[PATCH] arm64: arch_timer: reuse arch_timer_read_cnt{p,v}ct_el0() helpers

[PATCH] arm64: arch_timer: reuse arch_timer_read_cnt{p,v}ct_el0() helpers

[Breno Leitao]

__arch_counter_get_cntpct() and __arch_counter_get_cntvct() open-code
the same ECV-aware ALTERNATIVE block that arch_timer_read_cntpct_el0()
and arch_timer_read_cntvct_el0() already provide in the same header.
The two pairs are byte-for-byte identical except for the trailing
arch_counter_enforce_ordering() the __arch_counter_get_* variants add.

Replace the duplicated inline assembly in __arch_counter_get_cntpct()
and __arch_counter_get_cntvct() with calls to the corresponding helpers.
This mirrors commit 00b39d150986 ("arm64: vdso: Use
__arch_counter_get_cntvct()"), which removed similar duplication from
the vDSO, and keeps the system-counter read sequence in a single place,
reducing assembly code in the kernell

No functional change: the resulting inline assembly, alternatives, and
clobbers are unchanged; only the source-level expression of the read
moves into the existing helper.

Verified by rebuilding the consumers of these helpers before and after
the change and comparing the resulting disassembly:

  - arch/arm64/kernel/vdso/vdso.so (final linked vDSO):
      bit-identical (same sha256 across rebuilds)
  - arch/arm64/kernel/vdso/vgettimeofday.o:    identical disassembly
  - arch/arm64/lib/delay.o:                    identical disassembly
  - drivers/clocksource/arm_arch_timer.o:      same 50 functions with
      byte-identical instruction streams; only difference is function
      ordering inside .text and NOP padding, with no opcodes added or
      removed.

Signed-off-by: Breno Leitao <leitao@debian.org>
---
 arch/arm64/include/asm/arch_timer.h | 12 ++----------
 1 file changed, 2 insertions(+), 10 deletions(-)

diff --git a/arch/arm64/include/asm/arch_timer.h b/arch/arm64/include/asm/arch_timer.h
index f5794d50f51d..6717209df05b 100644
--- a/arch/arm64/include/asm/arch_timer.h
+++ b/arch/arm64/include/asm/arch_timer.h
@@ -178,12 +178,8 @@ static __always_inline u64 __arch_counter_get_cntpct_stable(void)
 
 static __always_inline u64 __arch_counter_get_cntpct(void)
 {
-	u64 cnt;
+	u64 cnt = arch_timer_read_cntpct_el0();
 
-	asm volatile(ALTERNATIVE("isb\n mrs %0, cntpct_el0",
-				 "nop\n" __mrs_s("%0", SYS_CNTPCTSS_EL0),
-				 ARM64_HAS_ECV)
-		     : "=r" (cnt));
 	arch_counter_enforce_ordering(cnt);
 	return cnt;
 }
@@ -199,12 +195,8 @@ static __always_inline u64 __arch_counter_get_cntvct_stable(void)
 
 static __always_inline u64 __arch_counter_get_cntvct(void)
 {
-	u64 cnt;
+	u64 cnt = arch_timer_read_cntvct_el0();
 
-	asm volatile(ALTERNATIVE("isb\n mrs %0, cntvct_el0",
-				 "nop\n" __mrs_s("%0", SYS_CNTVCTSS_EL0),
-				 ARM64_HAS_ECV)
-		     : "=r" (cnt));
 	arch_counter_enforce_ordering(cnt);
 	return cnt;
 }

---
base-commit: 9f84f9898cf191aa251268547ceef03abb8d1edd
change-id: 20260523-arch64_fix-6416179b7173

Best regards,
--  
Breno Leitao <leitao@debian.org>

Re: [PATCH] arm64: arch_timer: reuse arch_timer_read_cnt{p,v}ct_el0() helpers

[Will Deacon]

On Sat, 23 May 2026 12:59:26 -0400, Breno Leitao wrote:
> __arch_counter_get_cntpct() and __arch_counter_get_cntvct() open-code
> the same ECV-aware ALTERNATIVE block that arch_timer_read_cntpct_el0()
> and arch_timer_read_cntvct_el0() already provide in the same header.
> The two pairs are byte-for-byte identical except for the trailing
> arch_counter_enforce_ordering() the __arch_counter_get_* variants add.
> 
> Replace the duplicated inline assembly in __arch_counter_get_cntpct()
> and __arch_counter_get_cntvct() with calls to the corresponding helpers.
> This mirrors commit 00b39d150986 ("arm64: vdso: Use
> __arch_counter_get_cntvct()"), which removed similar duplication from
> the vDSO, and keeps the system-counter read sequence in a single place,
> reducing assembly code in the kernell
> 
> [...]

Applied to arm64 (for-next/misc), thanks!

[1/1] arm64: arch_timer: reuse arch_timer_read_cnt{p,v}ct_el0() helpers
      https://git.kernel.org/arm64/c/11c33ffb3a4e

Cheers,
-- 
Will

https://fixes.arm64.dev
https://next.arm64.dev
https://will.arm64.dev