Re: [Xen-devel] [PATCH] Xen/pciback: Implement PCI slot or bus reset with 'do_flr' SysFS attribute

[Govinda Tatti]

Thanks Jan for your review comments. Please see below for my comments.

On 11/7/2017 8:40 AM, Jan Beulich wrote:
> > > > On 06.11.17 at 18:48, <Govinda.Tatti@xxxxxxxxxx> wrote:
> > --- a/Documentation/ABI/testing/sysfs-driver-pciback
> > +++ b/Documentation/ABI/testing/sysfs-driver-pciback
> > @@ -11,3 +11,15 @@ Description:
> >                   #echo 00:19.0-E0:2:FF > /sys/bus/pci/drivers/pciback/quirks
> >                   will allow the guest to read and write to the configuration
> >                   register 0x0E.
> > +
> > +What:           /sys/bus/pci/drivers/pciback/do_flr
> > +Date:           Nov 2017
> > +KernelVersion:  4.15
> > +Contact:        xen-devel@xxxxxxxxxxxxxxxxxxxx
> > +Description:
> > +                An option to perform a slot or bus reset when a PCI device
> > +		is owned by Xen PCI backend. Writing a string of DDDD:BB:DD.F
> > +		will cause the pciback driver to perform a slot or bus reset
> > +		if the device supports it. It also checks to make sure that
> > +		all of the devices under the bridge are owned by Xen PCI
> > +		backend.
> Why do you name this "do_flr" when you don't even try FLR, but
> go to slot or then bus reset right away.
Yes, I agree but xen toolstack has already been modified to 
consume"do_flr" attribute. Hence, we are using the
function that matches with sysfs attribute.
> > +static int pcistub_reset_dev(struct pci_dev *dev)
> > +{
> > +	struct xen_pcibk_dev_data *dev_data;
> > +	bool slot = false, bus = false;
> > +
> > +	if (!dev)
> > +		return -EINVAL;
> > +
> > +	dev_dbg(&dev->dev, "[%s]\n", __func__);
> > +
> > +	if (!pci_probe_reset_slot(dev->slot)) {
> > +		slot = true;
> > +	} else if (!pci_probe_reset_bus(dev->bus)) {
> > +		/* We won't attempt to reset a root bridge. */
> > +		if (!pci_is_root_bus(dev->bus))
> > +			bus = true;
> > +	}
> > +
> > +	if (!bus && !slot)
> > +		return -EOPNOTSUPP;
> > +
> > +	if (!slot) {
> > +		struct pcistub_args arg = { .dev = NULL, .dcount = 0 };
> Neither of the two initializers is really needed - just {} will do.
OK.
> > +		/*
> > +		 * Make sure all devices on this bus are owned by the
> > +		 * PCI backend so that we can safely reset the whole bus.
> > +		 */
> > +		pci_walk_bus(dev->bus, pcistub_search_dev, &arg);
> > +
> > +		/* All devices under the bus should be part of pcistub! */
> > +		if (arg.dev) {
> > +			dev_err(&dev->dev, "%s device on the bus is not owned by pcistub\n",
> > +				pci_name(arg.dev));
> I think "device" is superfluous here, while "the bus" could do with
> replacing by something actually identifying the bus.
I assume you want "bus" number to be printed in above msg. If yes, will do.
> > +			return -EBUSY;
> > +		}
> > +
> > +		dev_dbg(&dev->dev, "pcistub owns %d devices on the bus\n",
> > +			arg.dcount);
> Same here for "the bus", provided this log message is useful in the
> first place.
>
> > +	}
> Aren't you missing an "else" here? Aiui in the "slot" case it may
> still be multiple devices/functions which are affected.
Good catch.  Our original code was performing same check, both for bus 
and slot case
but somehow I removed it during internal review based on some comment.

I will post revised patch later this week. Thanks.

Cheers
GOVINDA