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 17:26:47 -0600
From:   Govinda Tatti <govinda.tatti@...cle.com>
To:     Pasi Kärkkäinen <pasik@....fi>
Cc:     Juergen Gross <jgross@...e.com>,
        Konrad Wilk <konrad.wilk@...cle.com>,
        linux-kernel@...r.kernel.org, Jan Beulich <JBeulich@...e.com>,
        xen-devel@...ts.xenproject.org,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>
Subject: Re: [Xen-devel] [PATCH] Xen/pciback: Implement PCI slot or bus reset
 with 'do_flr' SysFS attribute

Thanks Pasi for your response. Please see below for my comments.

On 11/8/2017 11:38 AM, Pasi Kärkkäinen wrote:
> Hi,
>
> On Wed, Nov 08, 2017 at 09:44:48AM -0600, Govinda Tatti wrote:
>> 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.
>>
> Hmm.. I remember some discussion from ages ago related to this.
>
> Back then it was suggested to "emulate" the flr capability (by doing slot or bus reset) for devices which don't have *native* flr available? So is this patch perhaps related to that?
I don't think so but either Konrad or someone can comment on it.
>
> If the PCI device in question has native flr capability, then native flr is used, right ?
Yes.
> I guess I should read the full patch..
Please check it and let us know your comments.

Cheers
GOVINDA