SDEIER
sde_ier = I915_READ(SDEIER);
I915_WRITE(SDEIER, 0);
I915_WRITE(SDEIER, sde_ier);
WARN_ON(I915_READ(SDEIER) != 0);
I915_WRITE(SDEIER, 0xffffffff);
POSTING_READ(SDEIER);
WARN_ON(I915_READ(SDEIER) != 0);
I915_WRITE(SDEIER, 0xffffffff);
POSTING_READ(SDEIER);