[RFC PATCH v3 1/4] 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 | 65 ++++++++++++++++++++++++++++++++++
 1 file changed, 65 insertions(+)

diff --git a/Documentation/gpu/drm-uapi.rst b/Documentation/gpu/drm-uapi.rst
index 65fb3036a580..da4f8a694d8d 100644
--- a/Documentation/gpu/drm-uapi.rst
+++ b/Documentation/gpu/drm-uapi.rst
@@ -285,6 +285,71 @@ 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. To recover
+from this kind of state, sometimes is needed to reset the device. This section
+describes what's the expectations for DRM and usermode drivers when a device
+resets and how to propagate the reset status.
+
+Kernel Mode Driver
+------------------
+
+The KMD is responsible for checking if the device needs a reset, and to perform
+it as needed. Usually a hung is detected when a job gets stuck executing. KMD
+then update it's internal reset tracking to be ready when userspace asks the
+kernel about reset information. Drivers should implement the DRM_IOCTL_GET_RESET
+for that.
+
+User Mode Driver
+----------------
+
+The UMD should check before submitting new commands to the KMD if the device has
+been reset, and this can be checked more often if it requires to. The
+DRM_IOCTL_GET_RESET is the default interface for those kind of checks. After
+detecting a reset, UMD will then proceed to report it to the application using
+the appropriated API error code, as explained in the bellow section about
+robustness.
+
+Robustness
+----------
+
+The only way to try to keep an application working after a reset is if it
+complies with the robustness aspects of the graphical API that is using.
+
+Graphical APIs provide ways to application to deal with device resets. However,
+there's no guarantee that the app will be correctly using such features, and UMD
+can implement policies to close the app if it's a repeating offender, likely in
+a broken loop. This is done to ensure that it doesn't keeps blocking the user
+interface to be correctly displayed.
+
+OpenGL
+~~~~~~
+
+Apps using OpenGL can rely on ``GL_ARB_robustness`` to be robust. This extension
+tells if a reset has happened, and if so, all the context state is considered
+lost and the app proceeds by creating new ones. If robustness isn't in use, UMD
+will terminate the app when a reset is detected, giving that the contexts are
+lost and the app won't be able to figure this out and recreate the contexts.
+
+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 resets causes
+-----------------------
+
+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
+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
-- 
2.41.0