[PATCH 3/6] drm/i915: Acquire uncore.lock over intel_uncore_wait_for_register()

[Chris Wilson]

We acquire the forcewake and use I915_READ_FW instead for the atomic
wait within intel_uncore_wait_for_register. However, this still leaves
us vulnerable to concurrent mmio access to the register, which can cause
system hangs on gen7. The protection is to acquire uncore.lock around
each register, so lets add it back.

v2: Wrap __intel_wait_for_register_fw() to re-use its atomic wait_for
loop and spare adding another for ourselves.
v3: Add might_sleep() annotation

Signed-off-by: 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>
---
 drivers/gpu/drm/i915/intel_uncore.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c
index 53c8457869f6..f43121700f83 100644
--- a/drivers/gpu/drm/i915/intel_uncore.c
+++ b/drivers/gpu/drm/i915/intel_uncore.c
@@ -1661,14 +1661,22 @@ int intel_wait_for_register(struct drm_i915_private *dev_priv,
 			    u32 value,
 			    unsigned int timeout_ms)
 {
-
 	unsigned fw =
 		intel_uncore_forcewake_for_reg(dev_priv, reg, FW_REG_READ);
 	int ret;
 
-	intel_uncore_forcewake_get(dev_priv, fw);
-	ret = wait_for_us((I915_READ_FW(reg) & mask) == value, 2);
-	intel_uncore_forcewake_put(dev_priv, fw);
+	might_sleep();
+
+	spin_lock_irq(&dev_priv->uncore.lock);
+	intel_uncore_forcewake_get__locked(dev_priv, fw);
+
+	ret = __intel_wait_for_register_fw(dev_priv,
+					   reg, mask, value,
+					   2, 0, NULL);
+
+	intel_uncore_forcewake_put__locked(dev_priv, fw);
+	spin_unlock_irq(&dev_priv->uncore.lock);
+
 	if (ret)
 		ret = wait_for((I915_READ_NOTRACE(reg) & mask) == value,
 			       timeout_ms);
-- 
2.11.0