linux-kernel - Re: [PATCH v4 1/3] watchdog: aspeed: Update bootstatus handling

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Message-ID: <a0faca9a6ec7f4acdfa2f29b4ffb94b5392aea6b.camel@codeconstruct.com.au>
Date: Mon, 04 Nov 2024 10:31:55 +1030
From: Andrew Jeffery <andrew@...econstruct.com.au>
To: Patrick Williams <patrick@...cx.xyz>, Chin-Ting Kuo
	 <chin-ting_kuo@...eedtech.com>
Cc: joel@....id.au, wim@...ux-watchdog.org, linux@...ck-us.net, 
 linux-arm-kernel@...ts.infradead.org, linux-aspeed@...ts.ozlabs.org, 
 linux-kernel@...r.kernel.org, linux-watchdog@...r.kernel.org, 
 Peter.Yin@...ntatw.com, Patrick_NC_Lin@...ynn.com, Bonnie_Lo@...ynn.com, 
 DELPHINE_CHIU@...ynn.com, bmc-sw@...eedtech.com,
 chnguyen@...erecomputing.com
Subject: Re: [PATCH v4 1/3] watchdog: aspeed: Update bootstatus handling

On Fri, 2024-11-01 at 14:21 -0400, Patrick Williams wrote:
> On Fri, Nov 01, 2024 at 08:11:59PM +0800, Chin-Ting Kuo wrote:
> > The boot status mapping rule follows the latest design guide from
> > the OpenBMC shown as below.
> > https://github.com/openbmc/docs/blob/master/designs/bmc-reboot-cause-update.md#proposed-design
> > - WDIOF_EXTERN1   => system is reset by Software
> > - WDIOF_CARDRESET => system is reset by WDT SoC reset
> > - Others          => other reset events, e.g., power on reset.
> 
> I'm quite surprised that the above is relevant for a kernel driver at
> all.  Isn't "EXTERN1" a name of a real watchdog signal from your
> hardware (my recollection is that there are 2 external watchdogs).

I think you may be referring to WDTRST1 (and WDTRST2) here.

WDIOF_EXTERN1 and WDIOF_EXTERN2 have an unrelated history:

https://github.com/torvalds/linux/blame/master/include/uapi/linux/watchdog.h

>   I
> think the point of this referenced design document was that most
> users
> of BMCs have "EXTERN1" used a for software reset conditions.
> `CARDRESET` should be representing resets by the watchdog itself.

I think this is what Chin-Ting is proposing for the Aspeed driver?

> 
> The purpose of this design proposal was not to require very specific
> changes to individual watchdog drivers, but to align the userspace
> use
> with the best practices already from other watchdog drivers.  I don't
> think the kernel driver should be bending to match a particular
> userspace implementation; you should be exposing the information
> available to your hardware.

I agree with this in principle, but I'm not sure what else is meant to
be done here.

> 
> Having said that, it was known that there would need to be changes to
> the driver because some of these conditions were not adequately
> exposed
> at all.  I'm just still surprised that we're needing to reference
> that
> document as part of these changes.

I think the main question is whether an internal, graceful (userspace-
requested) reset is a reasonable use of WDIOF_EXTERN[12]. My feeling
no. I wonder whether defining a new flag (WDIOF_REBOOT?
WDIOF_GRACEFUL?) in the UAPI would be acceptable?

Andrew