Am 23.01.23 um 21:26 schrieb André Almeida:
Create a document that specifies how to deal with DRM device resets for
kernel and userspace drivers.
Signed-off-by: André Almeida <andrealmeid@xxxxxxxxxx>
---
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.
This is a pretty clear NAK from my side to this approach. The KMD should
never mess with an userspace process directly in such a way.
Instead use something like this "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``,
+ 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.
Again, pleas remove the "KMD kill" reference.
+
+Kernel mode driver
+------------------
+
+The KMD should be able to detect that something is wrong with the application
Please replace *should* with *must* here, this is mandatory or otherwise
core memory management can run into deadlocks during reclaim.
Regards,
Christian.
+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
