arm64: Expose DC CVAP to userspace

The ARMv8.2-DCPoP feature introduces persistent memory support to the
architecture, by defining a point of persistence in the memory
hierarchy, and a corresponding cache maintenance operation, DC CVAP.
Expose the support via HWCAP and MRS emulation.
Reviewed-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

Documentation/arm64/cpu-feature-registers.txt

@@ -179,6 +179,8 @@ infrastructure:
      | FCMA                         | [19-16] |    y    |
      |--------------------------------------------------|
      | JSCVT                        | [15-12] |    y    |
+     |--------------------------------------------------|
+     | DPB                          | [3-0]   |    y    |
      x--------------------------------------------------x
 
 Appendix I: Example

arch/arm64/include/asm/sysreg.h

@@ -329,6 +329,7 @@
 #define ID_AA64ISAR1_LRCPC_SHIFT	20
 #define ID_AA64ISAR1_FCMA_SHIFT		16
 #define ID_AA64ISAR1_JSCVT_SHIFT	12
+#define ID_AA64ISAR1_DPB_SHIFT		0
 
 /* id_aa64pfr0 */
 #define ID_AA64PFR0_GIC_SHIFT		24

arch/arm64/include/uapi/asm/hwcap.h

@@ -35,5 +35,6 @@
 #define HWCAP_JSCVT		(1 << 13)
 #define HWCAP_FCMA		(1 << 14)
 #define HWCAP_LRCPC		(1 << 15)
+#define HWCAP_DCPOP		(1 << 16)
 
 #endif /* _UAPI__ASM_HWCAP_H */

arch/arm64/kernel/cpufeature.c

@@ -120,6 +120,7 @@ static const struct arm64_ftr_bits ftr_id_aa64isar1[] = {
 	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_EXACT, ID_AA64ISAR1_LRCPC_SHIFT, 4, 0),
 	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_EXACT, ID_AA64ISAR1_FCMA_SHIFT, 4, 0),
 	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_EXACT, ID_AA64ISAR1_JSCVT_SHIFT, 4, 0),
+	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_EXACT, ID_AA64ISAR1_DPB_SHIFT, 4, 0),
 	ARM64_FTR_END,
 };
 
@@ -916,6 +917,7 @@ static const struct arm64_cpu_capabilities arm64_elf_hwcaps[] = {
 	HWCAP_CAP(SYS_ID_AA64PFR0_EL1, ID_AA64PFR0_FP_SHIFT, FTR_SIGNED, 1, CAP_HWCAP, HWCAP_FPHP),
 	HWCAP_CAP(SYS_ID_AA64PFR0_EL1, ID_AA64PFR0_ASIMD_SHIFT, FTR_SIGNED, 0, CAP_HWCAP, HWCAP_ASIMD),
 	HWCAP_CAP(SYS_ID_AA64PFR0_EL1, ID_AA64PFR0_ASIMD_SHIFT, FTR_SIGNED, 1, CAP_HWCAP, HWCAP_ASIMDHP),
+	HWCAP_CAP(SYS_ID_AA64ISAR1_EL1, ID_AA64ISAR1_DPB_SHIFT, FTR_UNSIGNED, 1, CAP_HWCAP, HWCAP_DCPOP),
 	HWCAP_CAP(SYS_ID_AA64ISAR1_EL1, ID_AA64ISAR1_JSCVT_SHIFT, FTR_UNSIGNED, 1, CAP_HWCAP, HWCAP_JSCVT),
 	HWCAP_CAP(SYS_ID_AA64ISAR1_EL1, ID_AA64ISAR1_FCMA_SHIFT, FTR_UNSIGNED, 1, CAP_HWCAP, HWCAP_FCMA),
 	HWCAP_CAP(SYS_ID_AA64ISAR1_EL1, ID_AA64ISAR1_LRCPC_SHIFT, FTR_UNSIGNED, 1, CAP_HWCAP, HWCAP_LRCPC),

arch/arm64/kernel/cpuinfo.c

@@ -68,6 +68,7 @@ static const char *const hwcap_str[] = {
 	"jscvt",
 	"fcma",
 	"lrcpc",
+	"dcpop",
 	NULL
 };