linux-kernel - Re: RFC: vfio-pci API for PCI bus/slot (hot) resets

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Message-ID: <CAErSpo42yK=K55J30V3xd_Ki6KEUOU6q7sUpNrAYe517=CdiDA@mail.gmail.com>
Date:	Fri, 2 Aug 2013 16:49:27 -0600
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:	Alex Williamson <alex.williamson@...hat.com>,
	kvm <kvm@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Alexey Kardashevskiy <aik@...abs.ru>,
	Gavin Shan <shangw@...ux.vnet.ibm.com>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>
Subject: Re: RFC: vfio-pci API for PCI bus/slot (hot) resets

[+cc linux-pci]

On Fri, Aug 2, 2013 at 3:28 PM, Benjamin Herrenschmidt
<benh@...nel.crashing.org> wrote:

> Right. Another use case is, I know of devices that need a fundamental
> reset (PERST) after applying a FW update.

This is a tangent from the real discussion here, but the question of
resetting a device after a firmware update concerns me.  Many if not
all of our current reset interfaces save & restore the architected
parts of config space around the reset.  But a reset after a firmware
update may change things like the number and type of BARs or even the
functionality of the device, so I don't think the restore is safe in
general.

I doubt this is a big problem in general, but I have found reports of
people having to do a system reset or reboot after updating, e.g.,
FPGA images.  I suppose at least some of these could be worked around
with the right hotplug incantations.

http://forums.xilinx.com/t5/PCI-Express/PC-is-hung-if-run-the-second-program-FPGA-by-JTAG/td-p/20871
http://www.alteraforum.com/forum/archive/index.php/t-28477.html
http://www.alteraforum.com/forum/showthread.php?t=35091
https://github.com/NetFPGA/NetFPGA-public/wiki/Restore-PCIE-Configuration
http://lkml.indiana.edu/hypermail/linux/kernel/1104.3/02544.html
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