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

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Message-ID: <20200924070456.rovgp6n5q25s53vc@pengutronix.de>
Date:   Thu, 24 Sep 2020 09:04:56 +0200
From:   Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
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" <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
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%2Flore.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

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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