[Intel-gfx] [PATCH] drm/i915: Clear pending reset requests during suspend

[Daniel Vetter]

On Tue, Jan 19, 2016 at 01:48:05PM +0000, Chris Wilson wrote:
> On Tue, Jan 19, 2016 at 01:09:28PM +0100, Daniel Vetter wrote:
> > On Thu, Jan 14, 2016 at 10:49:45AM +0000, Arun Siluvery wrote:
> > > Pending reset requests are cleared before suspending, they should be picked up
> > > after resume when new work is submitted.
> > > 
> > > This is originally added as part of TDR patches for Gen8 from Tomas Elf which
> > > are under review, as suggested by Chris this is extracted as a separate patch
> > > as it can be useful now.
> > > 
> > > Cc: Mika Kuoppala <mika.kuoppala at intel.com>
> > > Cc: Chris Wilson <chris at chris-wilson.co.uk>
> > > Signed-off-by: Arun Siluvery <arun.siluvery at linux.intel.com>
> > 
> > Pulling in the discussion we had from irc: Imo the right approach is to
> > simply wait for gpu reset to finish it's job. Since that could in turn
> > lead to a dead gpu (if we're unlucky and init_hw failed) we'd need to do
> > that in a loop around gem_idle. And drop dev->struct_mutex in-between.
> > E.g.
> > 
> > while (busy) {
> > 	mutex_lock();
> > 	gpu_idle();
> > 	mutex_unlock();
> > 
> > 	flush_work(reset_work);
> > }
> 
> Where does the requirement for gpu_idle come from? If there is a global
> reset in progress, it cannot queue a request to flush the work and
> waiting on the old results will be skipped. So just wait for the global
> reset to complete, i.e. flush_work().

Yes, but the global reset might in turn leave a wrecked gpu behind, or at
least a non-idle one. Hence another gpu_idle on top, to make sure. If we
change init_hw() of engines to be synchronous then we should have at least
a WARN_ON(not_idle_but_i_expected_so()); in there ...
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch