linux-kernel - Re: [Xen-devel] [PATCH] Xen/pciback: Implement PCI slot or bus reset with 'do

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Date:   Wed, 8 Nov 2017 09:44:48 -0600
From:   Govinda Tatti <govinda.tatti@...cle.com>
To:     Jan Beulich <JBeulich@...e.com>,
        Konrad Wilk <konrad.wilk@...cle.com>
Cc:     xen-devel@...ts.xenproject.org,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>, linux-kernel@...r.kernel.org
Subject: Re: [Xen-devel] [PATCH] Xen/pciback: Implement PCI slot or bus reset
 with 'do_flr' SysFS attribute

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@...cle.COM> 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@...ts.xenproject.org
>> +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