arm64/cpufeature: Add explicit ftr_id_isar0[] for ID_ISAR0 register

ID_ISAR0[31..28] bits are RES0 in ARMv8, Reserved/UNK in ARMv7. Currently
these bits get exposed through generic_id_ftr32[] which is not desirable.
Hence define an explicit ftr_id_isar0[] array for ID_ISAR0 register where
those bits can be hidden.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org

Suggested-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/1589881254-10082-2-git-send-email-anshuman.khandual@arm.com
Signed-off-by: Will Deacon <will@kernel.org>

arch/arm64/include/asm/sysreg.h

@@ -766,6 +766,14 @@
 #define ID_ISAR4_WITHSHIFTS_SHIFT	4
 #define ID_ISAR4_UNPRIV_SHIFT		0
 
+#define ID_ISAR0_DIVIDE_SHIFT		24
+#define ID_ISAR0_DEBUG_SHIFT		20
+#define ID_ISAR0_COPROC_SHIFT		16
+#define ID_ISAR0_CMPBRANCH_SHIFT	12
+#define ID_ISAR0_BITFIELD_SHIFT		8
+#define ID_ISAR0_BITCOUNT_SHIFT		4
+#define ID_ISAR0_SWAP_SHIFT		0
+
 #define ID_ISAR5_RDM_SHIFT		24
 #define ID_ISAR5_CRC32_SHIFT		16
 #define ID_ISAR5_SHA2_SHIFT		12

arch/arm64/kernel/cpufeature.c

@@ -370,6 +370,16 @@ static const struct arm64_ftr_bits ftr_dczid[] = {
 	ARM64_FTR_END,
 };
 
+static const struct arm64_ftr_bits ftr_id_isar0[] = {
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, ID_ISAR0_DIVIDE_SHIFT, 4, 0),
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, ID_ISAR0_DEBUG_SHIFT, 4, 0),
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, ID_ISAR0_COPROC_SHIFT, 4, 0),
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, ID_ISAR0_CMPBRANCH_SHIFT, 4, 0),
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, ID_ISAR0_BITFIELD_SHIFT, 4, 0),
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, ID_ISAR0_BITCOUNT_SHIFT, 4, 0),
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, ID_ISAR0_SWAP_SHIFT, 4, 0),
+	ARM64_FTR_END,
+};
 
 static const struct arm64_ftr_bits ftr_id_isar5[] = {
 	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, ID_ISAR5_RDM_SHIFT, 4, 0),
@@ -451,7 +461,7 @@ static const struct arm64_ftr_bits ftr_zcr[] = {
  * Common ftr bits for a 32bit register with all hidden, strict
  * attributes, with 4bit feature fields and a default safe value of
  * 0. Covers the following 32bit registers:
- * id_isar[0-4], id_mmfr[1-3], id_pfr1, mvfr[0-1]
+ * id_isar[1-4], id_mmfr[1-3], id_pfr1, mvfr[0-1]
  */
 static const struct arm64_ftr_bits ftr_generic_32bits[] = {
 	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, 28, 4, 0),
@@ -497,7 +507,7 @@ static const struct __ftr_reg_entry {
 	ARM64_FTR_REG(SYS_ID_MMFR3_EL1, ftr_generic_32bits),
 
 	/* Op1 = 0, CRn = 0, CRm = 2 */
-	ARM64_FTR_REG(SYS_ID_ISAR0_EL1, ftr_generic_32bits),
+	ARM64_FTR_REG(SYS_ID_ISAR0_EL1, ftr_id_isar0),
 	ARM64_FTR_REG(SYS_ID_ISAR1_EL1, ftr_generic_32bits),
 	ARM64_FTR_REG(SYS_ID_ISAR2_EL1, ftr_generic_32bits),
 	ARM64_FTR_REG(SYS_ID_ISAR3_EL1, ftr_generic_32bits),