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

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Date:   Wed, 29 Nov 2017 09:40:20 -0700
From:   "Jan Beulich" <JBeulich@...e.com>
To:     "Konrad Rzeszutek Wilk" <konrad.wilk@...cle.com>
Cc:     <xen-devel@...ts.xenproject.org>,
        "Boris Ostrovsky" <boris.ostrovsky@...cle.com>,
        "Govinda Tatti" <govinda.tatti@...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

>>> On 29.11.17 at 17:29, <konrad.wilk@...cle.com> wrote:
> On Wed, Nov 29, 2017 at 08:35:33AM -0700, Jan Beulich wrote:
>> >>> On 29.11.17 at 16:08, <govinda.tatti@...cle.com> wrote:
>> > On 11/9/2017 2:28 AM, Jan Beulich wrote:
>> >>>>> On 08.11.17 at 16:44, <govinda.tatti@...cle.com> wrote:
>> >>> 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.
>> >> That's not a valid reason imo: Right now the driver doesn't expose
>> >> such an attribute, so if the tool stack was trying to use it, it would
>> >> not do what is intended at present anyway (i.e. the code could at
>> >> best be called dead).
>> > Sure, we can consider renaming "do_flr" attribute to "pci reset" or "bus 
>> > reset".
>> > Please let me knowyour preference.
>> 
>> Well, that's more a question to Konrad as the maintainer.
>> Personally I'd prefer just "reset", as "pci" is redundant and "bus"
> 
> Can't do 'reset'.

Why?

>> doesn't cover the slot variant.
> 
> 'bus_reset' sounds lovely?

Lovely sounding or not, it may end up misleading, and even more so
if - like asked for - FLR would be tried first.

Jan