Re: [tip: sched/core] arm64/arch_timer: Provide noinstr sched_clock_read() functions

[Peter Zijlstra]

On Mon, Jun 05, 2023 at 07:16:18PM -0000, tip-bot2 for Peter Zijlstra wrote:
> @@ -753,14 +771,14 @@ static int arch_timer_set_next_event_phys(unsigned long evt,
>  	return 0;
>  }
>  
> -static u64 arch_counter_get_cnt_mem(struct arch_timer *t, int offset_lo)
> +static noinstr u64 arch_counter_get_cnt_mem(struct arch_timer *t, int offset_lo)
>  {
>  	u32 cnt_lo, cnt_hi, tmp_hi;
>  
>  	do {
> -		cnt_hi = readl_relaxed(t->base + offset_lo + 4);
> -		cnt_lo = readl_relaxed(t->base + offset_lo);
> -		tmp_hi = readl_relaxed(t->base + offset_lo + 4);
> +		cnt_hi = __raw_readl(t->base + offset_lo + 4);
> +		cnt_lo = __raw_readl(t->base + offset_lo);
> +		tmp_hi = __raw_readl(t->base + offset_lo + 4);
>  	} while (cnt_hi != tmp_hi);
>  
>  	return ((u64) cnt_hi << 32) | cnt_lo;

Mark noted that this looses the byteswap :/


---
Subject: arm64/arch_timer: Fix MMIO byteswap

The readl_relaxed() to __raw_readl() change meant to loose the
instrumentation, but also (inadvertently) lost the byteswap.

Fixes: 24ee7607b286 ("arm64/arch_timer: Provide noinstr sched_clock_read() functions")
Reported-by: Mark Rutland <mark.rutland@xxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
index b23d23b033cc..e733a2a1927a 100644
--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c
@@ -776,9 +776,9 @@ static noinstr u64 arch_counter_get_cnt_mem(struct arch_timer *t, int offset_lo)
 	u32 cnt_lo, cnt_hi, tmp_hi;
 
 	do {
-		cnt_hi = __raw_readl(t->base + offset_lo + 4);
-		cnt_lo = __raw_readl(t->base + offset_lo);
-		tmp_hi = __raw_readl(t->base + offset_lo + 4);
+		cnt_hi = __le32_to_cpu((__le32 __force)__raw_readl(t->base + offset_lo + 4));
+		cnt_lo = __le32_to_cpu((__le32 __force)__raw_readl(t->base + offset_lo));
+		tmp_hi = __le32_to_cpu((__le32 __force)__raw_readl(t->base + offset_lo + 4));
 	} while (cnt_hi != tmp_hi);
 
 	return ((u64) cnt_hi << 32) | cnt_lo;