Re: [Qemu-devel] [RFC v2 6/8] vfio_pci: fix a wrong check in vfio_pci_reset

[Alex Williamson <alex.williamson@redhat.com>]

On Wed, 2015-02-04 at 17:54 +0800, Chen Fan wrote:
> On 02/03/2015 04:16 AM, Alex Williamson wrote:
> > On Wed, 2015-01-28 at 16:37 +0800, Chen Fan wrote:
> >> when vfio device support FLR, then when device reset,
> >> we call VFIO_DEVICE_RESET ioctl to reset the device first,
> >> at kernel side, we also can see the order of reset:
> >> 3330         rc = pcie_flr(dev, probe);
> >> 3331         if (rc != -ENOTTY)
> >> 3332                 goto done;
> >> 3333
> >> 3334         rc = pci_af_flr(dev, probe);
> >> 3335         if (rc != -ENOTTY)
> >> 3336                 goto done;
> >> 3337
> >> 3338         rc = pci_pm_reset(dev, probe);
> >> 3339         if (rc != -ENOTTY)
> >> 3340                 goto done;
> >>
> >> so when vfio has FLR, reset it directly.
> >>
> >> Signed-off-by: Chen Fan <chen.fan.fnst@cn.fujitsu.com>
> >> ---
> >>   hw/vfio/pci.c | 2 +-
> >>   1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
> >> index 8c81bb3..54eb6b4 100644
> >> --- a/hw/vfio/pci.c
> >> +++ b/hw/vfio/pci.c
> >> @@ -3455,7 +3455,7 @@ static void vfio_pci_reset(DeviceState *dev)
> >>       vfio_pci_pre_reset(vdev);
> >>   
> >>       if (vdev->vbasedev.reset_works &&
> >> -        (vdev->has_flr || !vdev->has_pm_reset) &&
> >> +        vdev->has_flr &&
> >>           !ioctl(vdev->vbasedev.fd, VFIO_DEVICE_RESET)) {
> >>           trace_vfio_pci_reset_flr(vdev->vbasedev.name);
> >>           goto post_reset;
> > Does this actually fix anything?  QEMU shouldn't rely on a specific
> > behavior of the kernel.  This test is de-prioritizing a PM reset because
> > they're often non-effective.  If the device supports FLR, the second
> > part of the OR is unreached, so what's the point of this change?
> For this change, when I tested the code on my own machine.
> I found the vfio device has neither flr nor pm reset (e.g. NoSoftRst+).
> this also trigger ioctl VFIO_DEVICE_RESET, is it right?

Yes, that means that the device has a device specific reset or that it's
a singleton device on the bus and we can use the simpler path of
VFIO_DEVICE_RESET.  Thanks,

Alex