Re: [Qemu-devel] [PATCH] vfio: fix duplicate function call

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

On Fri, 14 Oct 2016 19:16:59 +0800
Cao jin <caoj.fnst@cn.fujitsu.com> wrote:

> When vfio device is reset(encounter FLR, or bus reset), if need to do
> bus reset(vfio_pci_hot_reset_one is called), vfio_pci_pre_reset &
> vfio_pci_post_reset will be called twice.
> 
> Signed-off-by: Cao jin <caoj.fnst@cn.fujitsu.com>
> ---
> Also has a little question on vfio_pci_reset. it will be called when encounter
> bus reset, or FLR. The reset method's priority in this function now is:
> 
>     1. If has "device specific reset function", then do it
>     2. If has FLR, then do it.
>     3. If it can do bus reset(only 1 affected device), then do it
>     4. If has pm_reset, then do it
> 
> The question is: why pm reset has low priority than bus reset(if it does
> can do a bus reset)? why bus reset is not the last choice? In PCI driver
> of kernel, pls see __pci_dev_reset, we can see, if device support pm reset,
> it won't do bus reset.

The PCI spec doesn't really define what sort of reset is done with a PM
reset.  My thinking was that if a device advertises an FLR capability
then the hardware has made a concerted effort to have a per function
reset mechanism available.  NoSoftRst- is not terribly common and it's
not entirely clear to me that the hardware has made a conscious effort
to provide this for the purposes of per function reset mechanism.
Therefore I've opt'd to prioritize a bus reset over a PM reset.
 
>  hw/vfio/pci.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
> index cce3024..ca4d1c1 100644
> --- a/hw/vfio/pci.c
> +++ b/hw/vfio/pci.c
> @@ -1930,7 +1930,9 @@ static int vfio_pci_hot_reset(VFIOPCIDevice *vdev, bool single)
>  
>      trace_vfio_pci_hot_reset(vdev->vbasedev.name, single ? "one" : "multi");
>  
> -    vfio_pci_pre_reset(vdev);
> +    if (!single) {
> +        vfio_pci_pre_reset(vdev);
> +    }
>      vdev->vbasedev.needs_reset = false;
>  
>      info = g_malloc0(sizeof(*info));
> @@ -2088,7 +2090,9 @@ out:
>          }
>      }
>  out_single:
> -    vfio_pci_post_reset(vdev);
> +    if (!single) {
> +        vfio_pci_post_reset(vdev);
> +    }
>      g_free(info);
>  
>      return ret;

Looks ok to me, I'll queue it.  Thanks,

Alex