From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 1AA1FC982FA for ; Tue, 22 Sep 2026 12:09:05 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id A42E910EC88; Tue, 22 Sep 2026 12:09:04 +0000 (UTC) Authentication-Results: gabe.freedesktop.org; dkim=pass (1024-bit key; unprotected) header.d=suse.de header.i=@suse.de header.b="X920EZ83"; dkim=permerror (0-bit key) header.d=suse.de header.i=@suse.de header.b="ZvlFX0Jr"; dkim=pass (1024-bit key) header.d=suse.de header.i=@suse.de header.b="vzXWCjGe"; dkim=permerror (0-bit key) header.d=suse.de header.i=@suse.de header.b="Sq9bK5VC"; dkim-atps=neutral Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.223.130]) by gabe.freedesktop.org (Postfix) with ESMTPS id 7382110EC85; Tue, 22 Sep 2026 12:09:02 +0000 (UTC) Received: from imap1.dmz-prg2.suse.org (unknown [10.150.64.97]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by smtp-out1.suse.de (Postfix) with ESMTPS id A396121AA9; Tue, 22 Sep 2026 12:08:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1790078930; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:autocrypt:autocrypt; bh=rLRc8zl8aqIxSR1VL/Mye3FkV1bGaBSyopMMs4u2HOE=; b=X920EZ83Fd0OKixtr/YnbBwrTBiE+9Im6QA4ji7vnX7qJii1sCf9knSAq1lHbOquttejTs BDBvRd2I9j3PF4+hGW0ln9i6IvwuioUCYAcuC7Nhe60frkq54/S9Iwqf2C3tHcRRB44huI EW8/wKeNUt3Yrq1By3j7CfkZPXXHd0M= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1790078930; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:autocrypt:autocrypt; bh=rLRc8zl8aqIxSR1VL/Mye3FkV1bGaBSyopMMs4u2HOE=; b=ZvlFX0JruSP2fMYR8Nv4PoRXy9BDQbo2JAm9KV8bLpsVOcFkAG87sY5VbeTr7BPmHRzsWE aSnosGmvXlb59aCQ== Authentication-Results: smtp-out1.suse.de; none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1790078926; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:autocrypt:autocrypt; bh=rLRc8zl8aqIxSR1VL/Mye3FkV1bGaBSyopMMs4u2HOE=; b=vzXWCjGegunU2ndkjp+KSguebUpNlXX1IXO2ZdoiyFsCnNmbGPm30TY4UsDvEUVoU7grTQ l6T4GrVMjimYdCsCiTWQ21QkHaCd4CRK+4DJbUyzkwh1hImgeKXQNW8tLW0Rt/EehrAouh NZzriGK9nUX6xkbk3OfvGqTlmdMj67s= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1790078926; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:autocrypt:autocrypt; bh=rLRc8zl8aqIxSR1VL/Mye3FkV1bGaBSyopMMs4u2HOE=; b=Sq9bK5VCZ719j8QiitEP/6aQ8cfNdnrOkXKBoOSw8Rs2BZoLJ+Nw3STraBJUFx7yS0O885 hgZBqHLwklzm3/Cg== Received: from imap1.dmz-prg2.suse.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by imap1.dmz-prg2.suse.org (Postfix) with ESMTPS id B8F01132D3; Tue, 22 Sep 2026 12:08:45 +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 0CYOHM1vsmr5GwAAD6G6ig (envelope-from ); Tue, 22 Sep 2026 12:08:45 +0000 Message-ID: Date: Tue, 22 Sep 2026 14:08:45 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v8 04/14] drm: add connector backlight (LUMINANCE) infrastructure To: Javier Martinez Canillas , Mario Limonciello , dri-devel@lists.freedesktop.org, harry.wentland@amd.com, Simona Vetter , Alex Deucher , Maarten Lankhorst , Maxime Ripard , David Airlie Cc: Xaver Hugl , amd-gfx@lists.freedesktop.org, "open list:INTEL DRM DISPLAY FOR XE AND I915 DRIVERS" , "open list:INTEL DRM DISPLAY FOR XE AND I915 DRIVERS" , Hans de Goede , David Herrmann , Mario Limonciello References: <20260908044035.62093-1-mario.limonciello@amd.com> <20260908044035.62093-5-mario.limonciello@amd.com> 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: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Spamd-Result: default: False [-2.80 / 50.00]; BAYES_HAM(-3.00)[100.00%]; SUSPICIOUS_RECIPS(1.50)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; TAGGED_RCPT(0.00)[]; RCVD_TLS_ALL(0.00)[]; MIME_TRACE(0.00)[0:+]; RCPT_COUNT_TWELVE(0.00)[16]; RCVD_VIA_SMTP_AUTH(0.00)[]; ARC_NA(0.00)[]; FREEMAIL_TO(0.00)[redhat.com,amd.com,lists.freedesktop.org,ffwll.ch,linux.intel.com,kernel.org,gmail.com]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; TO_DN_SOME(0.00)[]; FROM_HAS_DN(0.00)[]; FREEMAIL_CC(0.00)[gmail.com,lists.freedesktop.org,kernel.org]; MID_RHS_MATCH_FROM(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:helo, suse.com:url, suse.de:mid] X-BeenThere: intel-gfx@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Intel graphics driver community testing & development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" Hi Am 22.09.26 um 13:42 schrieb Javier Martinez Canillas: > Mario Limonciello writes: > >> Backlight brightness is a property of a display, and thus of a DRM >> connector, yet it has historically only been controllable through the >> separate backlight sysfs interface. Add a generic, backend-agnostic >> per-connector LUMINANCE range property so brightness can be driven >> through the atomic modeset path like any other connector state. >> >> A struct drm_backlight is embedded in every connector and initialized by >> the core; drivers do not allocate it. A driver links a backend (today a >> backlight_device, in the future DDC/CI, MIPI-DCS, ...) with >> drm_backlight_link(), which creates the connector's LUMINANCE property > The infrastructure is meant to be backend-agnostic but drm_backlight_link() > which creates the connector's LUMINANCE property is backend specific. Maybe > would be better to not call drm_backlight to the DRM core helpers since it > conflates the backlight subsystem specific helpers, and the ones that are > supposed to be backend-agnostic. > > Maybe drm_brightness or drm_luminance would be more suitable? That way would > be clear what is generic infra to handle the LUMINANCE property and what is > specific to drivers using a backlight device. > > In fact, I think that would be better if you split this patch in the DRM core > helpers and another patch that adds the backlight specific helpers on top. It > would also be useful to have an example of a "native" backend, for drivers that > have a trivial brightness management. > > For example, many small I2C or SPI display panels just send a few commands over > the bus to change the backlight brightness. Those may have their own get/set > luminance callbacks and register their own struct drm_backlight_funcs. > > Because right now seems to me that this drm_backlight infrastructure is mixing > the two layers and we have a leaky abstraction. > >> with the backend's range. The property value is staged into the atomic >> connector state and only pushed to the hardware from the commit/enable >> path, via a workqueue so that slow backends never stall a commit. DPMS >> off drives the backlight to 0 and DPMS on restores the committed value. >> >> The property range is per-connector (created from the backend's >> max_brightness), so multiple panels no longer share and corrupt a single >> device-wide range. drm_backlight_link() also carries the legacy-sysfs >> takeover accounting used by the client capability added in a later patch. >> >> The whole feature is guarded by CONFIG_DRM_BACKLIGHT (which depends on, >> rather than selects, BACKLIGHT_CLASS_DEVICE) so DRM does not pull the >> backlight subsystem into the kernel when it is not wanted. >> > If we had a good separation between the drm_backlight core helpers and the > backlight subsystem then this dependency wouldn't be needed. Drivers would > use depend on CONFIG_DRM_BACKLIGHT to use the drm_backlight helpers and use > BACKLIGHT_CLASS_DEVICE dependent helpers, to be used as set/get callbacks. > > Since DRM drivers that register a backlight device already depend on this > Kconfig symbol, no additional dependencies will be needed. And drivers that > only use the CONFIG_DRM_BACKLIGHT (with a different backend), won't need to > depend on CONFIG_DRM_BACKLIGHT. > > In general, I think is preferable to have good helper functions that could > be reused by drivers, instead of having mid-layers such as drm_backlight_link(). I want to second what Javier says here. I raise the same points in my rant about DRM design. Best regards Thomas > -- -- Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Frankenstr. 146, 90461 Nürnberg, Germany, www.suse.com GF: Jochen Jaser, Andrew McDonald, (HRB 36809, AG Nürnberg)