linux-kernel - Re: [PATCH 0/2] DS1374 Watchdog fixes

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Message-ID: <20170425165824.GA10024@roeck-us.net>
Date:   Tue, 25 Apr 2017 09:58:24 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Alexandre Belloni <alexandre.belloni@...e-electrons.com>
Cc:     Moritz Fischer <moritz.fischer.private@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Moritz Fischer <moritz.fischer@...us.com>,
        linux-watchdog@...r.kernel.org, wim@...ana.be,
        a.zummo@...ertech.it, rtc-linux@...glegroups.com,
        alex.williams@...com
Subject: Re: [PATCH 0/2] DS1374 Watchdog fixes

On Tue, Apr 25, 2017 at 06:32:04PM +0200, Alexandre Belloni wrote:
> On 25/04/2017 at 09:17:43 -0700, Guenter Roeck wrote:
> > On Tue, Apr 25, 2017 at 07:55:28AM -0700, Moritz Fischer wrote:
> > > Hi Guenter,
> > > 
> > > On Mon, Apr 24, 2017 at 10:03 PM, Guenter Roeck <linux@...ck-us.net> wrote:
> > > > On 04/24/2017 03:05 PM, Moritz Fischer wrote:
> > > 
> > > >> I'm very unhappy with the CONFIG_DRV_RTC_DS1374_WDT way of enabling
> > > >> the watchdog behavior and currently I'm investigating how to make
> > > >> that work via DT.
> > > >>
> > > >> Watchdog maintainers, do you have an idea on how to do that in a
> > > >> non breaking fashion?
> > > >>
> > > >
> > > > Depends on what you mean with "non breaking". Just using the normal mfd
> > > > mechanisms, ie define an mfd cell for each client driver, should work.
> > > > Do you see any problems with that ? Either case, that doesn't seem
> > > > to be a watchdog driver problem, or am I missing something ?
> > > 
> > > Well so currently watchdog behavior is selected (out of the two options alarm,
> > > or watchdog) by enabling the configuration option mentioned above.
> > > If I change this over to use a dt-based approach like dallas,ds1374-mode = <2>;
> > > to select the behavior in the mfd for example, won't that break people that
> > > relied on the old behavior? If everyone involved is ok with that, I'm happy
> > > to just add it to the binding.
> > > 
> > 
> > Sorry, I must be missing something. Looking into the driver code, my
> > understanding is that CONFIG_RTC_DRV_DS1374_WDT enables the watchdog in
> > addition to rtc functionality, not one or the other. Sure you would need
> > a different configuration option if you were to move the watchdog code into
> > drivers/watchdog, but other than that I don't really understand the problem.
> > What is the issue with, for example,
> > 
> 
> The watchdog functionality and the rtc alarm are mutually exclusive.
> 
Ah, I missed the "n" in various #ifndef statements.

I can't really comment on how to solve that; I simply don't know.
Also, even with a dt property, it still would be necessary to have
a non-DT means to configure one or the other. Making whatever solution
backward compatible also seems tricky; I don't have a solution for that
problem either.

> > > The idea was to fix what's broken currently (this patchset) and then refactor.
> > > But if you prefer I can do all in one go instead.
> > > 
> > 
> > It just seemed a waste to me to change/fix a function which is going to
> > be removed in a subsequent patch (I seem to recall that there was a fix
> > to the ioctl function).
> > 
> 
> I'd say that it depends on whether you want to backport the fixes to the
> stable kernels. Backporting the full rework is probably riskier.
> 

Good point.

Guenter