[Intel-gfx] [PATCH] drm/i915: Fix __intel_wait_for_register_fw to not sleep in atomic

[Daniel Vetter]

On Wed, May 10, 2017 at 05:31:02PM +0200, Michal Wajdeczko wrote:
> On Wed, May 10, 2017 at 05:07:01PM +0200, Daniel Vetter wrote:
> > The unconditionally fallback to the blocking wait_for resulted in
> > impressive fireworks at boot-up on my snb here. Make sure if we set
> > the slow timeout to 0 that we never ever sleep. The tail of the
> > callchain was
> > 
> > intel_wait_for_register
> > -> __intel_wait_for_register_fw
> >   -> usleep_range
> >      -> BOOM
> > 
> > It blew up in intel_crt_detect load detection code on the
> > ADPA_CRT_HOTPLUG_FORCE_TRIGGER in the ADPA register.
> > 
> 
> Hmm, by reading the code, it looks that call stack should be like this:
> 
> -> intel_wait_for_register(..., timeout_ms=1000)
>   -> __intel_wait_for_register_fw(..., fast_us=2, slow_ms=0, NULL);
>   -> wait_for(..., MS=1000)
>     -> _wait_for(..., US=1000*1000, W=1000)
>       -> usleep_range(W, 2*W)
> 
> so the slow_timeout_ms will be 0 in __intel_wait_for_register_fw()
> 
> Are you sure that fix below is in right place?

The wait_for is _within the __intel_wait_for_register_fw. I've left out
the macros because those don't show up in the bt. We do _not_ blow up on
the wait_for after the __intel_wait_for_register_fw call in
intel_wait_for_register.
-Daniel

> 
> -Michal
> 
> 
> 
> > Fixes: 0564654340e2 ("drm/i915: Acquire uncore.lock over intel_uncore_wait_for_register()")
> > Cc: Chris Wilson <chris at chris-wilson.co.uk>
> > Cc: Michal Wajdeczko <michal.wajdeczko at intel.com>
> > Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
> > Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> > Cc: Daniel Vetter <daniel.vetter at intel.com>
> > Cc: Jani Nikula <jani.nikula at linux.intel.com>
> > Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>
> > Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
> > ---
> >  drivers/gpu/drm/i915/intel_uncore.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c
> > index aa9d3065853c..b03ad06bc3b6 100644
> > --- a/drivers/gpu/drm/i915/intel_uncore.c
> > +++ b/drivers/gpu/drm/i915/intel_uncore.c
> > @@ -1609,7 +1609,7 @@ int __intel_wait_for_register_fw(struct drm_i915_private *dev_priv,
> >  	ret = -ETIMEDOUT;
> >  	if (fast_timeout_us && fast_timeout_us <= 20000)
> >  		ret = _wait_for_atomic(done, fast_timeout_us, 0);
> > -	if (ret)
> > +	if (ret && slow_timeout_ms)
> >  		ret = wait_for(done, slow_timeout_ms);
> >  
> >  	if (out_value)
> > -- 
> > 2.5.5
> > 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch