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

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Date:   Mon, 4 Dec 2017 10:16:31 -0600
From:   Govinda Tatti <Govinda.Tatti@...cle.COM>
To:     Jan Beulich <JBeulich@...e.com>
Cc:     Juergen Gross <jgross@...e.com>, xen-devel@...ts.xenproject.org,
        boris.ostrovsky@...cle.COM, linux-kernel@...r.kernel.org,
        roger.pau@...rix.com
Subject: Re: [Xen-devel] [PATCH V2] Xen/pciback: Implement PCI slot or bus
 reset with 'do_flr' SysFS attribute

Jan,

Do you have any further comments on the current version of this patch?. 
Otherwise, I will work on the review comments and publish next version 
of this patch later this week. Please let me know. Thanks.

Cheers
GOVINDA
On 12/1/2017 10:16 AM, Govinda Tatti wrote:
>
> On 11/30/2017 8:46 AM, Jan Beulich wrote:
>>>>> On 30.11.17 at 15:15, <govinda.tatti@...cle.com> wrote:
>>> 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).
>> Is that true even for root complex integrated end points? A
>> random system's lspci output doesn't seem to agree with what
>> you say. A typical example would be USB controllers all sitting
>> on bus 0, but having different slot numbers. You clearly won't
>> be able to ever bus-reset these, and if you checked all devices
>> on bus 0 you would then also not be able to slot-reset them.
> Here, slot reset refers to any PCIe slot that implements or supports
> hotplug feature. The slot reset ultimately invokes "pciehp_reset_slot()".
> W.r.t integrated endpoints, these can be reset either through FLR or
> secondary bus reset methods only.
>
> Cheers
> GOVINDA
>
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> Xen-devel@...ts.xenproject.org
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