riscv: add ZONE_DMA32

This patch allows devices that require memory that can be addressed
using 32-bit addresses to work easily on RISC-V systems.  The newly
improved dma-direct ops will tap into this pool automatically for
32-bit addressing.

Based on an earlier patch from Wesley W. Terpstra.

CC: Wesley W. Terpstra <terpstra@sifive.com>
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NPalmer Dabbelt <palmer@sifive.com>

arch/riscv/Kconfig

@@ -22,6 +22,7 @@ config RISCV
 	select GENERIC_ATOMIC64 if !64BIT || !RISCV_ISA_A
 	select ARCH_WANT_OPTIONAL_GPIOLIB
 	select HAVE_MEMBLOCK
+	select HAVE_MEMBLOCK_NODE_MAP
 	select HAVE_DMA_API_DEBUG
 	select HAVE_DMA_CONTIGUOUS
 	select HAVE_GENERIC_DMA_COHERENT
@@ -43,6 +44,10 @@ config MMU
 config ARCH_PHYS_ADDR_T_64BIT
 	def_bool y
 
+config ZONE_DMA32
+	bool
+	default y
+
 config ARCH_DMA_ADDR_T_64BIT
 	def_bool y
 

arch/riscv/kernel/setup.c

@@ -181,6 +181,15 @@ static void __init setup_bootmem(void)
 	early_init_fdt_scan_reserved_mem();
 	memblock_allow_resize();
 	memblock_dump_all();
+
+	for_each_memblock(memory, reg) {
+		unsigned long start_pfn = memblock_region_memory_base_pfn(reg);
+		unsigned long end_pfn = memblock_region_memory_end_pfn(reg);
+
+		memblock_set_node(PFN_PHYS(start_pfn),
+		                  PFN_PHYS(end_pfn - start_pfn),
+		                  &memblock.memory, 0);
+	}
 }
 
 void __init setup_arch(char **cmdline_p)

arch/riscv/mm/init.c

@@ -17,6 +17,7 @@
 #include <linux/initrd.h>
 #include <linux/memblock.h>
 #include <linux/swap.h>
+#include <linux/sizes.h>
 
 #include <asm/tlbflush.h>
 #include <asm/sections.h>
@@ -25,11 +26,12 @@
 
 static void __init zone_sizes_init(void)
 {
-	unsigned long zones_size[MAX_NR_ZONES];
+	unsigned long max_zone_pfns[MAX_NR_ZONES] = { 0, };
 
-	memset(zones_size, 0, sizeof(zones_size));
-	zones_size[ZONE_NORMAL] = max_mapnr;
-	free_area_init_node(0, zones_size, pfn_base, NULL);
+	max_zone_pfns[ZONE_DMA32] = PFN_DOWN(min(4UL * SZ_1G, max_low_pfn));
+	max_zone_pfns[ZONE_NORMAL] = max_low_pfn;
+
+	free_area_init_nodes(max_zone_pfns);
 }
 
 void setup_zero_page(void)