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

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Wed, Nov 29, 2017 at 08:35:33AM -0700, Jan Beulich wrote:
> >>> On 29.11.17 at 16:08, <govinda.tatti@xxxxxxxxxx> wrote:
> > On 11/9/2017 2:28 AM, Jan Beulich wrote:
> >>>>> On 08.11.17 at 16:44, <govinda.tatti@xxxxxxxxxx> wrote:
> >>> On 11/7/2017 8:40 AM, Jan Beulich wrote:
> >>>>>>> On 06.11.17 at 18:48, <Govinda.Tatti@xxxxxxxxxx> 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@xxxxxxxxxxxxxxxxxxxx 
> >>>>> +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'.
> doesn't cover the slot variant.

'bus_reset' sounds lovely?
> 
> >> Furthermore, contrary to what you claim in
> >> your reply to Pasi, I can't see where you try an actual FLR first -
> >> you go straight to pci_probe_reset_{slot,bus}(). If you actually
> >> tried FLR first, only falling back to the other methods as "emulation",
> >> I could certainly agree with the file name chosen.
> > Currently, multiple resets are being invoked (independently) in the context
> > of "xl attach/detach/shutdown/reboot".
> > 
> > - pci_reset_function_locked (invoked by pcistub_put_pci_dev())
> >    This function tries various PCI reset methods including FLR.
> > - pcistub_reset_dev (called by toolsstack based on "do_flr" attribute)
> 
> While related in a certain way, I can't really see how this addresses
> the comment.
> 
> Jan
> 
> 

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