On Tue, Jun 27, 2023 at 3:23 PM André Almeida <andrealmeid@xxxxxxxxxx> wrote: > > Create a section that specifies how to deal with DRM device resets for > kernel and userspace drivers. > > Acked-by: Pekka Paalanen <pekka.paalanen@xxxxxxxxxxxxx> > Signed-off-by: André Almeida <andrealmeid@xxxxxxxxxx> > --- > > v4: https://lore.kernel.org/lkml/20230626183347.55118-1-andrealmeid@xxxxxxxxxx/ > > Changes: > - Grammar fixes (Randy) > > Documentation/gpu/drm-uapi.rst | 68 ++++++++++++++++++++++++++++++++++ > 1 file changed, 68 insertions(+) > > diff --git a/Documentation/gpu/drm-uapi.rst b/Documentation/gpu/drm-uapi.rst > index 65fb3036a580..3cbffa25ed93 100644 > --- a/Documentation/gpu/drm-uapi.rst > +++ b/Documentation/gpu/drm-uapi.rst > @@ -285,6 +285,74 @@ 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 > +sections describes 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 hang is detected when a job gets stuck executing. KMD > +should keep track of resets, because userspace can query any time about the > +reset stats for an 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. > + > +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 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 an application 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 the > +UMD can implement policies to close the app if it is a repeating offender, > +likely in a broken loop. This is done to ensure that it does not keep blocking > +the user interface from being correctly displayed. This should be done even if > +the app is correct but happens to trigger some bug in the hardware/driver. I still don't think it's good to let the kernel arbitrarily kill processes that it thinks are not well-behaved based on some heuristics and policy. Can't this be outsourced to user space? Expose the information about processes causing a device and let e.g. systemd deal with coming up with a policy and with killing stuff. > + > +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. If it is possible to > +determine that robustness is not in use, the 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 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 > +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 >
