arm64: Limit the CMA buffer to 32-bit if ZONE_DMA

When the CMA buffer is allocated, it is too early to know whether
devices will require ZONE_DMA memory. This patch limits the CMA buffer
to (DMA_BIT_MASK(32) + 1) if CONFIG_ZONE_DMA is enabled.

In addition, it computes the dma_to_phys(DMA_BIT_MASK(32)) before the
increment (no current functional change).
Signed-off-by: NCatalin Marinas <catalin.marinas@arm.com>

arch/arm64/mm/init.c

@@ -71,7 +71,7 @@ static void __init zone_sizes_init(unsigned long min, unsigned long max)
 	/* 4GB maximum for 32-bit only capable devices */
 	if (IS_ENABLED(CONFIG_ZONE_DMA)) {
 		unsigned long max_dma_phys =
-			(unsigned long)dma_to_phys(NULL, DMA_BIT_MASK(32) + 1);
+			(unsigned long)(dma_to_phys(NULL, DMA_BIT_MASK(32)) + 1);
 		max_dma = max(min, min(max, max_dma_phys >> PAGE_SHIFT));
 		zone_size[ZONE_DMA] = max_dma - min;
 	}
@@ -126,6 +126,8 @@ static void arm64_memory_present(void)
 
 void __init arm64_memblock_init(void)
 {
+	phys_addr_t dma_phys_limit = 0;
+
 	/* Register the kernel text, kernel data and initrd with memblock */
 	memblock_reserve(__pa(_text), _end - _text);
 #ifdef CONFIG_BLK_DEV_INITRD
@@ -141,7 +143,11 @@ void __init arm64_memblock_init(void)
 	memblock_reserve(__pa(idmap_pg_dir), IDMAP_DIR_SIZE);
 
 	early_init_fdt_scan_reserved_mem();
-	dma_contiguous_reserve(0);
+
+	/* 4GB maximum for 32-bit only capable devices */
+	if (IS_ENABLED(CONFIG_ZONE_DMA))
+		dma_phys_limit = dma_to_phys(NULL, DMA_BIT_MASK(32)) + 1;
+	dma_contiguous_reserve(dma_phys_limit);
 
 	memblock_allow_resize();
 	memblock_dump_all();