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

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Date:   Thu, 30 Nov 2017 08:15:25 -0600
From:   Govinda Tatti <govinda.tatti@...cle.com>
To:     Jan Beulich <JBeulich@...e.com>
Cc:     roger.pau@...rix.com, xen-devel@...ts.xenproject.org,
        boris.ostrovsky@...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 11/30/2017 2:27 AM, Jan Beulich wrote:
>>>> On 29.11.17 at 18:38, <govinda.tatti@...cle.com> wrote:
>>>> 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?
>> For PCIe platforms, both slot and bus reset endup resetting all connected
>> device/functions on thesecondary bus (behind the root-port or
>> downstream-port).
> According to my understanding this contradicts the comment
> ahead of pci_reset_slot(), which talks of multiple slots per bus.
> In such a setup, I can't see why resetting on slot would affect
> other slots on the same bus. At the same time the comment
> says that the slot reset may resolve to a bus one when there's
> just a single slot on the bus.
For legacy PCI/PCI-X, we can have multiple slots per bus but not with 
PCI-Express
(each link will be on a separate bus). In anycase, we need to 
walk-through other
device/functions on the same bus/slot and check their status before 
using slot/bus
reset.

Cheers
GOVINDA