MIPS: Loongson-3: Introduce CONFIG_LOONGSON3_ENHANCEMENT

New Loongson 3 CPU (since Loongson-3A R2, as opposed to Loongson-3A R1,
Loongson-3B R1 and Loongson-3B R2) has many enhancements, such as FTLB,
L1-VCache, EI/DI/Wait/Prefetch instruction, DSP/DSPv2 ASE, User Local
register, Read-Inhibit/Execute-Inhibit, SFB (Store Fill Buffer), Fast
TLB refill support, etc.

This patch introduce a config option, CONFIG_LOONGSON3_ENHANCEMENT, to
enable those enhancements which are not probed at run time. If you want
a generic kernel to run on all Loongson 3 machines, please say 'N'
here. If you want a high-performance kernel to run on new Loongson 3
machines only, please say 'Y' here.

Some additional explanations:
1) SFB locates between core and L1 cache, it causes memory access out
   of order, so writel/outl (and other similar functions) need a I/O
   reorder barrier.
2) Loongson 3 has a bug that di instruction can not save the irqflag,
   so arch_local_irq_save() is modified. Since CPU_MIPSR2 is selected
   by CONFIG_LOONGSON3_ENHANCEMENT, generic kernel doesn't use ei/di
   at all.
3) CPU_HAS_PREFETCH is selected by CONFIG_LOONGSON3_ENHANCEMENT, so
   MIPS_CPU_PREFETCH (used by uasm) probing is also put in this patch.

Signed-off-by: Huacai Chen <chenhc@lemote.com>
Cc: Aurelien Jarno <aurelien@aurel32.net>
Cc: Steven J . Hill <sjhill@realitydiluted.com>
Cc: Fuxin Zhang <zhangfx@lemote.com>
Cc: Zhangjin Wu <wuzhangjin@gmail.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/12755/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index adcc97e..d5c3621 100644
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -1360,6 +1360,24 @@
 		The Loongson 3 processor implements the MIPS64R2 instruction
 		set with many extensions.
 
+config LOONGSON3_ENHANCEMENT
+	bool "New Loongson 3 CPU Enhancements"
+	default n
+	select CPU_MIPSR2
+	select CPU_HAS_PREFETCH
+	depends on CPU_LOONGSON3
+	help
+	  New Loongson 3 CPU (since Loongson-3A R2, as opposed to Loongson-3A
+	  R1, Loongson-3B R1 and Loongson-3B R2) has many enhancements, such as
+	  FTLB, L1-VCache, EI/DI/Wait/Prefetch instruction, DSP/DSPv2 ASE, User
+	  Local register, Read-Inhibit/Execute-Inhibit, SFB (Store Fill Buffer),
+	  Fast TLB refill support, etc.
+
+	  This option enable those enhancements which are not probed at run
+	  time. If you want a generic kernel to run on all Loongson 3 machines,
+	  please say 'N' here. If you want a high-performance kernel to run on
+	  new Loongson 3 machines only, please say 'Y' here.
+
 config CPU_LOONGSON2E
 	bool "Loongson 2E"
 	depends on SYS_HAS_CPU_LOONGSON2E