linux-kernel - Re: [PATCH 4/4] PCI/sysfs: Allow userspace to query and set device reset mechanism

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Message-ID: <20210315153341.miip637z35mwv7fv@archlinux>
Date:   Mon, 15 Mar 2021 21:03:41 +0530
From:   Amey Narkhede <ameynarkhede03@...il.com>
To:     Leon Romanovsky <leon@...nel.org>
Cc:     alex.williamson@...hat.com, linux-pci@...r.kernel.org,
        bhelgaas@...gle.com, raphael.norwitz@...anix.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/4] PCI/sysfs: Allow userspace to query and set device
 reset mechanism

On 21/03/15 05:07PM, Leon Romanovsky wrote:
> On Mon, Mar 15, 2021 at 08:34:09AM -0600, Alex Williamson wrote:
> > On Mon, 15 Mar 2021 14:52:26 +0100
> > Pali Rohár <pali@...nel.org> wrote:
> >
> > > On Monday 15 March 2021 19:13:23 Amey Narkhede wrote:
> > > > slot reset (pci_dev_reset_slot_function) and secondary bus
> > > > reset(pci_parent_bus_reset) which I think are hot reset and
> > > > warm reset respectively.
> > >
> > > No. PCI secondary bus reset = PCIe Hot Reset. Slot reset is just another
> > > type of reset, which is currently implemented only for PCIe hot plug
> > > bridges and for PowerPC PowerNV platform and it just call PCI secondary
> > > bus reset with some other hook. PCIe Warm Reset does not have API in
> > > kernel and therefore drivers do not export this type of reset via any
> > > kernel function (yet).
> >
> > Warm reset is beyond the scope of this series, but could be implemented
> > in a compatible way to fit within the pci_reset_fn_methods[] array
> > defined here.  Note that with this series the resets available through
> > pci_reset_function() and the per device reset attribute is sysfs remain
> > exactly the same as they are currently.  The bus and slot reset
> > methods used here are limited to devices where only a single function is
> > affected by the reset, therefore it is not like the patch you proposed
> > which performed a reset irrespective of the downstream devices.  This
> > series only enables selection of the existing methods.  Thanks,
>
> Alex,
>
> I asked the patch author here [1], but didn't get any response, maybe
> you can answer me. What is the use case scenario for this functionality?
>
> Thanks
>
> [1] https://lore.kernel.org/lkml/YE389lAqjJSeTolM@unreal
>
Sorry for not responding immediately. There were some buggy wifi cards
which needed FLR explicitly not sure if that behavior is fixed in
drivers. Also there is use a case at Nutanix but the engineer who
is involved is on PTO that is why I did not respond immediately as
I don't know the details yet.

Thanks,
Amey