linux-kernel - Re: ERRATUM_858921 is broken on 5.15 kernel

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Message-ID: <ac581485-029a-f8e6-4f66-0a21f4e5bf33@quicinc.com>
Date:   Thu, 12 Jan 2023 18:17:39 +0530
From:   Yogesh Lal <quic_ylal@...cinc.com>
To:     Marc Zyngier <maz@...nel.org>
CC:     <mark.rutland@....com>, <daniel.lezcano@...aro.org>,
        <tglx@...utronix.de>, <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>
Subject: Re: ERRATUM_858921 is broken on 5.15 kernel


On 1/9/2023 4:09 PM, Marc Zyngier wrote:
> On Mon, 09 Jan 2023 06:52:20 +0000,
> Yogesh Lal <quic_ylal@...cinc.com> wrote:
>> tested it on affected h/w but looks like sched_clock is still pointing
>> to !arch_timer_counter_has_wa() function calls,
>> may be due to sched_clock_register will register once during non
>> errata impacted core booting.
> Ah, of course. We register the function itself instead of an
> indirection. Please try this on top of the previous patch.
Thanks for the patch, its working fine now.
>
> Thanks,
>
> 	M.
>
> diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
> index a7cf0a2c86d3..8232c86b9e7c 100644
> --- a/drivers/clocksource/arm_arch_timer.c
> +++ b/drivers/clocksource/arm_arch_timer.c
> @@ -217,7 +217,12 @@ static notrace u64 arch_counter_get_cntvct(void)
>    * to exist on arm64. arm doesn't use this before DT is probed so even
>    * if we don't have the cp15 accessors we won't have a problem.
>    */
> -u64 (*arch_timer_read_counter)(void) __ro_after_init = arch_counter_get_cntvct;
> +static u64 (*__arch_timer_read_counter)(void) __ro_after_init = arch_counter_get_cntvct;
> +
> +u64 arch_timer_read_counter(void)
> +{
> +	return __arch_timer_read_counter();
> +}
>   EXPORT_SYMBOL_GPL(arch_timer_read_counter);
>   
>   static u64 arch_counter_read(struct clocksource *cs)
> @@ -595,7 +600,7 @@ void arch_timer_enable_workaround(const struct arch_timer_erratum_workaround *wa
>   
>   	if (wa->read_cntvct_el0 || wa->read_cntpct_el0) {
>   		atomic_set(&timer_unstable_counter_workaround_in_use, 1);
> -		arch_timer_read_counter = arch_counter_get_read_fn();
> +		__arch_timer_read_counter = arch_counter_get_read_fn();
>   	}
>   
>   	/*
> @@ -1103,10 +1108,10 @@ static void __init arch_counter_register(unsigned type)
>   
>   	/* Register the CP15 based counter if we have one */
>   	if (type & ARCH_TIMER_TYPE_CP15) {
> -		arch_timer_read_counter = arch_counter_get_read_fn();
> +		__arch_timer_read_counter = arch_counter_get_read_fn();
>   		clocksource_counter.vdso_clock_mode = vdso_default;
>   	} else {
> -		arch_timer_read_counter = arch_counter_get_cntvct_mem;
> +		__arch_timer_read_counter = arch_counter_get_cntvct_mem;
>   	}
>   
>   	width = arch_counter_get_width();
> diff --git a/include/clocksource/arm_arch_timer.h b/include/clocksource/arm_arch_timer.h
> index e3c3816d19ba..3ac297a756e8 100644
> --- a/include/clocksource/arm_arch_timer.h
> +++ b/include/clocksource/arm_arch_timer.h
> @@ -89,7 +89,7 @@ struct arch_timer_mem {
>   #ifdef CONFIG_ARM_ARCH_TIMER
>   
>   extern u32 arch_timer_get_rate(void);
> -extern u64 (*arch_timer_read_counter)(void);
> +extern u64 arch_timer_read_counter(void);
>   extern struct arch_timer_kvm_info *arch_timer_get_kvm_info(void);
>   extern bool arch_timer_evtstrm_available(void);
>   
>