[PATCH v9 1/4] drm: Introduce device wedged event

[Raag Jadav]

On Mon, Nov 18, 2024 at 08:26:37PM +0530, Aravind Iddamsetty wrote:
> On 15/11/24 10:37, Raag Jadav wrote:
> > Introduce device wedged event, which notifies userspace of 'wedged'
> > (hanged/unusable) state of the DRM device through a uevent. This is
> > useful especially in cases where the device is no longer operating as
> > expected and has become unrecoverable from driver context. Purpose of
> > this implementation is to provide drivers a generic way to recover with
> > the help of userspace intervention without taking any drastic measures
> > in the driver.
> >
> > A 'wedged' device is basically a dead device that needs attention. The
> > uevent is the notification that is sent to userspace along with a hint
> > about what could possibly be attempted to recover the device and bring
> > it back to usable state. Different drivers may have different ideas of
> > a 'wedged' device depending on their hardware implementation, and hence
> > the vendor agnostic nature of the event. It is up to the drivers to
> > decide when they see the need for recovery and how they want to recover
> > from the available methods.
> >
> > Prerequisites
> > -------------
> >
> > The driver, before opting for recovery, needs to make sure that the
> > 'wedged' device doesn't harm the system as a whole by taking care of the
> > prerequisites. Necessary actions must include disabling DMA to system
> > memory as well as any communication channels with other devices. Further,
> > the driver must ensure that all dma_fences are signalled and any device
> > state that the core kernel might depend on are cleaned up. Once the event
> > is sent, the device must be kept in 'wedged' state until the recovery is
> > performed. New accesses to the device (IOCTLs) should be blocked,
> > preferably with an error code that resembles the type of failure the
> > device has encountered. This will signify the reason for wegeding which
> > can be reported to the application if needed.
> 
> should we even drop the mmaps we created?

Whatever is required for a clean recovery, yes.

Although how would this play out? Do we risk loosing display?
Or any other possible side-effects?

Raag