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Wed, 18 Mar 2026 07:09:26 +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 bjXsJqZPummxHAAAD6G6ig (envelope-from ); Wed, 18 Mar 2026 07:09:26 +0000 Message-ID: <27689c69-dca3-4d5b-b385-b9ee2391a9d9@suse.de> Date: Wed, 18 Mar 2026 08:09:26 +0100 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/loongson: stop to set get_vblank_timestamp for 7A1000 CRTC To: Icenowy Zheng , Sui Jingfeng , Maarten Lankhorst , Maxime Ripard , David Airlie , Simona Vetter Cc: dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org References: <20260314165421.1201790-1-zhengxingda@iscas.ac.cn> <8b52a9190a237a8bb94a23bf06b6a0589394f553.camel@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: <8b52a9190a237a8bb94a23bf06b6a0589394f553.camel@iscas.ac.cn> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Spam-Score: -4.30 X-Spam-Level: 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)[-1.000]; MIME_GOOD(-0.10)[text/plain]; RCVD_VIA_SMTP_AUTH(0.00)[]; FREEMAIL_TO(0.00)[iscas.ac.cn,loongson.cn,linux.intel.com,kernel.org,gmail.com,ffwll.ch]; ARC_NA(0.00)[]; MIME_TRACE(0.00)[0:+]; RCPT_COUNT_SEVEN(0.00)[8]; 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.de:email,suse.com:url] X-Spam-Flag: NO Hi Am 18.03.26 um 07:16 schrieb Icenowy Zheng: > 在 2026-03-16一的 08:53 +0100，Thomas Zimmermann写道： >> >> Am 14.03.26 um 17:54 schrieb Icenowy Zheng: >>> As there's no known hardware capability about querying vblank on >>> the >>> 7A1000 display controller, setting get_vblank_timestamp will >>> mislead the >>> kernel about the support of DC-backed high precision vblank query. >>> >>> Drop this function pointer in the CRTC function table for 7A1000. >>> >>> This solves a kernel warning when booting Linux 7.0-rc3 on a >>> 3A4000+7A1000 Haier Boyue G51 laptop (with injected EDID for >>> replicating >>> the display timing set by the firmware). >>> >>> Signed-off-by: Icenowy Zheng >> Acked-by: Thomas Zimmermann > Well, is my following understand right? > > - A hardware that does not have hardware vblank timing/counting ability > shouldn't set .get_vblank_timestamp . > - A hardware that supports vblank counting but not timing should set > .get_vblank_timestamp to the > drm_crtc_vblank_helper_get_vblank_timestamp helper to allow vblank > timing estimate with counter. Setting drm_crtc_vblank_helper_get_vblank_timestamp() also requires to read out the x/y positions. See get_scanout_position. You can leave out get_vblank_timestamp entirely and DRM will approximate the values with the system timer. For reading the vblank counter, there's get_vblank_counter if the hardware supports it. > > (P.S. There's a DisplayCurrentLocation register that is valid for > 7A1000, which returns the current X and Y positions; but I wonder > whether this is meaningful for vblank querying. That sounds like the functionality required for get_scanout_position. > In addition, this DC looks quite similar to Verisilicon DCNano, which > was used by i.MX8ULP (although many functionality on the i.MX8ULP > manual is missing, things until cursor0 match between LS7A2000 manual > and i.MX8ULP manual). I wonder whether NXP people abandoned the > mainlining of DCNano driver because of drm/loongson?) IDK anything about that. > P.S.2. I saw that Sui Jingfeng's mailbox is bouncing and the driver is > going to be orphaned. If he wouldn't react with other ways, maybe I > could try to maintain this driver? I have Loongson-3A4000 + LS7A1000 > and Loongson-3A6000 + LS7A2000 hardwares at home. Yes, the driver is now orphaned.  No one else from Loongson has shown up to maintain it either. If you want it, just send a patch to add you as maintainer with a short rational. Best regards Thomas > >>> --- >>>   drivers/gpu/drm/loongson/lsdc_crtc.c | 1 - >>>   1 file changed, 1 deletion(-) >>> >>> diff --git a/drivers/gpu/drm/loongson/lsdc_crtc.c >>> b/drivers/gpu/drm/loongson/lsdc_crtc.c >>> index 587fbe285e9ef..b3af8e0cdb15f 100644 >>> --- a/drivers/gpu/drm/loongson/lsdc_crtc.c >>> +++ b/drivers/gpu/drm/loongson/lsdc_crtc.c >>> @@ -721,7 +721,6 @@ static const struct drm_crtc_funcs >>> ls7a1000_crtc_funcs = { >>>    .late_register = lsdc_crtc_late_register, >>>    .enable_vblank = lsdc_crtc_enable_vblank, >>>    .disable_vblank = lsdc_crtc_disable_vblank, >>> - .get_vblank_timestamp = >>> drm_crtc_vblank_helper_get_vblank_timestamp, >>>    .atomic_print_state = lsdc_crtc_atomic_print_state, >>>   }; >>> -- -- 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)