[RFC PATCH v1 2/5] arm64: cpufeature: Add an API to get level of TTRem supported by hardware

[Yanan Wang]

The ARMv8.4 architecture offers 3 levels of support when changing
block size without changing any other parameters that are listed
as requiring use of break-before-make. So get the current level
of TTRem supported by hardware and software can use corresponding
process when changing block size.

Signed-off-by: Yanan Wang <wangyanan55@xxxxxxxxxx>
---
 arch/arm64/include/asm/cpufeature.h | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index 9a555809b89c..f8ee7d30829b 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -50,6 +50,11 @@ enum ftr_type {
 #define FTR_VISIBLE	true	/* Feature visible to the user space */
 #define FTR_HIDDEN	false	/* Feature is hidden from the user */
 
+/* Supported levels of ARMv8.4 TTRem feature */
+#define TTREM_LEVEL0	0
+#define TTREM_LEVEL1	1
+#define TTREM_LEVEL2	2
+
 #define FTR_VISIBLE_IF_IS_ENABLED(config)		\
 	(IS_ENABLED(config) ? FTR_VISIBLE : FTR_HIDDEN)
 
@@ -739,6 +744,14 @@ static inline bool system_supports_tlb_range(void)
 		cpus_have_const_cap(ARM64_HAS_TLB_RANGE);
 }
 
+static inline u32 system_support_level_of_ttrem(void)
+{
+	u64 mmfr2 = read_sanitised_ftr_reg(SYS_ID_AA64MMFR2_EL1);
+
+	return cpuid_feature_extract_unsigned_field(mmfr2,
+						    ID_AA64MMFR2_BBM_SHIFT);
+}
+
 extern int do_emulate_mrs(struct pt_regs *regs, u32 sys_reg, u32 rt);
 
 static inline u32 id_aa64mmfr0_parange_to_phys_shift(int parange)
-- 
2.19.1