linux-kernel - Re: [Linux-stm32] [PATCH v2 1/1] drivers: watchdog: stm32_iwdg: set WDOG_HW

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Message-ID: <53b2f559-3456-d378-587d-d220920e9bf7@pengutronix.de>
Date:   Fri, 22 Nov 2019 14:31:24 +0100
From:   Ahmad Fatoum <a.fatoum@...gutronix.de>
To:     Christophe ROULLIER <christophe.roullier@...com>,
        "wim@...ux-watchdog.org" <wim@...ux-watchdog.org>,
        "linux@...ck-us.net" <linux@...ck-us.net>,
        "mcoquelin.stm32@...il.com" <mcoquelin.stm32@...il.com>,
        Alexandre TORGUE <alexandre.torgue@...com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-stm32@...md-mailman.stormreply.com" 
        <linux-stm32@...md-mailman.stormreply.com>,
        "linux-watchdog@...r.kernel.org" <linux-watchdog@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>
Subject: Re: [Linux-stm32] [PATCH v2 1/1] drivers: watchdog: stm32_iwdg: set
 WDOG_HW_RUNNING at probe

Hello Christophe,

On 11/22/19 2:15 PM, Christophe ROULLIER wrote:
>> On 11/22/19 9:24 AM, Christophe Roullier wrote:
>>> +	/*
>>> +	 * In case of CONFIG_WATCHDOG_HANDLE_BOOT_ENABLED is set
>>> +	 * (Means U-Boot/bootloaders leaves the watchdog running)
>>> +	 * When we get here we should make a decision to prevent
>>> +	 * any side effects before user space daemon will take care of it.
>>> +	 * The best option, taking into consideration that there is no
>>> +	 * way to read values back from hardware, is to enforce watchdog
>>> +	 * being run with deterministic values.
>> What about the "ONF: Watchdog enable status bit" in the IWDG_SR register?

> Thanks Ahmad for your feedback, it is a mistake in our ref manual. This 
> bit is not present
> 
> in our iwdg IP, we will update our documentation accordingly.

Thanks for the info. I think it would be nice to have this information in
the driver as well, something like:

* The best option, taking into consideration that that the ONF
* watchdog status bit is non-functional, is to enforce watchdog
* being run with deterministic values.

This way it's clear that it's a deliberate choice to do it this way.

Cheers
Ahmad



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