Re: [PATCH] drm/i915: hangcheck timeout for debugfs

[Chris Wilson <chris@chris-wilson.co.uk>]

On Fri, 24 Jun 2011 08:46:53 -0700, Ben Widawsky <ben@bwidawsk.net> wrote:
> On Fri, Jun 24, 2011 at 12:48:22AM +0100, Chris Wilson wrote:
> > On Thu, 23 Jun 2011 15:49:14 -0700, Ben Widawsky <ben@bwidawsk.net> wrote:
> > > Provide a user accessible way to change the hangcheck timer. This is
> > > useful mostly for disabling the timer completely (value <= 0).
> > 
> > Having i915.hangcheck_interval as a read/write module parameter was
> > better. :-p
> > -Chris
> 
> I considered this, but I wasn't sure how to manage the sysfs parameters,
> and prevent users from doing stupid things. Furthermore, I think to be
> correct we must delete sync the timer if the user requests an interval
> of 0, and we can only do that if we have struct mutex (again the sysfs
> problem).

You can either register a callback for when the parameter changes, but in
this case it is as easy as deleting the timer in the next hangcheck before
touching any GPU state. In that scenario the timer will only be enabled
again after the next execbuffers, that's a restriction I can live with for
simple code and keeping parameters out of debugfs.

On the other hand, a debugfs would allow for a per-device parameter. For
that day in the far far future with multiprocessor igfx. Surreal isn't it?
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre