ok, makes sense. Best regards Thomas > > BR, > Jani. > >> + >> + return crtc->index; >> + } >> + >> + return -EINVAL; >> +} >> + >> +static int find_crtc_index_legacy(struct drm_fb_helper *helper) >> +{ >> + struct drm_device *dev = helper->dev; >> + struct drm_crtc *crtc; >> + >> + drm_for_each_crtc(crtc, dev) { >> + struct drm_plane *plane = crtc->primary; >> + >> + if (!crtc->enabled) >> + continue; >> + if (!plane || plane->fb != helper->fb) >> + continue; /* CRTC doesn't display fbdev emulation */ >> + if (drm_WARN_ON_ONCE(dev, crtc->index > INT_MAX)) >> + continue; /* driver bug */ >> + >> + return crtc->index; >> + } >> + >> + return -EINVAL; >> +} >> + >> +static int drm_fb_helper_find_crtc_index(struct drm_fb_helper *helper) >> +{ >> + struct drm_device *dev = helper->dev; >> + int crtc_index; >> + >> + mutex_lock(&dev->mode_config.mutex); >> + >> + if (drm_drv_uses_atomic_modeset(dev)) >> + crtc_index = find_crtc_index_atomic(helper); >> + else >> + crtc_index = find_crtc_index_legacy(helper); >> + >> + mutex_unlock(&dev->mode_config.mutex); >> + >> + return crtc_index; >> +} >> + >> static void drm_fb_helper_fb_dirty(struct drm_fb_helper *helper) >> { >> struct drm_device *dev = helper->dev; >> struct drm_clip_rect *clip = &helper->damage_clip; >> struct drm_clip_rect clip_copy; >> + int crtc_index; >> unsigned long flags; >> int ret; >> >> mutex_lock(&helper->lock); >> - drm_client_modeset_wait_for_vblank(&helper->client, 0); >> + crtc_index = drm_fb_helper_find_crtc_index(helper); >> + if (crtc_index >= 0) >> + drm_client_modeset_wait_for_vblank(&helper->client, crtc_index); >> mutex_unlock(&helper->lock); >> >> if (drm_WARN_ON_ONCE(dev, !helper->funcs->fb_dirty)) -- -- Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Frankenstr. 146, 90461 Nürnberg, Germany, www.suse.com GF: Jochen Jaser, Andrew McDonald, Werner Knoblich, (HRB 36809, AG Nürnberg)