MIPS: Add LLB bit and related feature for the Config 5 CP0 register

The LLBIT (bit 4) in the Config5 CP0 register indicates the software
availability of the Load-Linked bit. This bit is only set by hardware
and it has the following meaning:

0: LLB functionality is not supported
1: LLB functionality is supported. The following feature are also
supported:

- ERETNC instruction. Similar to ERET but it does not clear the LLB
bit in the LLAddr register.
- CP0 LLAddr/LLB bit must be set
- LLbit is software accessible through the LLAddr[0]

This will be used later on to emulate R2 LL/SC instructions.

Signed-off-by: Markos Chandras <[email protected]>

arch/mips/include/asm/cpu-features.h

@@ -38,6 +38,9 @@
 #ifndef cpu_has_maar
 #define cpu_has_maar		(cpu_data[0].options & MIPS_CPU_MAAR)
 #endif
+#ifndef cpu_has_rw_llb
+#define cpu_has_rw_llb		(cpu_data[0].options & MIPS_CPU_RW_LLB)
+#endif
 
 /*
  * For the moment we don't consider R6000 and R8000 so we can assume that

arch/mips/include/asm/cpu.h

@@ -376,6 +376,7 @@ enum cpu_type_enum {
 #define MIPS_CPU_RIXIEX		0x200000000ull /* CPU has unique exception codes for {Read, Execute}-Inhibit exceptions */
 #define MIPS_CPU_MAAR		0x400000000ull /* MAAR(I) registers are present */
 #define MIPS_CPU_FRE		0x800000000ull /* FRE & UFE bits implemented */
+#define MIPS_CPU_RW_LLB		0x1000000000ull /* LLADDR/LLB writes are allowed */
 
 /*
  * CPU ASE encodings

arch/mips/include/asm/mipsregs.h

@@ -653,6 +653,7 @@
 #define MIPS_CONF5_NF		(_ULCAST_(1) << 0)
 #define MIPS_CONF5_UFR		(_ULCAST_(1) << 2)
 #define MIPS_CONF5_MRP		(_ULCAST_(1) << 3)
+#define MIPS_CONF5_LLB		(_ULCAST_(1) << 4)
 #define MIPS_CONF5_MVH		(_ULCAST_(1) << 5)
 #define MIPS_CONF5_FRE		(_ULCAST_(1) << 8)
 #define MIPS_CONF5_UFE		(_ULCAST_(1) << 9)

arch/mips/kernel/cpu-probe.c

@@ -514,6 +514,8 @@ static inline unsigned int decode_config5(struct cpuinfo_mips *c)
 		c->options |= MIPS_CPU_EVA;
 	if (config5 & MIPS_CONF5_MRP)
 		c->options |= MIPS_CPU_MAAR;
+	if (config5 & MIPS_CONF5_LLB)
+		c->options |= MIPS_CPU_RW_LLB;
 
 	return config5 & MIPS_CONF_M;
 }