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 39CAFCDB474 for ; Tue, 17 Oct 2023 09:29:17 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 4E5E910E2A6; Tue, 17 Oct 2023 09:29:03 +0000 (UTC) Received: from fanzine2.igalia.com (fanzine.igalia.com [178.60.130.6]) by gabe.freedesktop.org (Postfix) with ESMTPS id E1C2A10E29A; Tue, 17 Oct 2023 09:28:52 +0000 (UTC) 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=Bv4UhAyma+StQ1C/srhttolaGUlSYmJrKK1FzAxXGo0=; b=bGnrI2i74XpILAOrXy08pbTd/v 81bMUL3IdoVDj6Bn0dsuwq+GforHlb+xY+LF8RrY2foCmwoMgFc+t7Oyp6z6N4sl6/nJ1aCYM1nqN 2ThxwX1I3zFVoBjU0mVJmu5Uljc14aHgdAWSITF+8T+9JvaNaEzdFL57sJJvSRU8RaFU+FIJwb5ZA DQ6S3DVsYafkafX3WrYvKpbdWdIVnptDnsugR+LKHn8lFfyEWTQYLT9LyKnO3aqdjEH/DXciYBOU9 Fgsg6X8+nHnDw+QuEMeYxc9Uxi8/7FRH2U2876fRjVxjZNXDlEw67P3Y+ZPuWhNbAu/fWs+sr/Ppe Qt8syUsw==; Received: from 167.red-81-39-185.dynamicip.rima-tde.net ([81.39.185.167] helo=localhost.localdomain) by fanzine2.igalia.com with esmtpsa (Cipher TLS1.3:ECDHE_X25519__RSA_PSS_RSAE_SHA256__AES_256_GCM:256) (Exim) id 1qsgNe-001ODF-Lc; Tue, 17 Oct 2023 11:28:50 +0200 From: =?UTF-8?q?Andr=C3=A9=20Almeida?= To: dri-devel@lists.freedesktop.org, amd-gfx@lists.freedesktop.org, linux-kernel@vger.kernel.org Subject: [PATCH v7 5/6] drm/doc: Define KMS atomic state set Date: Tue, 17 Oct 2023 11:28:36 +0200 Message-ID: <20231017092837.32428-6-andrealmeid@igalia.com> X-Mailer: git-send-email 2.42.0 In-Reply-To: <20231017092837.32428-1-andrealmeid@igalia.com> References: <20231017092837.32428-1-andrealmeid@igalia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: pierre-eric.pelloux-prayer@amd.com, Pekka Paalanen , =?UTF-8?q?=27Marek=20Ol=C5=A1=C3=A1k=27?= , =?UTF-8?q?Michel=20D=C3=A4nzer?= , Randy Dunlap , Pekka Paalanen , kernel-dev@igalia.com, alexander.deucher@amd.com, =?UTF-8?q?Andr=C3=A9=20Almeida?= , hwentlan@amd.com, christian.koenig@amd.com, joshua@froggi.es Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" 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: André Almeida --- 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 632989df3727..34bd02270ee7 100644 --- a/Documentation/gpu/drm-uapi.rst +++ b/Documentation/gpu/drm-uapi.rst @@ -570,3 +570,50 @@ dma-buf interoperability 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 +================ + +An atomic commit can change multiple KMS properties in an atomic fashion, +without ever applying intermediate or partial state changes. Either the whole +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 which is +referred to as the "legacy API". Applying intermediate state could unexpectedly +fail, cause visible glitches, or delay reaching the final state. + +An atomic commit can be flagged with DRM_MODE_ATOMIC_TEST_ONLY, which means 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 configurations +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 state in +the kernel. Hence, the complete new KMS state is the complete old KMS state 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 property +settings. However, not every situation allows for no-op changes, due to the +need to acquire locks for some attributes. Userspace needs to be aware that some +redundant information might result in oversynchronization issues. No-operation +changes do not count towards actually needed changes, e.g. setting MODE_ID 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 setting +FB_ID to its current value is not a no-op. + +A "modeset" is a change in KMS state that might enable, disable, or temporarily +disrupt the emitted video signal, possibly causing visible glitches on screen. 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 end +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 changes +are ignored as always. Changing any other property will cause the commit to be +rejected. Each driver may relax this restriction if they have guarantees that +such property change doesn't cause modesets. Userspace can use TEST_ONLY commits +to query the driver about this. -- 2.42.0