Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [PATCH 7/7] clocksource/arm_arch_timer: Use
 arch_timer_read_counter to access stable counters
To:     Valentin Schneider <valentin.schneider@arm.com>,
        Marc Zyngier <marc.zyngier@arm.com>,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org
Cc:     Russell King <linux@arm.linux.org.uk>,
        Will Deacon <will.deacon@arm.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Wim Van Sebroeck <wim@linux-watchdog.org>,
        Guenter Roeck <linux@roeck-us.net>
References: <20190408154907.223536-1-marc.zyngier@arm.com>
 <20190408154907.223536-8-marc.zyngier@arm.com>
 <2a60a031-1eab-2d5e-89ff-b5d516545eeb@linaro.org>
 <bbe9b8c1-132f-bbfa-e3d0-ad10c4165ad7@arm.com>
 <cef220b8-f46d-0653-8249-a9d48b2efc48@arm.com>
From:   Daniel Lezcano <daniel.lezcano@linaro.org>
Message-ID: <c8449908-1f8a-a10e-bfce-95bd7415e523@linaro.org>
Date:   Fri, 3 May 2019 22:32:24 +0200
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101
 Thunderbird/60.6.1
MIME-Version: 1.0
In-Reply-To: <cef220b8-f46d-0653-8249-a9d48b2efc48@arm.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


Hi Valentin,

On 30/04/2019 17:39, Valentin Schneider wrote:
> Hi,
> 
> On 30/04/2019 16:27, Marc Zyngier wrote:
> [...]
>>>> @@ -372,6 +392,7 @@ static u32 notrace sun50i_a64_read_cntv_tval_el0(void)
>>>>  DEFINE_PER_CPU(const struct arch_timer_erratum_workaround *, timer_unstable_counter_workaround);
>>>>  EXPORT_SYMBOL_GPL(timer_unstable_counter_workaround);
>>>>  
>>>> +static atomic_t timer_unstable_counter_workaround_in_use = ATOMIC_INIT(0);
>>>
>>> Wouldn't make sense to READ_ONCE / WRITE_ONCE instead of using an atomic?
>>
>> I don't think *_ONCE says anything about the atomicity of the access. It
>> only instruct the compiler that this should only be accessed once, and
>> not reloaded/rewritten.
> 
> FWIW 7bd3e239d6c6 ("locking: Remove atomicy checks from {READ,WRITE}_ONCE")
> points this out.

Interesting, thanks for the pointer.

  -- Daniel


-- 
 <http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs

Follow Linaro:  <http://www.facebook.com/pages/Linaro> Facebook |
<http://twitter.com/#!/linaroorg> Twitter |
<http://www.linaro.org/linaro-blog/> Blog