linux-kernel - Re: [PATCH v21 04/13] clocksource: arm_arch_timer: split arch_timer

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Message-ID: <CADyBb7utYy=VQ=hZnuecnCo1o=bXLg19ONHESUYfhBUdahoprw@mail.gmail.com>
Date:   Mon, 20 Mar 2017 21:35:12 +0800
From:   Fu Wei <fu.wei@...aro.org>
To:     Mark Rutland <mark.rutland@....com>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Marc Zyngier <marc.zyngier@....com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Sudeep Holla <sudeep.holla@....com>,
        Hanjun Guo <hanjun.guo@...aro.org>,
        linux-arm-kernel@...ts.infradead.org,
        Linaro ACPI Mailman List <linaro-acpi@...ts.linaro.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        rruigrok@...eaurora.org, "Abdulhamid, Harb" <harba@...eaurora.org>,
        Christopher Covington <cov@...eaurora.org>,
        Timur Tabi <timur@...eaurora.org>,
        G Gregory <graeme.gregory@...aro.org>,
        Al Stone <al.stone@...aro.org>, Jon Masters <jcm@...hat.com>,
        Wei Huang <wei@...hat.com>, Arnd Bergmann <arnd@...db.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>,
        Leo Duran <leo.duran@....com>,
        Wim Van Sebroeck <wim@...ana.be>,
        Guenter Roeck <linux@...ck-us.net>,
        linux-watchdog@...r.kernel.org, Tomasz Nowicki <tn@...ihalf.com>,
        Christoffer Dall <christoffer.dall@...aro.org>,
        Julien Grall <julien.grall@....com>
Subject: Re: [PATCH v21 04/13] clocksource: arm_arch_timer: split
 arch_timer_rate for different types of timer

Hi Mark,

On 18 March 2017 at 03:05, Mark Rutland <mark.rutland@....com> wrote:
> On Tue, Feb 07, 2017 at 02:50:06AM +0800, fu.wei@...aro.org wrote:
>> From: Fu Wei <fu.wei@...aro.org>
>>
>> Currently, arch_timer_rate is used to store the frequency got from per-cpu
>> arch-timer or the memory-mapped (MMIO) timers. But those values come from
>> different registers which should all be initialized by firmware.
>>
>> This patch remove arch_timer_rate, and use arch_timer_sysreg_freq and
>> arch_timer_mmio_freq instead.
>>
>> Signed-off-by: Fu Wei <fu.wei@...aro.org>
>
> Thanks for attacking this. Generally, I do think this is the right thing
> to do.
>
> However...
>
>> @@ -1070,10 +1077,9 @@ static int __init arch_timer_mem_init(struct device_node *np)
>>        * Try to determine the frequency from the device tree,
>>        * if fail, get the frequency from the CNTFRQ reg of MMIO timer.
>>        */
>> -     if (!arch_timer_rate &&
>> -         of_property_read_u32(np, "clock-frequency", &arch_timer_rate))
>> -             arch_timer_rate = arch_timer_get_mmio_freq(base);
>> -     if (!arch_timer_rate) {
>> +     if (of_property_read_u32(np, "clock-frequency", &arch_timer_mmio_freq))
>> +             arch_timer_mmio_freq = arch_timer_get_mmio_freq(base);
>> +     if (!arch_timer_mmio_freq) {
>>               pr_err(FW_BUG "frequency not available for MMIO timer.\n");
>>               ret = -EINVAL;
>>               goto out;
>
> ... unfortunately, I believe that this will break some DT platforms that
> have been (unintentionally) relying on the way currently allow the
> frequency to be probed from either the MMIO timer or the sysreg timer.
>

Ah, I 'm really not aware of this. Thanks for pointing it out.

> So while the above was my suggestion, it was not my best.
>
> For the timebeing, let's leave the single arch_timer_rate, but ensure
> that it doesn't get in the way fo the ACPI code, by making the ACPI
> probe path:
>
> * Probe the sysreg timers first, using the sysreg cntfrq().
>
> * Probe the MMIO timers second, verifying that each MMIO cntfrq matches
>   the already-probed sysreg cntfrq.
>
> ... which is what I believe you suggested previously.

OK, NP, will do this way.

>
> Thanks,
> Mark.



-- 
Best regards,

Fu Wei
Software Engineer
Red Hat