MIPS: Loongson-3: Add PHYS48_TO_HT40 support

The width of HT-bus is only 40-bit, but Loongson-3 has 48-bit physical
address. This implies only node-0's memory is DMAable because high bits
(Node ID) will lost. Fortunately, by configuring address windows in
firmware, we can extract 2bit Node ID (bit 44~47, only bit 44~45 used
now) from Loongson-3's 48-bit address space and embed it into 40-bit
(bit 37~38). Every NUMA node can do DMA now (however, maximum memory of
each node is reduced to 2^37 = 128GB).

Signed-off-by: Huacai Chen <chenhc@lemote.com>
Cc: John Crispin <john@phrozen.org>
Cc: Steven J. Hill <Steven.Hill@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: Fuxin Zhang <zhangfx@lemote.com>
Cc: Zhangjin Wu <wuzhangjin@gmail.com>
Patchwork: https://patchwork.linux-mips.org/patch/8321/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
diff --git a/arch/mips/loongson/Kconfig b/arch/mips/loongson/Kconfig
index 1b91fc6..72f830ac 100644
--- a/arch/mips/loongson/Kconfig
+++ b/arch/mips/loongson/Kconfig
@@ -86,6 +86,7 @@
 	select LOONGSON_MC146818
 	select ZONE_DMA32
 	select LEFI_FIRMWARE_INTERFACE
+	select PHYS48_TO_HT40
 	help
 		Generic Loongson 3 family machines utilize the 3A/3B revision
 		of Loongson processor and RS780/SBX00 chipset.
@@ -131,6 +132,10 @@
 	select NEED_SG_DMA_LENGTH
 	select NEED_DMA_MAP_STATE
 
+config PHYS48_TO_HT40
+	bool
+	default y if CPU_LOONGSON3
+
 config LOONGSON_MC146818
 	bool
 	default n