linux-kernel - Re: [PATCH v2 27/45] mfd: ntxec: Use devm_register_power

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Date:   Sun, 7 Nov 2021 20:42:33 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Guenter Roeck <linux@...ck-us.net>,
        Jonathan Neuschäfer <j.neuschaefer@....net>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Lee Jones <lee.jones@...aro.org>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Mark Brown <broonie@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Russell King <linux@...linux.org.uk>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Guo Ren <guoren@...nel.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
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Subject: Re: [PATCH v2 27/45] mfd: ntxec: Use devm_register_power_handler()

07.11.2021 20:32, Guenter Roeck пишет:
> On 11/7/21 9:16 AM, Dmitry Osipenko wrote:
>> 07.11.2021 20:08, Guenter Roeck пишет:
>>> On 11/7/21 8:53 AM, Dmitry Osipenko wrote:
>>>> 06.11.2021 23:54, Jonathan Neuschäfer пишет:
>>>>> Hi,
>>>>>
>>>>> On Thu, Oct 28, 2021 at 12:16:57AM +0300, Dmitry Osipenko wrote:
>>>>>> Use devm_register_power_handler() that replaces global pm_power_off
>>>>>> variable and allows to register multiple power-off handlers. It also
>>>>>> provides restart-handler support, i.e. all in one API.
>>>>>>
>>>>>> Signed-off-by: Dmitry Osipenko <digetx@...il.com>
>>>>>> ---
>>>>>
>>>>> When I boot with (most of) this patchset applied, I get the warning at
>>>>> kernel/reboot.c:187:
>>>>>
>>>>>      /*
>>>>>       * Handler must have unique priority. Otherwise call order is
>>>>>       * determined by registration order, which is unreliable.
>>>>>       */
>>>>>      WARN_ON(!atomic_notifier_has_unique_priority(&restart_handler_list,
>>>>>
>>>>> nb));
>>>>>
>>>>> As the NTXEC driver doesn't specify a priority, I think this is an
>>>>> issue
>>>>> to be fixed elsewhere.
>>>>>
>>>>> Other than that, it works and looks good, as far as I can tell.
>>>>>
>>>>>
>>>>> For this patch:
>>>>>
>>>>> Reviewed-by: Jonathan Neuschäfer <j.neuschaefer@....net>
>>>>> Tested-by: Jonathan Neuschäfer <j.neuschaefer@....net>
>>>>
>>>> Thank you. You have conflicting restart handlers, apparently NTXEC
>>>> driver should have higher priority than the watchdog driver. It should
>>>> be a common problem for the watchdog drivers, I will lower watchdog's
>>>> default priority to fix it.
>>>>
>>>
>>> The watchdog subsystem already uses "0" as default priority, which was
>>> intended as priority of last resort for restart handlers. I do not see
>>> a reason to change that.
>>
>> Right, I meant that watchdog drivers which use restart handler set the
>> level to the default 128 [1]. Although, maybe it's a problem only for
>> i.MX drivers in practice, I'll take a closer look at the other drivers.
>>
> 
> They don't have to do that. The default is priority 0. It is the decision
> of the driver author to set the watchdog's restart priority. So it is wrong
> to claim that this would be "a common problem for the watchdog drivers",
> because it isn't. Presumably there was a reason for the driver author
> to select the default priority of 128. If there is a platform which has
> a better means to restart the system, it should select a priority of
> 129 or higher instead of affecting _all_ platforms using the imx watchdog
> to reset the system.
> 
> Sure, you can negotiate that with the driver author, but the default should
> really be to change the priority for less affected platforms.

Yes, looks like there is no common problem for watchdog drivers.
Initially I was recalling that watchdog core uses 128 by default and
typed the message without verifying it. I see now that it's incorrect,
my bad.

EC drivers tend to use higher priority in general. Jonathan, could you
please confirm that NTXEC driver is a more preferable restart method
than the watchdog?