linux-kernel - Re: [PATCH 3/4] watchdog: sa11x0/pxa: get rid of get_clock_tick

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Message-ID: <0909debb-f7df-648b-95d2-23b535e5b299@roeck-us.net>
Date:   Mon, 19 Sep 2016 21:37:06 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Russell King - ARM Linux <linux@...linux.org.uk>
Cc:     Robert Jarzmik <robert.jarzmik@...e.fr>,
        Daniel Mack <daniel@...que.org>,
        Haojian Zhuang <haojian.zhuang@...il.com>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...eaurora.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Wim Van Sebroeck <wim@...ana.be>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-clk@...r.kernel.org, linux-watchdog@...r.kernel.org
Subject: Re: [PATCH 3/4] watchdog: sa11x0/pxa: get rid of get_clock_tick_rate

On 09/19/2016 03:36 PM, Russell King - ARM Linux wrote:
> On Mon, Sep 19, 2016 at 01:08:16PM -0700, Guenter Roeck wrote:
>> On Mon, Sep 19, 2016 at 09:12:14PM +0200, Robert Jarzmik wrote:
>>> The OS timer rate used for the watchdog can now be fetched from the
>>> standard clock API. This will remove the last user of
>>> get_clock_tick_rate() in both pxa and sa11x0 architectures.
>>>
>>> Signed-off-by: Robert Jarzmik <robert.jarzmik@...e.fr>
>>
>> Did you test this ? Potential problem, if built into the kernel, could be that
>> the clocks might not be ready by the time the driver is instantiated. Unless
>> this is converted to a platform driver, it won't be able to handle a
>> -EPROBE_DEFER from the clock subsystem.
>
> Really not a problem at all.  The OSTIMER0 is required for the system
> tick, and if that's not present, the kernel will be without any kind
> of time keeping, so a missing watchdog driver is the least of the
> problems.
>
> Therefore, both PXA and SA11x0 register their clocks really early to
> ensure that OSTIMER0 is available by the time_init() stage, which is
> way before driver probe time.
>

You are right. And, at least in qemu, it actually works.

Thanks,
Guenter