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

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Thu, 4 Jun 2020, Julien Grall wrote:
> Hi,
> 
> On 04/06/2020 17:24, Stefano Stabellini wrote:
> > On Thu, 4 Jun 2020, André Przywara wrote:
> > > On 04/06/2020 09:48, Julien Grall wrote:
> > > 
> > > Hi,
> > > 
> > > > On 03/06/2020 23:31, Stefano Stabellini wrote:
> > > > > Touching the watchdog is required to be able to reboot the board.
> > > > 
> > > > In general the preferred method is PSCI. Does it mean RPI 4 doesn't
> > > > support PSCI at all?
> > > 
> > > There is mainline Trusted Firmware (TF-A) support for the RPi4 for a few
> > > months now, which includes proper PSCI support (both for SMP bringup and
> > > system reset/shutdown). At least that should work, if not, it's a bug.
> > > An EDK-2 build for RPi4 bundles TF-A automatically, but you can use TF-A
> > > without it, with or without U-Boot: It works as a drop-in replacement
> > > for armstub.bin. Instruction for building it (one line!) are here:
> > > https://git.trustedfirmware.org/TF-A/trusted-firmware-a.git/tree/docs/plat/rpi4.rst
> > > 
> > > > > 
> > > > > The implementation is based on
> > > > > drivers/watchdog/bcm2835_wdt.c:__bcm2835_restart in Linux.
> > > > 
> > > > Can you give the baseline? This would allow us to track an issue and
> > > > port them.
> > > 
> > > Given the above I don't think it's a good idea to add extra platform
> > > specific code to Xen.
> > 
> > The RPi4, at least the one I have, doesn't come with any TF, and it
> > doesn't come with PSCI in device tree. As a user, I would rather have
> > this patch (even downstream) than having to introduce TF in my build and
> > deployment just to be able to reboot.
> 
> So what are you using for the firmware? Do you boot Xen directly?

The raspberry pi comes with its own firmware/bootloader. It is possible
to boot Linux from it directly, that's how it comes configured by
default.

For Xen, I am booting uboot from the RPi bootloader first, mostly
because uboot is very convenient and adds tftp support which I use to
load Xen and Linux. (I think it would be possible to boot Xen directly
from the RPi firmware/bootloader but it would probably require some work
to get dom0 to load too.)