On Tue, Jun 06, 2023 at 10:06:14AM +0200, Peter Zijlstra wrote:
> 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);
This LGTM, so FWIW:
Acked-by: Mark Rutland <mark.rutland@xxxxxxx>
Longer term it'd be good to have noistr-safe forms of the MMIO accessors, but
from a quick play that's a much bigger piece of work, and I think this is fine
for now!
Thanks,
Mark.
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