linux-kernel - Re: [PATCH 2/2] watchdog: Add Apple SoC watchdog driver

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Date:   Thu, 02 Dec 2021 12:05:41 +0100
From:   "Sven Peter" <sven@...npeter.dev>
To:     "Hector Martin" <marcan@...can.st>,
        "Alyssa Rosenzweig" <alyssa@...enzweig.io>
Cc:     "Wim Van Sebroeck" <wim@...ux-watchdog.org>,
        "Guenter Roeck" <linux@...ck-us.net>,
        "Rob Herring" <robh+dt@...nel.org>,
        "Mark Kettenis" <mark.kettenis@...all.nl>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-watchdog@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 2/2] watchdog: Add Apple SoC watchdog driver



On Thu, Dec 2, 2021, at 06:14, Hector Martin wrote:
> On 14/11/2021 22.18, Alyssa Rosenzweig wrote:
>>>>> + * This HW block has three separate watchdogs. WD0 resets the machine
>>>>> + * to recovery mode and is not very useful for us. WD1 and WD2 trigger a normal
>>>>> + * machine reset. WD0 additionally supports a configurable interrupt.
>>>>
>>>> Do we have any idea what the difference between WD1 and WD2 is?
>>>
>>> I've never seen macOS write to WD2 when running in our hypervisor and only
>>> found that one when I was looking at the rest of the MMIO region.
>>> >From what I can tell it works exactly like WD1.
>> 
>> Makes sense, thanks.
>> 
>
> Are any of these watchdogs active when we boot, and are we leaving them 
> like that? I'm pretty sure at least some of the coprocessors have their 
> own watchdog (SMC...), which might be one of these. We should make sure 
> we don't clobber that.

That's what I thought at first as well but they are all disabled except for
WD1 which we disable in m1n1.
I don't touch WD0 or WD2 in this driver anyway and v2 also checks if WD1 is
running (because it might've been started by u-boot) and makes sure the
watchdog core is aware and keeps pinging it.


Sven