linux-kernel - Re: [PATCH 2/7] watchdog/sbsa: Use arch_timer_read_counter instead of arch_counter_get

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Message-ID: <49c5a522-585f-4c05-6acf-0930a3b0670b@arm.com>
Date:   Tue, 9 Apr 2019 08:43:01 +0100
From:   Marc Zyngier <marc.zyngier@....com>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Russell King <linux@....linux.org.uk>,
        Will Deacon <will.deacon@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Mark Rutland <mark.rutland@....com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Wim Van Sebroeck <wim@...ux-watchdog.org>,
        Valentin Schneider <valentin.schneider@....com>
Subject: Re: [PATCH 2/7] watchdog/sbsa: Use arch_timer_read_counter instead of
 arch_counter_get_cntvct

On 08/04/2019 19:07, Guenter Roeck wrote:
> On Mon, Apr 08, 2019 at 04:49:02PM +0100, Marc Zyngier wrote:
>> Only arch_timer_read_counter will guarantee that workarounds are
>> applied. So let's use this one instead of arch_counter_get_cntvct.
>>
>> Signed-off-by: Marc Zyngier <marc.zyngier@....com>
> 
> Reviewed-by: Guenter Roeck <linux@...ck-us.net>
> 
> ... assuming/hoping that those counters are actually the same.

There is only a single counter. It is just that in a number of cases,
the HW will return nonsensical values, which is a bit annoying if you
end-up feeding this garbage to a watchdog.

arch_timer_read_counter() guarantees that *if* there is a workaround for
the timer, it gets applied. arch_counter_get_cntvct() only returns the
raw value, with potential side effects.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...