linux-kernel - Re: [Xen-devel] [PATCH V2] Xen/pciback: Implement PCI slot or bus reset with 'do

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Date:   Wed, 29 Nov 2017 08:50:21 -0700
From:   "Jan Beulich" <JBeulich@...e.com>
To:     "Govinda Tatti" <govinda.tatti@...cle.com>
Cc:     <roger.pau@...rix.com>, <xen-devel@...ts.xenproject.org>,
        <boris.ostrovsky@...cle.com>, <konrad.wilk@...cle.com>,
        "Juergen Gross" <jgross@...e.com>, <linux-kernel@...r.kernel.org>
Subject: Re: [Xen-devel] [PATCH V2] Xen/pciback: Implement PCI slot or
 bus reset with 'do_flr' SysFS attribute

>>> On 29.11.17 at 16:37, <govinda.tatti@...cle.com> wrote:
> On 11/9/2017 2:49 AM, Jan Beulich wrote:
>>>>> On 09.11.17 at 00:06, <Govinda.Tatti@...cle.COM> wrote:
>>> +static int pcistub_reset_dev(struct pci_dev *dev)
>>> +{
>>> +	struct xen_pcibk_dev_data *dev_data;
>>> +	bool slot = false, bus = false;
>>> +	struct pcistub_args arg = {};
>>> +
>>> +	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)) &&
>>> +		 (!pci_is_root_bus(dev->bus)))
>>> +		bus = true;
>>> +
>>> +	if (!bus && !slot)
>>> +		return -EOPNOTSUPP;
>>> +
>>> +	/*
>>> +	 * Make sure all devices on this bus are owned by the
>>> +	 * PCI backend so that we can safely reset the whole bus.
>>> +	 */
>> Is that really the case when you mean to do a slot reset? It was for
>> a reason that I had asked about a missing "else" in v1 review,
>> rather than questioning the conditional around the logic.
> 
> In the case of bus or slot reset, our goal is to reset connected PCIe 
> fabric/card/endpoint.
> The connected card/endpoint can be multi-function device. So, same 
> walk-through and checking
> is needed irrespective of type of reset being used.

I don't follow: The scope of other devices/functions possibly
affected by a reset depends on the type of reset, doesn't it?

Jan