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. + +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
