MEMSWCTL
rgvswctl = I915_READ16(MEMSWCTL);
I915_WRITE16(MEMSWCTL, rgvswctl);
POSTING_READ16(MEMSWCTL);
I915_WRITE16(MEMSWCTL, rgvswctl);
if (wait_for_atomic((I915_READ(MEMSWCTL) & MEMCTL_CMD_STS) == 0, 10))
rgvswctl = I915_READ16(MEMSWCTL);
I915_WRITE(MEMSWCTL, rgvswctl);