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

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Message-ID: <20210315083409.08b1359b@x1.home.shazbot.org>
Date:   Mon, 15 Mar 2021 08:34:09 -0600
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Pali Rohár <pali@...nel.org>
Cc:     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, 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