Re: [PATCH] xen/rpi4: implement watchdog-based reset

[Corey Minyard <cminyard@mvista.com>]

On Thu, Jun 04, 2020 at 09:15:33AM +0100, Julien Grall wrote:
> Hi,
> 
> On 04/06/2020 01:15, Corey Minyard wrote:
> > On Wed, Jun 03, 2020 at 03:31:56PM -0700, Stefano Stabellini wrote:
> > > Touching the watchdog is required to be able to reboot the board.
> > > 
> > > The implementation is based on
> > > drivers/watchdog/bcm2835_wdt.c:__bcm2835_restart in Linux.
> > 
> > Ah, I was looking at this just today, as it had been annoying me
> > greatly.  This works for me, so:
> > 
> > Tested-by: Corey Minyard <cminyard@mvista.com>
> > 
> > However, I was wondering if it might be better to handle this by failing
> > the operation in xen and passing it back to dom0 to do.  On the Pi you
> > send a firmware message to reboot, and that seems like too much to do in
> > Xen, but it would seem possible to send this back to dom0.
> I don't think this is possible in the current setup. Xen will usually
> restart the platform if Dom0 requested a clean reboot or crashed. So the
> domain wouldn't be in state to service such call.

Ok, I hadn't looked at Xen yet, I didn't know how much shutdown of dom0
happens on a reset.

> 
> > Just a
> > thought, as it might be a more general fix for other devices in the same
> > situation.
> 
> What are the devices you have in mind?

Nothing in particular, but other systems might have the same issue.  I
guess you have ACPI implemented on x86 already.  It just seemed that
Linux already has to be able to do this, and passing the buck back there
might be a more general solution.

Thanks,

-corey

> 
> Cheers,
> 
> -- 
> Julien Grall