arm64/errata: add REVIDR handling to framework

In some cases, core variants that are affected by a certain erratum
also exist in versions that have the erratum fixed, and this fact is
recorded in a dedicated bit in system register REVIDR_EL1.

Since the architecture does not require that a certain bit retains
its meaning across different variants of the same model, each such
REVIDR bit is tightly coupled to a certain revision/variant value,
and so we need a list of revidr_mask/midr pairs to carry this
information.

So add the struct member and the associated macros and handling to
allow REVIDR fixes to be taken into account.
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>

arch/arm64/include/asm/cpufeature.h

@@ -105,6 +105,10 @@ struct arm64_cpu_capabilities {
 		struct {	/* To be used for erratum handling only */
 			u32 midr_model;
 			u32 midr_range_min, midr_range_max;
+			const struct arm64_midr_revidr {
+				u32 midr_rv;		/* revision/variant */
+				u32 revidr_mask;
+			} * const fixed_revs;
 		};
 
 		struct {	/* Feature register checking */

arch/arm64/kernel/cpu_errata.c

@@ -24,10 +24,22 @@
 static bool __maybe_unused
 is_affected_midr_range(const struct arm64_cpu_capabilities *entry, int scope)
 {
+	const struct arm64_midr_revidr *fix;
+	u32 midr = read_cpuid_id(), revidr;
+
 	WARN_ON(scope != SCOPE_LOCAL_CPU || preemptible());
-	return MIDR_IS_CPU_MODEL_RANGE(read_cpuid_id(), entry->midr_model,
+	if (!MIDR_IS_CPU_MODEL_RANGE(midr, entry->midr_model,
 				     entry->midr_range_min,
-				       entry->midr_range_max);
+				     entry->midr_range_max))
+		return false;
+
+	midr &= MIDR_REVISION_MASK | MIDR_VARIANT_MASK;
+	revidr = read_cpuid(REVIDR_EL1);
+	for (fix = entry->fixed_revs; fix && fix->revidr_mask; fix++)
+		if (midr == fix->midr_rv && (revidr & fix->revidr_mask))
+			return false;
+
+	return true;
 }
 
 static bool __maybe_unused
@@ -242,6 +254,9 @@ static int qcom_enable_link_stack_sanitization(void *data)
 	.midr_range_min = 0, \
 	.midr_range_max = (MIDR_VARIANT_MASK | MIDR_REVISION_MASK)
 
+#define MIDR_FIXED(rev, revidr_mask) \
+	.fixed_revs = (struct arm64_midr_revidr[]){{ (rev), (revidr_mask) }, {}}
+
 const struct arm64_cpu_capabilities arm64_errata[] = {
 #if	defined(CONFIG_ARM64_ERRATUM_826319) || \
 	defined(CONFIG_ARM64_ERRATUM_827319) || \