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 09:47:15 +0200
From:   Alexandre Belloni <alexandre.belloni@...tlin.com>
To:     Qiang Zhao <qiang.zhao@....com>,
        Bruno Thomsen <bruno.thomsen@...il.com>
Cc:     Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        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

Hi,

On 24/09/2020 07:23:18+0000, Qiang Zhao wrote:
> > > 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
> 

I don't think there is any user upstream and it is recent engouh that we
can probably make that a positive property.

Bruno, is it ok for you? you are the only know user of the feature.


-- 
Alexandre Belloni, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com