Re: [PATCH v2] virtio: only reset device and restore status if needed in device resume

[Jason Wang <jasowang@xxxxxxxxxx>]

On Fri, Nov 1, 2024 at 9:54 AM <qiang4.zhang@xxxxxxxxxxxxxxx> wrote:
>
> From: Qiang Zhang <qiang4.zhang@xxxxxxxxx>
>
> Virtio core unconditionally reset and restore status for all virtio
> devices before calling restore method. This breaks some virtio drivers
> which don't need to do anything in suspend and resume because they
> just want to keep device state retained.

The challenge is how can driver know device doesn't need rest.

For example, PCI has no_soft_reset which has been done in the commit
"virtio: Add support for no-reset virtio PCI PM".

And there's a ongoing long discussion of adding suspend support in the
virtio spec, then driver know it's safe to suspend/resume without
reset.

>
> Virtio GPIO is a typical example. GPIO states should be kept unchanged
> after suspend and resume (e.g. output pins keep driving the output) and
> Virtio GPIO driver does nothing in freeze and restore methods. But the
> reset operation in virtio_device_restore breaks this.

Is this mandated by GPIO or virtio spec? If yes, let's quote the revelant part.

>
> Since some devices need reset in suspend and resume while some needn't,
> create a new helper function for the original reset and status restore
> logic so that virtio drivers can invoke it in their restore method
> if necessary.

How are those drivers classified?

>
> Signed-off-by: Qiang Zhang <qiang4.zhang@xxxxxxxxx>

Thanks