linux-kernel - RE: [Patch v2 1/3] dt-bindings: rtc: pcf2127: Add bindings for nxp,pcf2127

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Date:   Thu, 24 Sep 2020 07:23:18 +0000
From:   Qiang Zhao <qiang.zhao@....com>
To:     Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
CC:     Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Wim Van Sebroeck <wim@...ux-watchdog.org>,
        Guenter Roeck <linux@...ck-us.net>,
        "linux-watchdog@...r.kernel.org" <linux-watchdog@...r.kernel.org>,
        "a.zummo@...ertech.it" <a.zummo@...ertech.it>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "linux-rtc@...r.kernel.org" <linux-rtc@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>
Subject: RE: [Patch v2 1/3] dt-bindings: rtc: pcf2127: Add bindings for
 nxp,pcf2127

On Thu, Sep 24, 2020 at 15:05AM +0000, Uwe Kleine-König <u.kleine-koenig@...gutronix.de> wrote:

> -----Original Message-----
> From: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
> Sent: 2020年9月24日 15:05
> To: Qiang Zhao <qiang.zhao@....com>
> Cc: Alexandre Belloni <alexandre.belloni@...tlin.com>; Wim Van Sebroeck
> <wim@...ux-watchdog.org>; Guenter Roeck <linux@...ck-us.net>;
> linux-watchdog@...r.kernel.org; a.zummo@...ertech.it; robh+dt@...nel.org;
> linux-rtc@...r.kernel.org; devicetree@...r.kernel.org;
> linux-kernel@...r.kernel.org; kernel@...gutronix.de
> Subject: Re: [Patch v2 1/3] dt-bindings: rtc: pcf2127: Add bindings for
> nxp,pcf2127
> 
> Hello,
> 
> On Thu, Sep 24, 2020 at 03:20:33AM +0000, Qiang Zhao wrote:
> > On 21/09/2020 13:48:19+0800, Qiang Zhao wrote:
> >
> > > -----Original Message-----
> > > From: Alexandre Belloni <alexandre.belloni@...tlin.com>
> > > Sent: 2020年9月23日 17:45
> > > To: Qiang Zhao <qiang.zhao@....com>
> > > Cc: Wim Van Sebroeck <wim@...ux-watchdog.org>; Guenter Roeck
> > > <linux@...ck-us.net>; linux-watchdog@...r.kernel.org;
> > > a.zummo@...ertech.it; robh+dt@...nel.org; linux-rtc@...r.kernel.org;
> > > devicetree@...r.kernel.org; linux-kernel@...r.kernel.org; Uwe
> > > Kleine-König <u.kleine-koenig@...gutronix.de>
> > > Subject: Re: [Patch v2 1/3] dt-bindings: rtc: pcf2127: Add bindings
> > > for
> > > nxp,pcf2127
> > >
> > > Hi,
> > >
> > > You forgot to copy the watchdog maintainers, I think such a property
> > > should be discussed with them.
> > >
> > > Note that I'm still convinced this is not a complete solution, see:
> > > https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flo
> > > re.kern
> > >
> el.org%2Flinux-rtc%2F20200716181816.GF3428%40piout.net%2F&amp;data=
> > >
> 02%7C01%7Cqiang.zhao%40nxp.com%7Cb71f79a044b0493d6d4f08d85fa551c
> > >
> b%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0%7C1%7C637364510931174
> > >
> 355&amp;sdata=%2BOxrzB8RIuxM9Let5slhfCVmMm6PMNoERDeHC9%2Fdxng
> > > %3D&amp;reserved=0
> 
> haha
> 
> > Yes, you are right, There is not a fundamental solution.
> > However it somewhat avoid this situation at least.
> >
> > And if without this issue,
> > is it correct to register a rtc device as watchdog no matter it is used as
> watchdog on the board?
> > Every time Linux are booted up, watchdog device should be configured to the
> right one manually.
> > So the patch are useful, even though it is not for the issue.
> >
> > What should we do to really resolve this issue?
> 
> I still think we need a kernel solution here. I would expect that most assembled
> pcf2127 chips are unable to act as a watchdog (i.e. don't have the RST output
> connected to something that resets the machine).
> 
> So my favoured solution would be a positive property like:
> 
> 	has-watchdog;
> 
> or something similar. In my eyes this is definitely something we want to specify
> in the device tree because it is a relevant hardware property.
> I consider it a bug to give a watchdog device to userspace that isn't functional.
> 
> Best regards
> Uwe
 
I strongly agree with you! It should be positive property.
However, we couldn't identify which board are using pcf2127 as watchdog,
So we are unable to modify the boards' dts to correct (watchdog or not) in this patchset.

I noticed that only LS series platforms and imx6 have pcf2127 node, as far as I know, the LS platforms don't use it as watchdog,
But I am not sure about imx6

> 
> --
> Pengutronix e.K.                           | Uwe Kleine-König
> |
> Industrial Linux Solutions                 | https://www.pengutronix.de/ |
Best Regards
Qiang Zhao