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

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

[Daniel Vetter]

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.

Fixes: 0564654340e2 ("drm/i915: Acquire uncore.lock over intel_uncore_wait_for_register()")
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Daniel Vetter <daniel.vetter@intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@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

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✗ Fi.CI.BAT: failure for drm/i915: Fix __intel_wait_for_register_fw to not sleep in atomic

[Patchwork]

== Series Details ==

Series: drm/i915: Fix __intel_wait_for_register_fw to not sleep in atomic
URL   : https://patchwork.freedesktop.org/series/24229/
State : failure

== Summary ==

  CHK     include/config/kernel.release
  CHK     include/generated/uapi/linux/version.h
  CHK     include/generated/utsrelease.h
  CHK     include/generated/bounds.h
  CHK     include/generated/timeconst.h
  CHK     include/generated/asm-offsets.h
  CALL    scripts/checksyscalls.sh
  CHK     include/generated/compile.h
  CHK     kernel/config_data.h
  CC [M]  drivers/gpu/drm/i915/intel_uncore.o
drivers/gpu/drm/i915/intel_uncore.c: In function ‘__intel_wait_for_register_fw’:
drivers/gpu/drm/i915/intel_uncore.c:1628:14: error: ‘reg_value’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
   *out_value = reg_value;
              ^
cc1: all warnings being treated as errors
scripts/Makefile.build:294: recipe for target 'drivers/gpu/drm/i915/intel_uncore.o' failed
make[4]: *** [drivers/gpu/drm/i915/intel_uncore.o] Error 1
scripts/Makefile.build:553: recipe for target 'drivers/gpu/drm/i915' failed
make[3]: *** [drivers/gpu/drm/i915] Error 2
scripts/Makefile.build:553: recipe for target 'drivers/gpu/drm' failed
make[2]: *** [drivers/gpu/drm] Error 2
scripts/Makefile.build:553: recipe for target 'drivers/gpu' failed
make[1]: *** [drivers/gpu] Error 2
Makefile:1002: recipe for target 'drivers' failed
make: *** [drivers] Error 2

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Re: [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@chris-wilson.co.uk>
> Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> Cc: Daniel Vetter <daniel.vetter@intel.com>
> Cc: Jani Nikula <jani.nikula@linux.intel.com>
> Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
> Signed-off-by: Daniel Vetter <daniel.vetter@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
> 
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Re: [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@chris-wilson.co.uk>
> > Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
> > Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> > Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> > Cc: Daniel Vetter <daniel.vetter@intel.com>
> > Cc: Jani Nikula <jani.nikula@linux.intel.com>
> > Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
> > Signed-off-by: Daniel Vetter <daniel.vetter@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
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Re: [PATCH] drm/i915: Fix __intel_wait_for_register_fw to not sleep in atomic

[Michal Wajdeczko]

On Wed, May 10, 2017 at 05:32:48PM +0200, Daniel Vetter wrote:
> 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.

Ok, so the correct call stack is

-> intel_wait_for_register(..., timeout_ms=1000)
  -> __intel_wait_for_register_fw(..., fast_us=2, slow_ms=0, NULL);
    -> wait_for(..., MS=0)
      -> _wait_for(..., US=0, W=1000)
        -> usleep_range(W, 2*W)

so maybe we should just fix the wait_for/_wait_for macros and do not attempt
to sleep when timeout is zero ? It's rather unexpected that even with with
timeout MS=0 we will still call usleep_range(1000us, 2000us)

-Michal

> -Daniel
> 
> > 
> > -Michal
> > 
> > 
> > 
> > > Fixes: 0564654340e2 ("drm/i915: Acquire uncore.lock over intel_uncore_wait_for_register()")
> > > Cc: Chris Wilson <chris@chris-wilson.co.uk>
> > > Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
> > > Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> > > Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> > > Cc: Daniel Vetter <daniel.vetter@intel.com>
> > > Cc: Jani Nikula <jani.nikula@linux.intel.com>
> > > Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
> > > Signed-off-by: Daniel Vetter <daniel.vetter@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
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Re: [PATCH] drm/i915: Fix __intel_wait_for_register_fw to not sleep in atomic

[Chris Wilson]

On Wed, May 10, 2017 at 05:49:26PM +0200, Michal Wajdeczko wrote:
> On Wed, May 10, 2017 at 05:32:48PM +0200, Daniel Vetter wrote:
> > 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.
> 
> Ok, so the correct call stack is
> 
> -> intel_wait_for_register(..., timeout_ms=1000)
>   -> __intel_wait_for_register_fw(..., fast_us=2, slow_ms=0, NULL);
>     -> wait_for(..., MS=0)
>       -> _wait_for(..., US=0, W=1000)
>         -> usleep_range(W, 2*W)
> 
> so maybe we should just fix the wait_for/_wait_for macros and do not attempt
> to sleep when timeout is zero ? It's rather unexpected that even with with
> timeout MS=0 we will still call usleep_range(1000us, 2000us)

In this case, it was clearly incorrect to do a wait_for_pass at all. In
general, those wait_for macros are already complicated enough and the
callers of wait_for() must reasonably expect it to sleep and so a seperate
dance for timeout==0 seems unjustified.
-Chris

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

[Michal Wajdeczko]

On Wed, May 10, 2017 at 05:09:17PM +0100, Chris Wilson wrote:
> On Wed, May 10, 2017 at 05:49:26PM +0200, Michal Wajdeczko wrote:
> > On Wed, May 10, 2017 at 05:32:48PM +0200, Daniel Vetter wrote:
> > > 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.
> > 
> > Ok, so the correct call stack is
> > 
> > -> intel_wait_for_register(..., timeout_ms=1000)
> >   -> __intel_wait_for_register_fw(..., fast_us=2, slow_ms=0, NULL);
> >     -> wait_for(..., MS=0)
> >       -> _wait_for(..., US=0, W=1000)
> >         -> usleep_range(W, 2*W)
> > 
> > so maybe we should just fix the wait_for/_wait_for macros and do not attempt
> > to sleep when timeout is zero ? It's rather unexpected that even with with
> > timeout MS=0 we will still call usleep_range(1000us, 2000us)
> 
> In this case, it was clearly incorrect to do a wait_for_pass at all. In
> general, those wait_for macros are already complicated enough and the

Maybe no extra dance is needed, just this:

 #define _wait_for(COND, US, W) ({ \
-       unsigned long timeout__ = jiffies + usecs_to_jiffies(US) + 1;   \
+       unsigned long timeout__ = jiffies + usecs_to_jiffies(US);       \
        int ret__;                                                      \
        for (;;) {                                                      \
                bool expired__ = time_after(jiffies, timeout__);        \

-Michal

> callers of wait_for() must reasonably expect it to sleep and so a seperate
> dance for timeout==0 seems unjustified.
> -Chris
> 
> -- 
> Chris Wilson, Intel Open Source Technology Centre
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Re: [PATCH] drm/i915: Fix __intel_wait_for_register_fw to not sleep in atomic

[Daniel Vetter]

On Wed, May 10, 2017 at 05:06:38PM +0100, Chris Wilson wrote:
> On Wed, May 10, 2017 at 05:19:32PM +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.
> > 
> > v2: Shut up gcc.
> 
> u32 uninitialized_var(reg_value) ?

Polished to v3 and applied, thanks for your review.
-Daniel
-- 
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Software Engineer, Intel Corporation
http://blog.ffwll.ch
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Re: [PATCH] drm/i915: Fix __intel_wait_for_register_fw to not sleep in atomic

[Chris Wilson]

On Wed, May 10, 2017 at 05:19:32PM +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.
> 
> v2: Shut up gcc.

u32 uninitialized_var(reg_value) ?
-Chris

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

[Daniel Vetter]

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.

v2: Shut up gcc.

Fixes: 0564654340e2 ("drm/i915: Acquire uncore.lock over intel_uncore_wait_for_register()")
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Daniel Vetter <daniel.vetter@intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
---
 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 aa9d3065853c..08abb2cb7837 100644
--- a/drivers/gpu/drm/i915/intel_uncore.c
+++ b/drivers/gpu/drm/i915/intel_uncore.c
@@ -1598,7 +1598,7 @@ int __intel_wait_for_register_fw(struct drm_i915_private *dev_priv,
 				 unsigned int slow_timeout_ms,
 				 u32 *out_value)
 {
-	u32 reg_value;
+	u32 reg_value = 0;
 #define done (((reg_value = I915_READ_FW(reg)) & mask) == value)
 	int ret;
 
@@ -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

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