[PATCH 3/3] arm64: cpufeature: workaround AmpereOne FEAT_BBM level 2

[Yang Shi]

FEAT_BBM level 2 is not advertised on AmpereOne because of a bug when
collapsing stage 2 mappings from smaller to larger translations.  That
doesn't impact splitting stage 1 mappings (whether stage 2 is enabled or
not), so workaround it by detecting CPUID.

Signed-off-by: Yang Shi <yang at os.amperecomputing.com>
---
 arch/arm64/include/asm/cpufeature.h | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index c7ca5f9f88bb..d9b20eb43d31 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -847,10 +847,19 @@ static inline bool bbmlv2_available(void)
 {
 	u64 mmfr2;
 	u32 bbm;
+	static const struct midr_range ampereone[] = {
+		MIDR_ALL_VERSIONS(MIDR_AMPERE1),
+		MIDR_ALL_VERSIONS(MIDR_AMPERE1A),
+		{}
+	};
 
 	mmfr2 = read_sanitised_ftr_reg(SYS_ID_AA64MMFR2_EL1);
 	bbm = cpuid_feature_extract_unsigned_field(mmfr2, ID_AA64MMFR2_EL1_BBM_SHIFT);
-	return bbm == ID_AA64MMFR2_EL1_BBM_2;
+	if ((bbm == ID_AA64MMFR2_EL1_BBM_2) ||
+	    is_midr_in_range_list(read_cpuid_id(), ampereone))
+		return true;
+
+	return false;
 }
 
 int do_emulate_mrs(struct pt_regs *regs, u32 sys_reg, u32 rt);
-- 
2.41.0