riscv: Only initialize swiotlb when necessary

The SWIOTLB buffer is not needed unless the physical address space
is beyond the limit of dma, only initialize swiotlb when swiotlb_force
is true or not all system memory is DMA-able.

Also move the swiotlb_init() into mem_init().
Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>

arch/riscv/kernel/setup.c

@@ -17,7 +17,6 @@
 #include <linux/of_fdt.h>
 #include <linux/of_platform.h>
 #include <linux/sched/task.h>
-#include <linux/swiotlb.h>
 #include <linux/smp.h>
 #include <linux/efi.h>
 #include <linux/crash_dump.h>
@@ -295,10 +294,6 @@ void __init setup_arch(char **cmdline_p)
 		protect_kernel_linear_mapping_text_rodata();
 	}
 
-#ifdef CONFIG_SWIOTLB
-	swiotlb_init(1);
-#endif
-
 #ifdef CONFIG_KASAN
 	kasan_init();
 #endif

arch/riscv/mm/init.c

@@ -11,6 +11,7 @@
 #include <linux/memblock.h>
 #include <linux/initrd.h>
 #include <linux/swap.h>
+#include <linux/swiotlb.h>
 #include <linux/sizes.h>
 #include <linux/of_fdt.h>
 #include <linux/of_reserved_mem.h>
@@ -109,6 +110,13 @@ void __init mem_init(void)
 	BUG_ON(!mem_map);
 #endif /* CONFIG_FLATMEM */
 
+#ifdef CONFIG_SWIOTLB
+	if (swiotlb_force == SWIOTLB_FORCE ||
+	    max_pfn > PFN_DOWN(dma32_phys_limit))
+		swiotlb_init(1);
+	else
+		swiotlb_force = SWIOTLB_NO_FORCE;
+#endif
 	high_memory = (void *)(__va(PFN_PHYS(max_low_pfn)));
 	memblock_free_all();