From patchwork Fri Jul 7 22:40:59 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: =?utf-8?q?Andr=C3=A9_Almeida?= X-Patchwork-Id: 13305396 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 0D5D3C001E0 for ; Fri, 7 Jul 2023 22:41:55 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id D426E10E613; Fri, 7 Jul 2023 22:41:45 +0000 (UTC) Received: from fanzine2.igalia.com (fanzine2.igalia.com [213.97.179.56]) by gabe.freedesktop.org (Postfix) with ESMTPS id D993E10E60F; Fri, 7 Jul 2023 22:41:44 +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=ILhK3ntOSguFvvoL3dtIQ/0orxl4TRRaxUfEny2T4hQ=; b=luAS5a/ov3Z7w1pwXMMISdcq0X CmkBLudpjLqOfv+LJLAAHgZSMAOwntplymB5St0mZV6gheeahYHsf0oKk1dEbckva2adI1sAtldg0 zSAfkyB5qESAnGy93JB4hhHc7vEiAIq1eGRa5uuHhV8Ye1zRG/hGSONknqFrN7KJDUsh41ixqVhCn 7pEMfWtuB6/0Rb4vY44mVDt1yIc9YleiwG15e+Ed80YgxVvmPu+KiZZx1W017yqrMNixeQtYjnRJr 5oOG8jA6fnQ2CMTbxf5k92qZOx0ViYm1r5jHbNCXCuZSKJ8sQ4SM5777oDp3S9kiK0I4V0eDj8DvU bbpZeGCQ==; Received: from [187.74.70.209] (helo=steammachine.lan) by fanzine2.igalia.com with esmtpsa (Cipher TLS1.3:ECDHE_X25519__RSA_PSS_RSAE_SHA256__AES_256_GCM:256) (Exim) id 1qHu8z-00AP6e-SZ; Sat, 08 Jul 2023 00:41:42 +0200 From: =?utf-8?q?Andr=C3=A9_Almeida?= To: dri-devel@lists.freedesktop.org, amd-gfx@lists.freedesktop.org, linux-kernel@vger.kernel.org, wayland-devel@lists.freedesktop.org Subject: [PATCH v5 6/6] drm/doc: Define KMS atomic state set Date: Fri, 7 Jul 2023 19:40:59 -0300 Message-ID: <20230707224059.305474-7-andrealmeid@igalia.com> X-Mailer: git-send-email 2.41.0 In-Reply-To: <20230707224059.305474-1-andrealmeid@igalia.com> References: <20230707224059.305474-1-andrealmeid@igalia.com> MIME-Version: 1.0 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?b?J01hcmVrIE9sxaE=?= =?utf-8?b?w6FrJw==?= , =?utf-8?q?Michel_D=C3=A4nzer?= , Randy Dunlap , Pekka Paalanen , hwentlan@amd.com, kernel-dev@igalia.com, alexander.deucher@amd.com, =?utf-8?q?Andr=C3=A9_Almeida?= , 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 Acked-by: Pekka Paalanen Reviewed-by: Daniel Vetter --- v4: total rework by Pekka --- Documentation/gpu/drm-uapi.rst | 41 ++++++++++++++++++++++++++++++++++ 1 file changed, 41 insertions(+) diff --git a/Documentation/gpu/drm-uapi.rst b/Documentation/gpu/drm-uapi.rst index 65fb3036a580..6a1662c08901 100644 --- a/Documentation/gpu/drm-uapi.rst +++ b/Documentation/gpu/drm-uapi.rst @@ -486,3 +486,44 @@ and the CRTC index is its position in this array. .. kernel-doc:: include/uapi/drm/drm_mode.h :internal: + +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 automatically avoid +no-operation changes, so it is safe and even expected for userspace to send +redundant property settings. 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. + +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.