Create a section that specifies how to deal with DRM device resets for kernel and userspace drivers. Signed-off-by: André Almeida <andrealmeid@xxxxxxxxxx> --- 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
