[RFC PATCH 2/3] arm64: cpufeature: constify arm64_ftr_regs array

[Ard Biesheuvel]

Constify the arm64_ftr_regs array, by moving the mutable arm64_ftr_reg
fields out of the array itself. This also streamlines the bsearch, since
the entire array can be covered by fewer cachelines. Moving the payload
out of the array also allows us to have special explicitly defined
struct instance in case other code needs to refer to it directly.

Note that this replaces the runtime sorting of the array with a runtime
BUG() check whether the array is sorted correctly in the code.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
---
 arch/arm64/include/asm/cpufeature.h |  1 -
 arch/arm64/kernel/cpufeature.c      | 45 +++++++++-----------
 2 files changed, 19 insertions(+), 27 deletions(-)

diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index 7c0b7cff17df..8bb4f1527b26 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -72,7 +72,6 @@ struct arm64_ftr_bits {
  * @sys_val		Safe value across the CPUs (system view)
  */
 struct arm64_ftr_reg {
-	u32				sys_id;
 	const char			*name;
 	u64				strict_mask;
 	u64				sys_val;
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index eac76cb3a206..35a17487ffb9 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -265,14 +265,17 @@ static const struct arm64_ftr_bits ftr_aa64raz[] = {
 	ARM64_FTR_END,
 };
 
-#define ARM64_FTR_REG(id, table)		\
-	{					\
-		.sys_id = id,			\
+#define ARM64_FTR_REG(id, table) {		\
+	.sys_id = id,				\
+	.reg = 	&(struct arm64_ftr_reg){	\
 		.name = #id,			\
 		.ftr_bits = &((table)[0]),	\
-	}
+	}}
 
-static struct arm64_ftr_reg arm64_ftr_regs[] = {
+static const struct __ftr_reg_entry {
+	u32			sys_id;
+	struct arm64_ftr_reg 	*reg;
+} arm64_ftr_regs[] = {
 
 	/* Op1 = 0, CRn = 0, CRm = 1 */
 	ARM64_FTR_REG(SYS_ID_PFR0_EL1, ftr_id_pfr0),
@@ -324,7 +327,7 @@ static struct arm64_ftr_reg arm64_ftr_regs[] = {
 
 static int search_cmp_ftr_reg(const void *id, const void *regp)
 {
-	return (int)(unsigned long)id - (int)((const struct arm64_ftr_reg *)regp)->sys_id;
+	return (int)(unsigned long)id - (int)((const struct __ftr_reg_entry *)regp)->sys_id;
 }
 
 /*
@@ -339,11 +342,14 @@ static int search_cmp_ftr_reg(const void *id, const void *regp)
  */
 static struct arm64_ftr_reg *get_arm64_ftr_reg(u32 sys_id)
 {
-	return bsearch((const void *)(unsigned long)sys_id,
+	const struct __ftr_reg_entry *ret;
+
+	ret = bsearch((const void *)(unsigned long)sys_id,
 			arm64_ftr_regs,
 			ARRAY_SIZE(arm64_ftr_regs),
 			sizeof(arm64_ftr_regs[0]),
 			search_cmp_ftr_reg);
+	return ret->reg;
 }
 
 static u64 arm64_ftr_set_value(const struct arm64_ftr_bits *ftrp, s64 reg,
@@ -378,27 +384,14 @@ static s64 arm64_ftr_safe_value(const struct arm64_ftr_bits *ftrp, s64 new,
 	return ret;
 }
 
-static int __init sort_cmp_ftr_regs(const void *a, const void *b)
-{
-	return ((const struct arm64_ftr_reg *)a)->sys_id -
-		 ((const struct arm64_ftr_reg *)b)->sys_id;
-}
-
-static void __init swap_ftr_regs(void *a, void *b, int size)
-{
-	struct arm64_ftr_reg tmp = *(struct arm64_ftr_reg *)a;
-	*(struct arm64_ftr_reg *)a = *(struct arm64_ftr_reg *)b;
-	*(struct arm64_ftr_reg *)b = tmp;
-}
-
 static void __init sort_ftr_regs(void)
 {
-	/* Keep the array sorted so that we can do the binary search */
-	sort(arm64_ftr_regs,
-		ARRAY_SIZE(arm64_ftr_regs),
-		sizeof(arm64_ftr_regs[0]),
-		sort_cmp_ftr_regs,
-		swap_ftr_regs);
+	int i;
+
+	/* Check that the array is sorted so that we can do the binary search */
+	for (i = 1; i < ARRAY_SIZE(arm64_ftr_regs); i++)
+		if (arm64_ftr_regs[i].sys_id < arm64_ftr_regs[i - 1].sys_id)
+			BUG();
 }
 
 /*
-- 
2.7.4