MIPS: Add CPU shared FTLB feature detection

Some systems share FTLB RAMs or entries between sibling CPUs (ie.
hardware threads, or VP(E)s, within a core). These properties require
kernel handling in various places. As a start this patch introduces
cpu_has_shared_ftlb_ram & cpu_has_shared_ftlb_entries feature macros
which we set appropriately for I6400 & I6500 CPUs. Further patches will
make use of these macros as appropriate.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/16202/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

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

@@ -487,6 +487,47 @@
 # define cpu_has_perf		(cpu_data[0].options & MIPS_CPU_PERF)
 #endif
 
+#if defined(CONFIG_SMP) && defined(__mips_isa_rev) && (__mips_isa_rev >= 6)
+/*
+ * Some systems share FTLB RAMs between threads within a core (siblings in
+ * kernel parlance). This means that FTLB entries may become invalid at almost
+ * any point when an entry is evicted due to a sibling thread writing an entry
+ * to the shared FTLB RAM.
+ *
+ * This is only relevant to SMP systems, and the only systems that exhibit this
+ * property implement MIPSr6 or higher so we constrain support for this to
+ * kernels that will run on such systems.
+ */
+# ifndef cpu_has_shared_ftlb_ram
+#  define cpu_has_shared_ftlb_ram \
+	(current_cpu_data.options & MIPS_CPU_SHARED_FTLB_RAM)
+# endif
+
+/*
+ * Some systems take this a step further & share FTLB entries between siblings.
+ * This is implemented as TLB writes happening as usual, but if an entry
+ * written by a sibling exists in the shared FTLB for a translation which would
+ * otherwise cause a TLB refill exception then the CPU will use the entry
+ * written by its sibling rather than triggering a refill & writing a matching
+ * TLB entry for itself.
+ *
+ * This is naturally only valid if a TLB entry is known to be suitable for use
+ * on all siblings in a CPU, and so it only takes effect when MMIDs are in use
+ * rather than ASIDs or when a TLB entry is marked global.
+ */
+# ifndef cpu_has_shared_ftlb_entries
+#  define cpu_has_shared_ftlb_entries \
+	(current_cpu_data.options & MIPS_CPU_SHARED_FTLB_ENTRIES)
+# endif
+#endif /* SMP && __mips_isa_rev >= 6 */
+
+#ifndef cpu_has_shared_ftlb_ram
+# define cpu_has_shared_ftlb_ram 0
+#endif
+#ifndef cpu_has_shared_ftlb_entries
+# define cpu_has_shared_ftlb_entries 0
+#endif
+
 /*
  * Guest capabilities
  */

arch/mips/include/asm/cpu.h

@@ -418,6 +418,10 @@ enum cpu_type_enum {
 #define MIPS_CPU_GUESTID	MBIT_ULL(51)	/* CPU uses VZ ASE GuestID feature */
 #define MIPS_CPU_DRG		MBIT_ULL(52)	/* CPU has VZ Direct Root to Guest (DRG) */
 #define MIPS_CPU_UFR		MBIT_ULL(53)	/* CPU supports User mode FR switching */
+#define MIPS_CPU_SHARED_FTLB_RAM \
+				MBIT_ULL(54)	/* CPU shares FTLB RAM with another */
+#define MIPS_CPU_SHARED_FTLB_ENTRIES \
+				MBIT_ULL(55)	/* CPU shares FTLB entries with another */
 
 /*
  * CPU ASE encodings

arch/mips/kernel/cpu-probe.c

@@ -1653,6 +1653,17 @@ static inline void cpu_probe_mips(struct cpuinfo_mips *c, unsigned int cpu)
 	decode_configs(c);
 
 	spram_config();
+
+	switch (__get_cpu_type(c->cputype)) {
+	case CPU_I6500:
+		c->options |= MIPS_CPU_SHARED_FTLB_ENTRIES;
+		/* fall-through */
+	case CPU_I6400:
+		c->options |= MIPS_CPU_SHARED_FTLB_RAM;
+		/* fall-through */
+	default:
+		break;
+	}
 }
 
 static inline void cpu_probe_alchemy(struct cpuinfo_mips *c, unsigned int cpu)