arm64/sme: Expose SMIDR through sysfs

We currently expose MIDR and REVID to userspace through sysfs to enable it
to make decisions based on the specific implementation. Since SME supports
implementations where streaming mode is provided by a separate hardware
unit called a SMCU it provides a similar ID register SMIDR. Expose it to
userspace via sysfs when the system supports SME along with the other ID
registers.

Since we disable the SME priority mapping feature if it is supported by
hardware we currently mask out the SMPS bit which reports that it is
supported.

Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20220607132857.1358361-1-broonie@kernel.org
Signed-off-by: Will Deacon <will@kernel.org>

1 files changed, 22 insertions, 1 deletions

diff --git a/arch/arm64/kernel/cpuinfo.c b/arch/arm64/kernel/cpuinfo.c
index 8eff0a34ffd4..7f06df59df2b 100644
--- a/arch/arm64/kernel/cpuinfo.c
+++ b/arch/arm64/kernel/cpuinfo.c
@@ -267,6 +267,7 @@ static struct kobj_type cpuregs_kobj_type = {
 
 CPUREGS_ATTR_RO(midr_el1, midr);
 CPUREGS_ATTR_RO(revidr_el1, revidr);
+CPUREGS_ATTR_RO(smidr_el1, smidr);
 
 static struct attribute *cpuregs_id_attrs[] = {
 	&cpuregs_attr_midr_el1.attr,
@@ -279,6 +280,16 @@ static const struct attribute_group cpuregs_attr_group = {
 	.name = "identification"
 };
 
+static struct attribute *sme_cpuregs_id_attrs[] = {
+	&cpuregs_attr_smidr_el1.attr,
+	NULL
+};
+
+static const struct attribute_group sme_cpuregs_attr_group = {
+	.attrs = sme_cpuregs_id_attrs,
+	.name = "identification"
+};
+
 static int cpuid_cpu_online(unsigned int cpu)
 {
 	int rc;
@@ -296,6 +307,8 @@ static int cpuid_cpu_online(unsigned int cpu)
 	rc = sysfs_create_group(&info->kobj, &cpuregs_attr_group);
 	if (rc)
 		kobject_del(&info->kobj);
+	if (system_supports_sme())
+		rc = sysfs_merge_group(&info->kobj, &sme_cpuregs_attr_group);
 out:
 	return rc;
 }
@@ -423,9 +436,17 @@ static void __cpuinfo_store_cpu(struct cpuinfo_arm64 *info)
 		info->reg_zcr = read_zcr_features();
 
 	if (IS_ENABLED(CONFIG_ARM64_SME) &&
-	    id_aa64pfr1_sme(info->reg_id_aa64pfr1))
+	    id_aa64pfr1_sme(info->reg_id_aa64pfr1)) {
 		info->reg_smcr = read_smcr_features();
 
+		/*
+		 * We mask out SMPS since even if the hardware
+		 * supports priorities the kernel does not at present
+		 * and we block access to them.
+		 */
+		info->reg_smidr = read_cpuid(SMIDR_EL1) & ~SMIDR_EL1_SMPS;
+	}
+
 	cpuinfo_detect_icache_policy(info);
 }