[Intel-gfx] [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 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 | 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