linux-kernel - Re: [PATCH] clocksource/drivers/arm_arch_timer: Update sched_clock when non-boot CPUs need counter workaround

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Message-ID: <20230328135923.GB1333@willie-the-truck>
Date:   Tue, 28 Mar 2023 14:59:24 +0100
From:   Will Deacon <will@...nel.org>
To:     Marc Zyngier <maz@...nel.org>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Mark Rutland <mark.rutland@....com>,
        Daniel Lezcano <daniel.lezcano@...nel.org>,
        Thomas Gleixner <tglx@...otronix.de>, stable@...r.kernel.org,
        Yogesh Lal <quic_ylal@...cinc.com>
Subject: Re: [PATCH] clocksource/drivers/arm_arch_timer: Update sched_clock
 when non-boot CPUs need counter workaround

Hi Marc,

On Fri, Jan 13, 2023 at 11:16:48AM +0000, Marc Zyngier wrote:
> When booting on a CPU that has a countertum on the counter read,
> we use the arch_counter_get_cnt{v,p}ct_stable() backend which
> applies the workaround.
> 
> However, we don't do the same thing when an affected CPU is
> a secondary CPU, and we're stuck with the standard sched_clock()
> backend that knows nothing about the workaround.
> 
> Fix it by always indirecting sched_clock(), making arch_timer_read_counter
> a function instead of a function pointer. In turn, we update the
> pointer (now private to the driver code) when detecting a new
> workaround.
> 
> Cc: Mark Rutland <mark.rutland@....com>
> Cc: Will Deacon <will@...nel.org>
> Cc: Daniel Lezcano <daniel.lezcano@...nel.org>
> Cc: Thomas Gleixner <tglx@...otronix.de>
> Cc: stable@...r.kernel.org
> Reported-by: Yogesh Lal <quic_ylal@...cinc.com>
> Signed-off-by: Marc Zyngier <maz@...nel.org>
> Fixes: 0ea415390cd3 ("clocksource/arm_arch_timer: Use arch_timer_read_counter to access stable counters")
> Link: https://lore.kernel.org/r/ca4679a0-7f29-65f4-54b9-c575248192f1@quicinc.com
> ---
>  drivers/clocksource/arm_arch_timer.c | 56 +++++++++++++++++-----------
>  include/clocksource/arm_arch_timer.h |  2 +-
>  2 files changed, 36 insertions(+), 22 deletions(-)

I'm just going through the patch backlog and I think this thread ended
with Mark's review. Do you intend to post an updated version?

Cheers,

Will