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

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Date:   Mon, 15 Mar 2021 17:07:14 +0200
From:   Leon Romanovsky <leon@...nel.org>
To:     Alex Williamson <alex.williamson@...hat.com>
Cc:     Pali Rohár <pali@...nel.org>,
        Amey Narkhede <ameynarkhede03@...il.com>, bhelgaas@...gle.com,
        raphael.norwitz@...anix.com, linux-kernel@...r.kernel.org,
        linux-pci@...r.kernel.org
Subject: Re: [PATCH 4/4] PCI/sysfs: Allow userspace to query and set device
 reset mechanism

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

>
> Alex
>