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

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Message-ID: <20171129180529.GQ20756@reaktio.net>
Date:   Wed, 29 Nov 2017 20:05:29 +0200
From:   Pasi Kärkkäinen <pasik@....fi>
To:     Govinda Tatti <govinda.tatti@...cle.com>
Cc:     Jan Beulich <JBeulich@...e.com>,
        Konrad Wilk <konrad.wilk@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        xen-devel@...ts.xenproject.org,
        Boris Ostrovsky <boris.ostrovsky@...cle.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 11:25:09AM -0600, Govinda Tatti wrote:
> 
> >>>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.
>
> pcistub_reset_dev() just tries slot or bus reset but not FLR since it is
> being
> checked and executed by pci_reset_function_locked() if supported. May be we
> can
> add FLR reset code to pcistub_reset_dev() and try FLR first before fall-back
> to
> slot/bus reset.
>

Hmm.. is the suitable reset method something that can be figured out automatically?

I mean if FLR is tried first, but it isn't supported by the device, is it OK to go ahead and do a slot/bus reset automatically?
What if there are other devices in the same bus, wouldn't automatic bus reset be a bad thing? 

Or should the reset-method be configured by the user for the VM / PCI device ? 

Just thinking out loud here..


> Cheers
> GOVINDA
> 


Thanks,

-- Pasi