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 14:26:30 -0500
From:   Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:     Jan Beulich <JBeulich@...e.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 Wed, Nov 29, 2017 at 09:40:20AM -0700, Jan Beulich wrote:
> >>> 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?

B/c I forgot that this attribute is not per device, but on the module sub-directory:

/sys/bus/pci/drivers/pciback/do_flr

It can be indeed called 'reset'.

> 
> >> 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.

Fair enough. Reset should work then.