On Fri, Sep 22, 2023 at 8:25 PM Parav Pandit <parav@xxxxxxxxxx> wrote:
>
>
> > From: Jason Gunthorpe <jgg@xxxxxxxxxx>
> > Sent: Friday, September 22, 2023 5:53 PM
>
>
> > > And what's more, using MMIO BAR0 then it can work for legacy.
> >
> > Oh? How? Our team didn't think so.
>
> It does not. It was already discussed.
> The device reset in legacy is not synchronous.
How do you know this?
> The drivers do not wait for reset to complete; it was written for the sw backend.
Do you see there's a flush after reset in the legacy driver?
static void vp_reset(struct virtio_device *vdev)
{
struct virtio_pci_device *vp_dev = to_vp_device(vdev);
/* 0 status means a reset. */
vp_legacy_set_status(&vp_dev->ldev, 0);
/* Flush out the status write, and flush in device writes,
* including MSi-X interrupts, if any. */
vp_legacy_get_status(&vp_dev->ldev);
/* Flush pending VQ/configuration callbacks. */
vp_synchronize_vectors(vdev);
}
Thanks
> Hence MMIO BAR0 is not the best option in real implementations.
>
