From nobody Thu Dec 18 05:40:22 2025 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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 26259C61D99 for ; Wed, 22 Nov 2023 16:21:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235174AbjKVQVF (ORCPT ); Wed, 22 Nov 2023 11:21:05 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47296 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232644AbjKVQU6 (ORCPT ); Wed, 22 Nov 2023 11:20:58 -0500 Received: from fanzine2.igalia.com (fanzine.igalia.com [178.60.130.6]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id AAC481B8 for ; Wed, 22 Nov 2023 08:20:50 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=igalia.com; s=20170329; h=Content-Transfer-Encoding:Content-Type:MIME-Version:References: In-Reply-To:Message-ID:Date:Subject:Cc:To:From:Sender:Reply-To:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:List-Id:List-Help:List-Unsubscribe:List-Subscribe: List-Post:List-Owner:List-Archive; bh=LgiP6k4b25j6JdOl1t3vzbWpalkz+TaPG+lRilXJhV0=; b=QUMPjg4YQvQo+GWFK/4494HEuy rDbyp+KIU3owVzNlGUlll01Ecxk0G5hSpLUk1kYdO5RVPKm9qYBlnXSrnFJGx695NoaHrAG842lFe 5UyEqnz66VZR4ydlO49u3LFEtJcAbsLs7DS26s7fFoQavfPZkt8lEFzzjpiwYM0MnCU2QmzdprWZA ImjWX+UpkODk0aIWKOONuZ7SrGKK3p7CT2cNfkl3k4JcUg0BCBSheK67BExi7+rLI0/nZBYbq2pd7 CobE7liFqYjf7kfeVOPgGSJYWs25ygFn0Li48MqB3lL25Hb8SwWMT5g+nUt16DzaqafSSnKTxh09R kybx9Bcg==; Received: from 189-69-166-209.dial-up.telesp.net.br ([189.69.166.209] helo=steammachine.lan) by fanzine2.igalia.com with esmtpsa (Cipher TLS1.3:ECDHE_X25519__RSA_PSS_RSAE_SHA256__AES_256_GCM:256) (Exim) id 1r5py3-0061lT-FC; Wed, 22 Nov 2023 17:20:47 +0100 From: =?UTF-8?q?Andr=C3=A9=20Almeida?= To: dri-devel@lists.freedesktop.org, amd-gfx@lists.freedesktop.org, linux-kernel@vger.kernel.org Cc: kernel-dev@igalia.com, alexander.deucher@amd.com, christian.koenig@amd.com, pierre-eric.pelloux-prayer@amd.com, Simon Ser , Rob Clark , Pekka Paalanen , daniel@ffwll.ch, Daniel Stone , =?UTF-8?q?=27Marek=20Ol=C5=A1=C3=A1k=27?= , Dave Airlie , =?UTF-8?q?Michel=20D=C3=A4nzer?= , Randy Dunlap , ville.syrjala@linux.intel.com, intel-gfx@lists.freedesktop.org, Pekka Paalanen , =?UTF-8?q?Andr=C3=A9=20Almeida?= Subject: [PATCH v9 4/4] drm/doc: Define KMS atomic state set Date: Wed, 22 Nov 2023 13:19:41 -0300 Message-ID: <20231122161941.320564-5-andrealmeid@igalia.com> X-Mailer: git-send-email 2.42.1 In-Reply-To: <20231122161941.320564-1-andrealmeid@igalia.com> References: <20231122161941.320564-1-andrealmeid@igalia.com> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Pekka Paalanen Specify how the atomic state is maintained between userspace and kernel, plus the special case for async flips. Signed-off-by: Pekka Paalanen Signed-off-by: Andr=C3=A9 Almeida --- v9: - no changes v8: - no changes v7: - add a note that drivers can make exceptions for ad-hoc prop changes - add a note about flipping the same FB_ID as a no-op --- --- Documentation/gpu/drm-uapi.rst | 47 ++++++++++++++++++++++++++++++++++ 1 file changed, 47 insertions(+) diff --git a/Documentation/gpu/drm-uapi.rst b/Documentation/gpu/drm-uapi.rst index 370d820be248..d0693f902a5c 100644 --- a/Documentation/gpu/drm-uapi.rst +++ b/Documentation/gpu/drm-uapi.rst @@ -570,3 +570,50 @@ dma-buf interoperability =20 Please see Documentation/userspace-api/dma-buf-alloc-exchange.rst for information on how dma-buf is integrated and exposed within DRM. + +KMS atomic state +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D + +An atomic commit can change multiple KMS properties in an atomic fashion, +without ever applying intermediate or partial state changes. Either the w= hole +commit succeeds or fails, and it will never be applied partially. This is = the +fundamental improvement of the atomic API over the older non-atomic API wh= ich is +referred to as the "legacy API". Applying intermediate state could unexpe= ctedly +fail, cause visible glitches, or delay reaching the final state. + +An atomic commit can be flagged with DRM_MODE_ATOMIC_TEST_ONLY, which mean= s the +complete state change is validated but not applied. Userspace should use = this +flag to validate any state change before asking to apply it. If validation= fails +for any reason, userspace should attempt to fall back to another, perhaps +simpler, final state. This allows userspace to probe for various configur= ations +without causing visible glitches on screen and without the need to undo a +probing change. + +The changes recorded in an atomic commit apply on top the current KMS stat= e in +the kernel. Hence, the complete new KMS state is the complete old KMS stat= e with +the committed property settings done on top. The kernel will try to avoid +no-operation changes, so it is safe for userspace to send redundant proper= ty +settings. However, not every situation allows for no-op changes, due to t= he +need to acquire locks for some attributes. Userspace needs to be aware tha= t some +redundant information might result in oversynchronization issues. No-oper= ation +changes do not count towards actually needed changes, e.g. setting MODE_I= D to a +different blob with identical contents as the current KMS state shall not = be a +modeset on its own. As a special exception for VRR needs, explicitly setti= ng +FB_ID to its current value is not a no-op. + +A "modeset" is a change in KMS state that might enable, disable, or tempor= arily +disrupt the emitted video signal, possibly causing visible glitches on scr= een. A +modeset may also take considerably more time to complete than other kinds = of +changes, and the video sink might also need time to adapt to the new signal +properties. Therefore a modeset must be explicitly allowed with the flag +DRM_MODE_ATOMIC_ALLOW_MODESET. This in combination with +DRM_MODE_ATOMIC_TEST_ONLY allows userspace to determine if a state change = is +likely to cause visible disruption on screen and avoid such changes when e= nd +users do not expect them. + +An atomic commit with the flag DRM_MODE_PAGE_FLIP_ASYNC is allowed to +effectively change only the FB_ID property on any planes. No-operation cha= nges +are ignored as always. Changing any other property will cause the commit t= o be +rejected. Each driver may relax this restriction if they have guarantees t= hat +such property change doesn't cause modesets. Userspace can use TEST_ONLY c= ommits +to query the driver about this. --=20 2.42.1