linux-kernel - Re: [PATCH 03/13] RTC: ds1307: Add DS1341 specific power-saving options

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Date:	Tue, 12 Jul 2016 09:21:14 -0700
From:	Andrey Smirnov <andrew.smirnov@...il.com>
To:	Alexandre Belloni <alexandre.belloni@...e-electrons.com>
Cc:	Rob Herring <robh@...nel.org>, rtc-linux@...glegroups.com,
	Alessandro Zummo <a.zummo@...ertech.it>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 03/13] RTC: ds1307: Add DS1341 specific power-saving options

On Tue, Jun 21, 2016 at 7:34 PM, Andrey Smirnov
<andrew.smirnov@...il.com> wrote:
> On Tue, Jun 21, 2016 at 2:07 PM, Alexandre Belloni
> <alexandre.belloni@...e-electrons.com> wrote:
>> On 21/06/2016 at 15:49:04 -0500, Rob Herring wrote :
>>> So wouldn't you want to set one mode while running and the lower power
>>> mode while suspended? I'm trying to understand the frequency of changing
>>> this. If it is always one setting for a board, then yes it belongs in
>>> DT. If it is a user decision, then it probably shouldn't be in DT.
>>>
>>> Seeing as these are reused, I've probably already had this discussion...
>>>
>>
>> I would agree with Rob here. It may be better to provide a sysfs
>> interface to configure that particular behavior.
>
> I don't see any value in doing that, could you give me a realistic
> example of a scenario in which a user would want to spend some of
> uptime with RTC oscillator fault detection/glitch filtering disabled
> and then enable it?
>
>> This is usually ok because the use case is:
>>  - the RTC is not configured, time has never been set
>>  - time is set for the first time
>>  - the user can set the oscillator mode/detection/...
>
> Unfortunately exposing that feature using sysfs gives you a leaky
> abstraction and your userspace instead of using a generic RTC starts
> using DS1341 RTC. So to accommodate for that a user would have to:
>
> a) Write + integrate a userspace tool to set the mode (which IMHO is
> decided upon once and doesn't change)
> b) If a board design is new and there's a chance of moving this chip
> to a different I2C bus, the code above would have to account for that
> and not hardcore sysfs path
> c) If board's BSP is intended to be used in multiple generations of a
> product, not all of which would use DS1341, it would be necessary to
> accommodate for that by either more code in the tool or an additional
> BSP build configuration variant
>
>>  - on subsequent reboots, the mode is kept alongside the time and date
>>
>
> This assumes that your bootloader leaves those mode bits alone.
>
>> I would advise against trying to set a mode automatically in the driver
>> because you may have unexpected power cuts and it may then let the RTC
>> consume more power than what you really want.
>>
>
> I fell like I am not understanding you correctly.  Why would moving
> configuration decision logic into userspace improve the situation in
> case of unexpected power loss?
>
> Andrey


Alexandre, what's the status of this discussion/patchset? Would it be
more acceptable if I dropped all of the refactoring and just kept the
code adding new feature + DT binding for it? I am more than happy to
drop all but essential parts of the patches if that would allow us to
make progress.

Thank you,
Andrey