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Date:   Wed, 8 Nov 2017 19:38:08 +0200
From:   Pasi =?iso-8859-1?Q?K=E4rkk=E4inen?= <pasik@iki.fi>
To:     Govinda Tatti <govinda.tatti@oracle.com>
Cc:     Jan Beulich <JBeulich@suse.com>,
        Konrad Wilk <konrad.wilk@oracle.com>,
        Juergen Gross <jgross@suse.com>,
        xen-devel@lists.xenproject.org,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        linux-kernel@vger.kernel.org
Subject: Re: [Xen-devel] [PATCH] Xen/pciback: Implement PCI slot or bus reset
 with 'do_flr' SysFS attribute
Message-ID: <20171108173808.GH20756@reaktio.net>
References: <20171106174842.20276-1-Govinda.Tatti@Oracle.COM>
 <5A01D3F3020000780018CE86@prv-mh.provo.novell.com>
 <8940b38d-715c-9fcb-cc74-46574d416703@oracle.com>
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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@Oracle.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@lists.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?

If the PCI device in question has native flr capability, then native flr is used, right ? 
I guess I should read the full patch.. 

-- Pasi


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