drm/i915: Acquire uncore.lock over intel_uncore_wait_for_register()

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@chris-wilson.co.uk>
Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170411101340.31994-3-chris@chris-wilson.co.uk
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c
index dded42db880b8587e7e8dda369e9f60a24ee3c9e..fb38c7692fc228f9b47c32f2362f42291e5bf8b1 100644 (file)
--- a/drivers/gpu/drm/i915/intel_uncore.c
+++ b/drivers/gpu/drm/i915/intel_uncore.c
@@ -1662,14 +1662,22 @@ 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);