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Fri, 22 May 2026 11:56:00 +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 pnoOK1BEEGohWAAAD6G6ig (envelope-from ); Fri, 22 May 2026 11:56:00 +0000 Message-ID: Date: Fri, 22 May 2026 13:55:59 +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] drm/client: check whether CRTC is active before waiting for vblank To: Icenowy Zheng , Maarten Lankhorst , Maxime Ripard , David Airlie , Simona Vetter , Sam Ravnborg Cc: dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, Icenowy Zheng , stable@vger.kernel.org References: <20260519092420.1124348-1-zhengxingda@iscas.ac.cn> Content-Language: en-US From: Thomas Zimmermann Autocrypt: addr=tzimmermann@suse.de; keydata= xsBNBFs50uABCADEHPidWt974CaxBVbrIBwqcq/WURinJ3+2WlIrKWspiP83vfZKaXhFYsdg XH47fDVbPPj+d6tQrw5lPQCyqjwrCPYnq3WlIBnGPJ4/jreTL6V+qfKRDlGLWFjZcsrPJGE0 BeB5BbqP5erN1qylK9i3gPoQjXGhpBpQYwRrEyQyjuvk+Ev0K1Jc5tVDeJAuau3TGNgah4Yc hdHm3bkPjz9EErV85RwvImQ1dptvx6s7xzwXTgGAsaYZsL8WCwDaTuqFa1d1jjlaxg6+tZsB 9GluwvIhSezPgnEmimZDkGnZRRSFiGP8yjqTjjWuf0bSj5rUnTGiyLyRZRNGcXmu6hjlABEB AAHNJ1Rob21hcyBaaW1tZXJtYW5uIDx0emltbWVybWFubkBzdXNlLmRlPsLAjgQTAQgAOAIb AwULCQgHAgYVCgkICwIEFgIDAQIeAQIXgBYhBHIX+6yM6c9jRKFo5WgNwR1TC3ojBQJftODH AAoJEGgNwR1TC3ojx1wH/0hKGWugiqDgLNXLRD/4TfHBEKmxIrmfu9Z5t7vwUKfwhFL6hqvo lXPJJKQpQ2z8+X2vZm/slsLn7J1yjrOsoJhKABDi+3QWWSGkaGwRJAdPVVyJMfJRNNNIKwVb U6B1BkX2XDKDGffF4TxlOpSQzdtNI/9gleOoUA8+jy8knnDYzjBNOZqLG2FuTdicBXblz0Mf vg41gd9kCwYXDnD91rJU8tzylXv03E75NCaTxTM+FBXPmsAVYQ4GYhhgFt8S2UWMoaaABLDe 7l5FdnLdDEcbmd8uLU2CaG4W2cLrUaI4jz2XbkcPQkqTQ3EB67hYkjiEE6Zy3ggOitiQGcqp j//OwE0EWznS4AEIAMYmP4M/V+T5RY5at/g7rUdNsLhWv1APYrh9RQefODYHrNRHUE9eosYb T6XMryR9hT8XlGOYRwKWwiQBoWSDiTMo/Xi29jUnn4BXfI2px2DTXwc22LKtLAgTRjP+qbU6 3Y0xnQN29UGDbYgyyK51DW3H0If2a3JNsheAAK+Xc9baj0LGIc8T9uiEWHBnCH+RdhgATnWW GKdDegUR5BkDfDg5O/FISymJBHx2Dyoklv5g4BzkgqTqwmaYzsl8UxZKvbaxq0zbehDda8lv hFXodNFMAgTLJlLuDYOGLK2AwbrS3Sp0AEbkpdJBb44qVlGm5bApZouHeJ/+n+7r12+lqdsA EQEAAcLAdgQYAQgAIAIbDBYhBHIX+6yM6c9jRKFo5WgNwR1TC3ojBQJftOH6AAoJEGgNwR1T C3ojVSkIALpAPkIJPQoURPb1VWjh34l0HlglmYHvZszJWTXYwavHR8+k6Baa6H7ufXNQtThR yIxJrQLW6rV5lm7TjhffEhxVCn37+cg0zZ3j7zIsSS0rx/aMwi6VhFJA5hfn3T0TtrijKP4A SAQO9xD1Zk9/61JWk8OysuIh7MXkl0fxbRKWE93XeQBhIJHQfnc+YBLprdnxR446Sh8Wn/2D Ya8cavuWf2zrB6cZurs048xe0UbSW5AOSo4V9M0jzYI4nZqTmPxYyXbm30Kvmz0rYVRaitYJ 4kyYYMhuULvrJDMjZRvaNe52tkKAvMevcGdt38H4KSVXAylqyQOW5zvPc4/sq9c= In-Reply-To: <20260519092420.1124348-1-zhengxingda@iscas.ac.cn> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit 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)[-0.999]; MIME_GOOD(-0.10)[text/plain]; RCVD_VIA_SMTP_AUTH(0.00)[]; FREEMAIL_TO(0.00)[iscas.ac.cn,linux.intel.com,kernel.org,gmail.com,ffwll.ch,ravnborg.org]; ARC_NA(0.00)[]; MIME_TRACE(0.00)[0:+]; RCPT_COUNT_SEVEN(0.00)[10]; FUZZY_RATELIMITED(0.00)[rspamd.com]; 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]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:helo,suse.de:mid,suse.com:url,iscas.ac.cn:email] X-Spam-Level: X-Spam-Flag: NO Hi Am 19.05.26 um 11:24 schrieb Icenowy Zheng: > Currently the implementaion of drm_client_modeset_wait_for_vblank() > assumes drm_vblank_get() will fail when the CRTC isn't active. However > it seems that this is not true, and running fbcon on a device with the > first CRTC inactive will lead to kernel warning in some cases (which > could be reproduced with the loongson driver). > > Change the implementation to add a check for the active state (atomic) / > enabled state (non-atomic) before calling drm_vblank_get(). As the > assumption of drm_vblank_get() failing for inactive CRTC isn't met, the > error status of drm_vblank_get() can now be exported too. > > Cc: stable@vger.kernel.org > Fixes: d8c4bddcd8bc ("drm/fb-helper: Synchronize dirty worker with vblank") > Signed-off-by: Icenowy Zheng > --- > drivers/gpu/drm/drm_client_modeset.c | 13 +++++++++++-- > 1 file changed, 11 insertions(+), 2 deletions(-) > > diff --git a/drivers/gpu/drm/drm_client_modeset.c b/drivers/gpu/drm/drm_client_modeset.c > index bb49b8361271a..1b03bf351256e 100644 > --- a/drivers/gpu/drm/drm_client_modeset.c > +++ b/drivers/gpu/drm/drm_client_modeset.c > @@ -1310,7 +1310,7 @@ int drm_client_modeset_wait_for_vblank(struct drm_client_dev *client, unsigned i > { > struct drm_device *dev = client->dev; > struct drm_crtc *crtc; > - int ret; > + int ret = 0; > > /* > * Rate-limit update frequency to vblank. If there's a DRM master > @@ -1326,15 +1326,24 @@ int drm_client_modeset_wait_for_vblank(struct drm_client_dev *client, unsigned i > * Only wait for a vblank event if the CRTC is enabled, otherwise > * just don't do anything, not even report an error. > */ > + if (drm_drv_uses_atomic_modeset(dev)) { > + if (!crtc->state || !crtc->state->active) > + goto out; > + } else { > + if (!crtc->enabled) > + goto out; > + } > + This part is good. > ret = drm_crtc_vblank_get(crtc); > if (!ret) { > drm_crtc_wait_one_vblank(crtc); > drm_crtc_vblank_put(crtc); > } > > +out: > drm_master_internal_release(dev); > > - return 0; > + return ret; But this isn't. There can be CRTCs without any vblank at all. We still want to fail silently for them. So we still have to return 0 here. Having set this, fixing this helper is only partially what you want. Since your device has vblanking, the emulation should check on the correct CRTC. IOW you need to pass the right CRTC index at https://elixir.bootlin.com/linux/v7.1-rc1/source/drivers/gpu/drm/drm_fb_helper.c#L237 https://elixir.bootlin.com/linux/v7.1-rc1/source/drivers/gpu/drm/drm_fb_helper.c#L920 I'm not quite sure how to support this. The CRTC is under fb_helper->client.modesets.crtc. You'd have to figure out which is the relevant one and use that. But that's also not so great, as fbdev ioctls only support CRTC 0. Doing internal re-mappings only complicates matters. But why does your HW use CRTC 1 in the first place. Best regards Thomas > } > EXPORT_SYMBOL(drm_client_modeset_wait_for_vblank); > -- -- 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)