[PATCH v2 1/1] drm/doc: Document DRM device reset expectations

[André Almeida]

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

Signed-off-by: André Almeida <andrealmeid at igalia.com>
---
 Documentation/gpu/drm-uapi.rst | 51 ++++++++++++++++++++++++++++++++++
 1 file changed, 51 insertions(+)

diff --git a/Documentation/gpu/drm-uapi.rst b/Documentation/gpu/drm-uapi.rst
index 65fb3036a580..3d6c3ed392ea 100644
--- a/Documentation/gpu/drm-uapi.rst
+++ b/Documentation/gpu/drm-uapi.rst
@@ -285,6 +285,57 @@ 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 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 section describes what's
+the expected behaviour from DRM drivers to do in those situations, from usermode
+drivers and compositors as well. The end goal is to have a seamless experience
+as possible, either the stack being able to recover itself or resetting to a new
+stable state.
+
+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: KMD signals the abortion of submitted commands and the UMD should then
+  react accordingly and abort the application.
+
+- Vulkan: Assumes that every app is able to deal with ``VK_ERROR_DEVICE_LOST``.
+  If it doesn't do it right, it's considered a broken application and UMD will
+  deal with it, aborting it.
+
+Kernel mode driver
+------------------
+
+The KMD must 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 must be terminated.
+
+Compositors
+-----------
+
+Compositors should be robust as well to properly deal with its errors.
+
+
 .. _drm_driver_ioctl:
 
 IOCTL Support on Device Nodes
-- 
2.39.2