linux-kernel - [RFC PATCH] drm: Create documentation about device resets

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Message-Id: <20230123202646.356592-2-andrealmeid@igalia.com>
Date:   Mon, 23 Jan 2023 17:26:46 -0300
From:   André Almeida <andrealmeid@...lia.com>
To:     dri-devel@...ts.freedesktop.org, amd-gfx@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Cc:     kernel-dev@...lia.com, alexander.deucher@....com,
        contactshashanksharma@...il.com, amaranath.somalapuram@....com,
        christian.koenig@....com, pierre-eric.pelloux-prayer@....com,
        Simon Ser <contact@...rsion.fr>,
        Rob Clark <robdclark@...il.com>,
        Pekka Paalanen <ppaalanen@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Daniel Stone <daniel@...ishbar.org>,
        'Marek Olšák' <maraeo@...il.com>,
        Dave Airlie <airlied@...il.com>,
        "Pierre-Loup A . Griffais" <pgriffais@...vesoftware.com>,
        André Almeida <andrealmeid@...lia.com>
Subject: [RFC PATCH] drm: Create documentation about device resets

Create a document that specifies how to deal with DRM device resets for
kernel and userspace drivers.

Signed-off-by: André Almeida <andrealmeid@...lia.com>
---
 Documentation/gpu/drm-reset.rst | 51 +++++++++++++++++++++++++++++++++
 Documentation/gpu/index.rst     |  1 +
 2 files changed, 52 insertions(+)
 create mode 100644 Documentation/gpu/drm-reset.rst

diff --git a/Documentation/gpu/drm-reset.rst b/Documentation/gpu/drm-reset.rst
new file mode 100644
index 000000000000..0dd11a469cf9
--- /dev/null
+++ b/Documentation/gpu/drm-reset.rst
@@ -0,0 +1,51 @@
+================
+DRM Device Reset
+================
+
+The GPU stack is really complex and is prone to errors, from hardware bugs,
+faulty applications and everything in the many layers in between. To recover
+from this kind of state, sometimes is needed to reset the GPU. Unproper handling
+of GPU resets can lead to an unstable userspace. This page describes what's the
+expected behaviour from DRM drivers to do in those situations, from usermode
+drivers and compositors as well.
+
+Robustness
+----------
+
+First of all, application robust APIs, when available, should be used. This
+allows the application to correctly recover and continue to run after a reset.
+Apps that doesn't use this should be promptly killed when the kernel driver
+detects that it's in broken state. Specifically guidelines for some APIs:
+
+- OpenGL: During a reset, KMD kill processes that haven't ARB Robustness
+  enabled, assuming they can't recover.
+- Vulkan: Assumes that every app is able to deal with ``VK_ERROR_DEVICE_LOST``,
+  so KMD doesn't kill any. If it doesn't do it right, it's considered a broken
+  application and UMD will deal with it.
+
+Kernel mode driver
+------------------
+
+The KMD should be able to detect that something is wrong with the application
+and that a reset is needed to take place to recover the device (e.g. an endless
+wait). It needs to properly track the context that is broken and mark it as
+dead, so any other syscalls to that context should be further rejected. The
+other contexts should be preserved when possible, avoid crashing the rest of
+userspace. KMD can ban a file descriptor that keeps causing resets, as it's
+likely in a broken loop.
+
+User mode driver
+----------------
+
+During a reset, UMD should be aware that rejected syscalls indicates that the
+context is broken and for robust apps the recovery should happen for the
+context. Non-robust apps would be already terminated by KMD. If no new context
+is created for some time, it is assumed that the recovery didn't work, so UMD
+should terminate it.
+
+Compositors
+-----------
+
+(In the long term) compositors should be robust as well to properly deal with it
+errors. Init systems should be aware of the compositor status and reset it if is
+broken.
diff --git a/Documentation/gpu/index.rst b/Documentation/gpu/index.rst
index b99dede9a5b1..300b2529bd39 100644
--- a/Documentation/gpu/index.rst
+++ b/Documentation/gpu/index.rst
@@ -9,6 +9,7 @@ Linux GPU Driver Developer's Guide
    drm-mm
    drm-kms
    drm-kms-helpers
+   drm-reset
    drm-uapi
    drm-usage-stats
    driver-uapi
-- 
2.39.1