DOORBELL_ADDR
region = iommu_alloc_resv_region(DOORBELL_ADDR,
msg->address_hi = upper_32_bits(DOORBELL_ADDR);
msg->address_lo = lower_32_bits(DOORBELL_ADDR);
BUILD_BUG_ON(upper_32_bits(DOORBELL_ADDR));
writel_relaxed(lower_32_bits(DOORBELL_ADDR),