Re: [PATCH 0/4] drm/xe: Implement device shutdown to make kexec work.

[Rodrigo Vivi <rodrigo.vivi@intel.com>]

On Fri, Sep 06, 2024 at 11:52:43AM +0200, Maarten Lankhorst wrote:
>
>
> Den 2024-09-05 kl. 19:34, skrev Jani Nikula:
> > On Thu, 05 Sep 2024, Maarten Lankhorst <maarten.lankhorst@linux.intel.com> wrote:
> >> Testcase:
> >> kexec --reuse-cmdline --initrd=initrd.img -f vmlinuz
> >>
> >> Because we don't shut down xe correctly, we cannot reload xe afterwards.
> >> Implement device shutdown by performing a FLR, then we can load the device
> >> cleanly again afterwards.
> >
> > Maybe a silly question, but what's FLR?
> Function level reset. It resets all the resources on the device, so display, all gt's etc are all turned off.
> It's far faster than resetting each component separately. And it even works if display is the cause off a panic
> since no locks are qrequired.

Just to avoid confusion, I like to call this one as driver-initiated-FLR.
It is a feature introduced back in gen11, I believe, where the driver can use
MMIO to request the reset of many IP blocks including GT, SGUnit, Display, etc.

But it is not the same as the full PCI Function Level Reset as some components
won't get reset nor have the memory wiped out.

The only way to get the PCI FLR is doing echo 1 to device/reset:
echo 1 /sys/class/drm/card1/device/reset

On my scripts when I want a full clean start I have something like this:

echo -n "0000:00:02.0" | sudo tee /sys/bus/pci/drivers/i915/unbind
echo -n 1 | sudo tee /sys/bus/pci/devices/0000\:00\:02.0/reset
echo -n "0000:00:02.0" | sudo tee /sys/bus/pci/drivers/i915/bind

Hopefully on Xe will be able to support the echo 1 > device/reset
without having to unbind and reprobe:

https://lore.kernel.org/intel-xe/20240422065756.294679-1-aravind.iddamsetty@linux.intel.com/

Cc: Aravind Iddamsetty <aravind.iddamsetty@linux.intel.com>

>
> Cheers,
> ~Maarten