Re: [PATCH v4 1/3] drm: Introduce device wedged event

[Matt Roper <matthew.d.roper@intel.com>]

On Fri, Sep 06, 2024 at 03:12:23PM +0530, Raag Jadav wrote:
> Introduce device wedged event, which will notify userspace of wedged
> (hanged/unusable) state of the DRM device through a uevent. This is
> useful especially in cases where the device is in unrecoverable state
> and requires userspace intervention for recovery.
> 
> Purpose of this implementation is to be vendor agnostic. Userspace
> consumers (sysadmin) can define udev rules to parse this event and
> take respective action to recover the device.
> 
> Consumer expectations:
> ----------------------
> 1) Unbind driver
> 2) Reset bus device
> 3) Re-bind driver
> 
> v4: s/drm_dev_wedged/drm_dev_wedged_event
>     Use drm_info() (Jani)
>     Kernel doc adjustment (Aravind)
> 
> Signed-off-by: Raag Jadav <raag.jadav@intel.com>
> ---
>  drivers/gpu/drm/drm_drv.c | 20 ++++++++++++++++++++
>  include/drm/drm_drv.h     |  1 +
>  2 files changed, 21 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
> index 93543071a500..cca5d8295eb7 100644
> --- a/drivers/gpu/drm/drm_drv.c
> +++ b/drivers/gpu/drm/drm_drv.c
> @@ -499,6 +499,26 @@ void drm_dev_unplug(struct drm_device *dev)
>  }
>  EXPORT_SYMBOL(drm_dev_unplug);
>  
> +/**
> + * drm_dev_wedged_event - generate a device wedged uevent
> + * @dev: DRM device
> + *
> + * This generates a device wedged uevent for the DRM device specified by @dev,
> + * on the basis of which, userspace may take respective action to recover the
> + * device. Currently we only set WEDGED=1 in the uevent environment, but this
> + * can be expanded in the future.

Just to clarify, is "wedged" intended to always mean "the entire device
is unusable" or are there cases where it would also get sent if only
part of the device is in a bad state?  For example, using i915/Xe
terminology, maybe the GT is dead but display is still working.  Or one
GT is dead, but another is still alive.

Basically, is this event intended as a signal that userspace should stop
trying to do _anything_ with the device, or just that the device has
degraded functionality in some way (and maybe userspace can still do
something useful if it's lucky)?  It would be good to clarify that in
the docs here in case different drivers have different ideas about how
this is expected to work.


Matt

> + */
> +void drm_dev_wedged_event(struct drm_device *dev)
> +{
> +	char *event_string = "WEDGED=1";
> +	char *envp[] = { event_string, NULL };
> +
> +	drm_info(dev, "device wedged, generating uevent\n");
> +
> +	kobject_uevent_env(&dev->primary->kdev->kobj, KOBJ_CHANGE, envp);
> +}
> +EXPORT_SYMBOL(drm_dev_wedged_event);
> +
>  /*
>   * DRM internal mount
>   * We want to be able to allocate our own "struct address_space" to control
> diff --git a/include/drm/drm_drv.h b/include/drm/drm_drv.h
> index cd37936c3926..eed5e54c74fd 100644
> --- a/include/drm/drm_drv.h
> +++ b/include/drm/drm_drv.h
> @@ -489,6 +489,7 @@ void drm_put_dev(struct drm_device *dev);
>  bool drm_dev_enter(struct drm_device *dev, int *idx);
>  void drm_dev_exit(int idx);
>  void drm_dev_unplug(struct drm_device *dev);
> +void drm_dev_wedged_event(struct drm_device *dev);
>  
>  /**
>   * drm_dev_is_unplugged - is a DRM device unplugged
> -- 
> 2.34.1
> 

-- 
Matt Roper
Graphics Software Engineer
Linux GPU Platform Enablement
Intel Corporation