Re: [PATCH 2/2] watchdog: generic name for i6300esb

["Daniel P. Berrangé" <berrange@redhat.com>]

On Tue, Jul 29, 2025 at 06:01:25PM +0200, Cornelia Huck wrote:
> On Thu, Jul 17 2025, Daniel P. Berrangé <berrange@redhat.com> wrote:
> 
> > On Thu, Jul 17, 2025 at 05:17:42PM +0200, Cornelia Huck wrote:
> >> On Tue, Jul 15 2025, Daniel P. Berrangé <berrange@redhat.com> wrote:
> >> 
> >> > On Tue, Jul 15, 2025 at 09:16:24AM -0700, Andrea Bolognani wrote:
> >> >> You can point them to documentation over and over again, or you can
> >> >> work to prevent the confusion/annoyance from showing up in the first
> >> >> place. Which of the two approaches is a better use of anyone's time
> >> >> is up for debate.
> >> >> 
> >> >> I for one am grateful that someone put the time in all those years
> >> >> ago and, as a result, PCI and USB controllers don't suffer from the
> >> >> problem today. Ultimately it's up to Connie though.
> >> >
> >> > The PCI/USB controller situation is not the same tradeoff though.
> >> > Those guest kernel drivers will identify and attach to these two
> >> > controllers regardless of their PCI vendor/product, via the PCI
> >> > class property. In that case changing the PCI ID and other device
> >> > metadata in QEMU is cheap as it has no negative impact on guest OS
> >> > driver compibility.
> >> >
> >> > In the case of 6300ESB though the guest driver is tied directly to
> >> > the currently used PCI device product/vendor ID.
> >> >
> >> > If we change this then we have actually created new functional
> >> > problems with guest/QEMU compatibility, in order to placate a
> >> > non-functional problem. That is not a good thing.
> >> 
> >> I don't think the suggestion was to disable the existing driver on
> >> non-Intel setups, but to add a more generic one. Still, more work to get
> >> this actually propagated into guests than doing the change in
> >> QEMU. Before I start down that route, I'd like to know whether the issue
> >> is actually big enough to make investing time there worth it.
> >
> > If we're a mmgmt app provisioning a guest, we have to choose what
> > watchdog to create - either the old one which works everywhere
> > that currently has a driver, or the new one will will work in
> > far fewer places. We'll have to wire up guest OS info about
> > watchdogs into osinfo, and then wire up all the mgmt apps to
> > query this and take action based off it. All possible, but it
> > still feels like a huge waste of time to me.
> 
> The fact that the device is something emulated and not the Intel
> hardware device is actually visible to the guest:
> 
> 00:02.0 System peripheral: Intel Corporation 6300ESB Watchdog Timer
> 	Subsystem: Red Hat, Inc. QEMU Virtual Machine
> 	Flags: fast devsel
> 	Memory at 10804000 (32-bit, non-prefetchable) [size=16]
> 	Kernel driver in use: i6300ESB timer
> 	Kernel modules: i6300esb
> 
> (lspci -v so unfortunately not immediately obvious, but still)
> 
> AFAIK the BSDs do not have a driver for this device at the moment -- and
> given what turns up when searching for i6300ESB, someone implementing a
> driver is far more likely to pick the exising PCI ID.

I see vague references (with unfortunately 404 links) to FreeBSD
supporting some ICH watchdogs, which might mean it is compatible
with the q35 built-in watchdog that all x86 q35 machines get by
default. That wouldn't help non-x86 BSD though.

> Windows would also need some dance according to Yan's mail, for unclear
> benefits.

Off-list, Richard Jones pointed to the ACPI Watchdog WADT specification
from Microsoft which appears to the most viable solution for Windows
guests - at least from x86 POV, but hopefully any future Wndows aarch64
too:

  https://download.microsoft.com/download/a/f/7/af7777e5-7dcd-4800-8a0a-b18336565f5b/HardwareWDTSpec.doc

The ACPI watchdog sounds like potentially the best bet for a working
solution across Linux and Windows, on any arch that does ACPI.... if
we can just find someone to write a QEMU driver for it....

With regards,
Daniel
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