Wouldn't the smal patch below solve the same issue in a simple way?
diff --git a/drivers/base/dma-coherent.c b/drivers/base/dma-coherent.c
index 640a7e63c453..e8f8447d705b 100644
--- a/drivers/base/dma-coherent.c
+++ b/drivers/base/dma-coherent.c
@@ -290,9 +290,11 @@ EXPORT_SYMBOL(dma_mmap_from_coherent);
static int rmem_dma_device_init(struct reserved_mem *rmem, struct device *dev)
{
struct dma_coherent_mem *mem = rmem->priv;
+ dma_addr_t dev_addr = ((rmem->base >> PAGE_SHIFT) -
+ dev->dma_pfn_offset) << PAGE_SHIFT;
if (!mem &&
- !dma_init_coherent_memory(rmem->base, rmem->base, rmem->size,
+ !dma_init_coherent_memory(rmem->base, dev_addr, rmem->size,
DMA_MEMORY_MAP | DMA_MEMORY_EXCLUSIVE,
&mem)) {
pr_err("Reserved memory: failed to init DMA memory pool at %pa,
size %ld MiB\n",
