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Re: [Qemu-devel] [PATCH] hw/pci: disable pci-bridge's shpc by default


From: Marcel Apfelbaum
Subject: Re: [Qemu-devel] [PATCH] hw/pci: disable pci-bridge's shpc by default
Date: Thu, 24 Nov 2016 11:39:25 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.1.1

On 11/24/2016 06:06 AM, David Gibson wrote:
On Wed, Nov 23, 2016 at 01:08:46PM +0200, Marcel Apfelbaum wrote:
On 11/22/2016 10:25 PM, Laurent Vivier wrote:


On 22/11/2016 18:26, Marcel Apfelbaum wrote:
On 11/18/2016 05:52 PM, Andrew Jones wrote:
On Wed, Nov 16, 2016 at 07:05:25PM +0200, Marcel Apfelbaum wrote:
On 11/16/2016 06:44 PM, Andrew Jones wrote:
On Sat, Nov 05, 2016 at 06:46:34PM +0200, Marcel Apfelbaum wrote:
On 11/03/2016 09:40 PM, Michael S. Tsirkin wrote:
On Thu, Nov 03, 2016 at 01:05:44PM +0200, Marcel Apfelbaum wrote:
On 11/03/2016 06:18 AM, Michael S. Tsirkin wrote:
On Wed, Nov 02, 2016 at 05:16:42PM +0200, Marcel Apfelbaum wrote:
The shpc component is optional while  ACPI hotplug is used
for hot-plugging PCI devices into a PCI-PCI bridge.
Disabling the shpc by default will make slot 0 usable at boot time

Hi Michael


at the cost of breaking all hotplug for all non-acpi users.


Do we have a non-acpi user that is able to use the shpc component
as-is today?

power and some arm systems I guess?


Adding Andrew , maybe he can give us an answer.

Not really :-) My lack of PCI knowledge makes that difficult. I'd be
happy
to help with an experiment though. Can you give me command line
arguments,
qmp commands, etc. that I should use to try it out? I imagine I should
just boot an ARM guest using DT (instead of ACPI) and then attempt to
hotplug a PCI device. I'm not sure, however, what, if any, special
configuration I need in order to ensure I'm testing what you're
interested in.


Hi Drew,


Just run QEMU with '-device pci-bridge,chassis_nr=1,id=bridge1
-monitor stdio'
with an ARM guest using DT and wait until the guest finish booting.

Then run at hmp:
device_add virtio-net-pci,bus=bridge1,id=net2

Next run lspci in the guest to see the new device.

Thanks for the instructions Marcel. Here's the results

 $QEMU -machine virt,accel=$ACCEL -cpu $CPU -nographic -m 4096 -smp 8 \
       -bios /usr/share/AAVMF/AAVMF_CODE.fd \
       -device pci-bridge,chassis_nr=1,id=bridge1 \
       -drive file=$FEDORA_IMG,if=none,id=dr0,format=qcow2 \
       -device virtio-blk-pci,bus=bridge1,addr=01,drive=dr0,id=disk0 \
       -netdev user,id=hostnet0 \
       -device virtio-net-pci,bus=bridge1,addr=02,netdev=hostnet0,id=net0

 # lspci
 00:00.0 Host bridge: Red Hat, Inc. Device 0008
 00:01.0 PCI bridge: Red Hat, Inc. QEMU PCI-PCI bridge
 01:01.0 SCSI storage controller: Red Hat, Inc Virtio block device
 01:02.0 Ethernet controller: Red Hat, Inc Virtio network device

 (qemu) device_add virtio-net-pci,bus=bridge1,id=net2
 Unsupported PCI slot 0 for standard hotplug controller. Valid slots are
 between 1 and 31.

(Tried again giving addr=03)

 (qemu) device_add virtio-net-pci,bus=bridge1,id=net2,addr=03

(Seemed to work, but...)

 # lspci
 00:00.0 Host bridge: Red Hat, Inc. Device 0008
 00:01.0 PCI bridge: Red Hat, Inc. QEMU PCI-PCI bridge
 01:01.0 SCSI storage controller: Red Hat, Inc Virtio block device
 01:02.0 Ethernet controller: Red Hat, Inc Virtio network device

(Doesn't show up in lscpi. So I guess it doesn't work)


Hi Drew,
Thanks for confirming that it doesn't work.

Michael asked if we can check the same for powerpc before
disabling the shpc by default.

Adding David, Thomas and Laurrent, maybe they have time
to check it for powerpc.

With this patch:

# lspci
00:00.0 PCI bridge: Red Hat, Inc. QEMU PCI-PCI bridge
00:03.0 Unclassified device [00ff]: Red Hat, Inc Virtio memory balloon
address@hidden ~]# QEMU 2.7.90 monitor - type 'help' for more information
(qemu) device_add virtio-net-pci,bus=bridge1,id=net2
Bus 'bridge1' does not support hotplugging
(qemu) device_add virtio-net-pci,bus=bridge1,id=net2,addr=3
Bus 'bridge1' does not support hotplugging

Without this patch:

# lspci
00:00.0 PCI bridge: Red Hat, Inc. QEMU PCI-PCI bridge
00:03.0 Unclassified device [00ff]: Red Hat, Inc Virtio memory balloon
address@hidden ~]# QEMU 2.7.90 monitor - type 'help' for more information
(qemu) device_add virtio-net-pci,bus=bridge1,id=net2
Unsupported PCI slot 0 for standard hotplug controller. Valid slots are
between 1 and 31.
(qemu) device_add virtio-net-pci,bus=bridge1,id=net2,addr=3
(qemu) [   37.342908] shpchp 0000:00:00.0: Latch close on Slot(3)
[   37.342963] shpchp 0000:00:00.0: Button pressed on Slot(3)
[   37.343003] shpchp 0000:00:00.0: Card present on Slot(3)
[   37.344186] shpchp 0000:00:00.0: PCI slot #3 - powering on due to
button press
[   43.361827] shpchp 0000:00:00.0: No new device found


Hi Laurrent,
Thank you for the fast reply!

What I see from the log is that ppc does use the shpc for hotplug,
but there is some implementation bug preventing it to work.

That doesn't sound right.  ppc, or more correctly the pseries machine
type, has it's own hotplug notification mechanism.  If we're trying to
invoke shpc, I think something is wrong.


Hi David,

As you can see the shpc driver claims the pci-bridge slots and it responds
to the hot-plug events.

Anyway, what is the hotplug mechanism preferred by the pseries machine ?

Side note: what we want to understand is if using pci-bridges's shpc  by default
would help non x86 archs (since QEMU x86 machine uses ACPI based hot-plug).

Thanks,
Marcel

Drew, may I trouble one last time for the dmesg?
I think we would see exactly the same log.


Thanks,
Marcel

[   43.361867] shpchp 0000:00:00.0: Cannot add device at 0000:01:03
[   43.363277] shpchp 0000:00:00.0: Latch open on Slot(3)
[   43.363320] shpchp 0000:00:00.0: Button pressed on Slot(3)
[   43.363360] shpchp 0000:00:00.0: Card not present on Slot(3)
[   43.363506] shpchp 0000:00:00.0: PCI slot #3 - powering on due to
button press
[   48.371835] shpchp 0000:00:00.0: No adapter on slot(3)

Laurent







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