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

[Michal Wajdeczko]

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?

-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
>