From patchwork Fri Aug 18 20:06:42 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: 13358311 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 454A8EE4992 for ; Fri, 18 Aug 2023 20:07:02 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 58B3210E0F4; Fri, 18 Aug 2023 20:07:01 +0000 (UTC) Received: from fanzine2.igalia.com (fanzine2.igalia.com [213.97.179.56]) by gabe.freedesktop.org (Postfix) with ESMTPS id D785410E0E0; Fri, 18 Aug 2023 20:06:58 +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: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: In-Reply-To:References:List-Id:List-Help:List-Unsubscribe:List-Subscribe: List-Post:List-Owner:List-Archive; bh=txE0zVKMLpqBL3xL8Qe2oF2WCGKWdaX3pG7hx+/iU0g=; b=siisGlQYyHudwclbDpxOFEt5KT KTRlv4oTm8e0EOq5k65tEUWgHY2aqTHcdQitgct8L9ac3nuKS3vPO74Ys47+qRLHVOV+DEzCBMVxc K3FYnfuf2AvQHFVuTVL0bgi0+dj51GhMJEnZl5VBzViIc3Nju/+oM7PGDtFgPrRBnr/CGIodmsKnS hWnMR6Thb5hYf83gVUcqMhWP/YFFvVS7JuVtzyzIlrOexOWejyJ5h4MVOOsjN1hWUWZ9wQ5JuQIQt a38Cx18S4jDT3+yh3i3t5kXEYOX5u6jbFHfF2CofZX2unWbuOAKJ+T8nc1LGwFyXst7wl8LfLM5iG 40RfjT8Q==; Received: from [187.35.42.59] (helo=steammachine.lan) by fanzine2.igalia.com with esmtpsa (Cipher TLS1.3:ECDHE_X25519__RSA_PSS_RSAE_SHA256__AES_256_GCM:256) (Exim) id 1qX5kA-002iPJ-8e; Fri, 18 Aug 2023 22:06:50 +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 Subject: [PATCH v7] drm/doc: Document DRM device reset expectations Date: Fri, 18 Aug 2023 17:06:42 -0300 Message-ID: <20230818200642.276735-1-andrealmeid@igalia.com> X-Mailer: git-send-email 2.41.0 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, Randy Dunlap , =?utf-8?q?Andr=C3=A9_Almeida?= , =?utf-8?b?J01hcmVr?= =?utf-8?b?IE9sxaHDoWsn?= , =?utf-8?q?Michel_D=C3=A4nzer?= , =?utf-8?q?Timu?= =?utf-8?q?r_Krist=C3=B3f?= , Pekka Paalanen , Samuel Pitoiset , kernel-dev@igalia.com, alexander.deucher@amd.com, christian.koenig@amd.com Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" Create a section that specifies how to deal with DRM device resets for kernel and userspace drivers. Signed-off-by: André Almeida Acked-by: Sebastian Wick Acked-by: Pekka Paalanen --- v7 changes: - s/application/graphical API contex/ in the robustness part (Michel) - Grammar fixes (Randy) v6: https://lore.kernel.org/lkml/20230815185710.159779-1-andrealmeid@igalia.com/ v6 changes: - Due to substantial changes in the content, dropped Pekka's Acked-by - Grammar fixes (Randy) - Add paragraph about disabling device resets - Add note about integrating reset tracking in drm/sched - Add note that KMD should return failure for contexts affected by resets and UMD should check for this - Add note about lack of consensus around what to do about non-robust apps v5: https://lore.kernel.org/dri-devel/20230627132323.115440-1-andrealmeid@igalia.com/ --- Documentation/gpu/drm-uapi.rst | 77 ++++++++++++++++++++++++++++++++++ 1 file changed, 77 insertions(+) diff --git a/Documentation/gpu/drm-uapi.rst b/Documentation/gpu/drm-uapi.rst index 65fb3036a580..3694bdb977f5 100644 --- a/Documentation/gpu/drm-uapi.rst +++ b/Documentation/gpu/drm-uapi.rst @@ -285,6 +285,83 @@ for GPU1 and GPU2 from different vendors, and a third handler for mmapped regular files. Threads cause additional pain with signal handling as well. +Device reset +============ + +The GPU stack is really complex and is prone to errors, from hardware bugs, +faulty applications and everything in between the many layers. Some errors +require resetting the device in order to make the device usable again. This +section describes the expectations for DRM and usermode drivers when a +device resets and how to propagate the reset status. + +Device resets can not be disabled without tainting the kernel, which can lead to +hanging the entire kernel through shrinkers/mmu_notifiers. Userspace role in +device resets is to propagate the message to the application and apply any +special policy for blocking guilty applications, if any. Corollary is that +debugging a hung GPU context require hardware support to be able to preempt such +a GPU context while it's stopped. + +Kernel Mode Driver +------------------ + +The KMD is responsible for checking if the device needs a reset, and to perform +it as needed. Usually a hang is detected when a job gets stuck executing. KMD +should keep track of resets, because userspace can query any time about the +reset status for a specific context. This is needed to propagate to the rest of +the stack that a reset has happened. Currently, this is implemented by each +driver separately, with no common DRM interface. Ideally this should be properly +integrated at DRM scheduler to provide a common ground for all drivers. After a +reset, KMD should reject new command submissions for affected contexts. + +User Mode Driver +---------------- + +After command submission, UMD should check if the submission was accepted or +rejected. After a reset, KMD should reject submissions, and UMD can issue an +ioctl to the KMD to check the reset status, and this can be checked more often +if the UMD requires it. After detecting a reset, UMD will then proceed to report +it to the application using the appropriate API error code, as explained in the +section below about robustness. + +Robustness +---------- + +The only way to try to keep a graphical API context working after a reset is if +it complies with the robustness aspects of the graphical API that it is using. + +Graphical APIs provide ways to applications to deal with device resets. However, +there is no guarantee that the app will use such features correctly, and a +userspace that doesn't support robust interfaces (like a non-robust +OpenGL context or API without any robustness support like libva) leave the +robustness handling entirely to the userspace driver. There is no strong +community consensus on what the userspace driver should do in that case, +since all reasonable approaches have some clear downsides. + +OpenGL +~~~~~~ + +Apps using OpenGL should use the available robust interfaces, like the +extension ``GL_ARB_robustness`` (or ``GL_EXT_robustness`` for OpenGL ES). This +interface tells if a reset has happened, and if so, all the context state is +considered lost and the app proceeds by creating new ones. There's no consensus +on what to do to if robustness is not in use. + +Vulkan +~~~~~~ + +Apps using Vulkan should check for ``VK_ERROR_DEVICE_LOST`` for submissions. +This error code means, among other things, that a device reset has happened and +it needs to recreate the contexts to keep going. + +Reporting causes of resets +-------------------------- + +Apart from propagating the reset through the stack so apps can recover, it's +really useful for driver developers to learn more about what caused the reset in +the first place. DRM devices should make use of devcoredump to store relevant +information about the reset, so this information can be added to user bug +reports. + .. _drm_driver_ioctl: IOCTL Support on Device Nodes