[Intel-gfx] [PATCH] drm/i915: Only warn for might_sleep() before a slow wait_for_register

[Chris Wilson]

Quoting Pandiyan, Dhinakaran (2018-03-28 20:01:40)
> 
> On Wed, 2018-03-28 at 18:53 +0100, Chris Wilson wrote:
> > As intel_wait_for_register_fw() may use, and if successful only use, a
> > busy-wait loop, the might_sleep() warning is a little over-zealous.
> > Restrict it to a might_sleep_if() a slow timeout is specified (and so
> > the caller authorises use of a usleep).
> > 
> > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> > ---
> >  drivers/gpu/drm/i915/intel_uncore.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c
> > index f37ecfc69e49..44c4654443ba 100644
> > --- a/drivers/gpu/drm/i915/intel_uncore.c
> > +++ b/drivers/gpu/drm/i915/intel_uncore.c
> > @@ -1996,7 +1996,7 @@ int __intel_wait_for_register(struct drm_i915_private *dev_priv,
> >       u32 reg_value;
> >       int ret;
> >  
> > -     might_sleep();
> > +     might_sleep_if(slow_timeout_ms);
> 
> __wait_for() already has a might_sleep(), why is this needed?

To document that this routine is a sleeper, irrespective of the
implementation. Sometimes it is implicit on the implementation and so
should only be at the low level, sometimes we want to call out the
requirements explicitly and clearly. We have "wait" in the name so
shouting out that this may indeed sleep rather than busyspin seems to
be in order.
-Chris