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Re: [Qemu-devel] [PATCH] hw/pci: do not update the PCI mappings while De


From: Marcel Apfelbaum
Subject: Re: [Qemu-devel] [PATCH] hw/pci: do not update the PCI mappings while Decode (I/O or memory) bit is not set in the Command register
Date: Thu, 14 Jan 2016 19:20:32 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0

On 01/14/2016 05:37 PM, Michael S. Tsirkin wrote:
On Thu, Jan 14, 2016 at 05:23:27PM +0200, Marcel Apfelbaum wrote:
On 01/14/2016 04:49 PM, Michael S. Tsirkin wrote:
On Thu, Jan 14, 2016 at 03:30:41PM +0100, Laszlo Ersek wrote:
2. The same as with pxb, disable Integrated End points for pxb-pcie.

My vote, without a doubt.

Yea, me too.


On a related note: I wonder whether enough resources will be allocated
to the bridge to actually make it possible to add devices by hotplug
later.


It works the same as with PXB, but now instead of having one internal 
PCI-bridge,
we will have several switches/root ports. Each of them will get the minimum MEM 
required by
PCI bridges,

what does this mean? What if you add a bunch of devices
with large memory BARs? They won't fit will they?


Indeed, devices with over 1 MB (I think) BARs can't be hot-plugged.
This is a known design limitation. We can think of a way to handle this,
but the real reason we have multiple root bridges is to be able to
correlate an assigned device with a NUMA node. In this case the device
will be added more likely at boot time.


I think the first step is to have *some* hot-plug support for pxb/pxb-pcie
with the current constraints, once it works we can think
of a way to make it work for devices with large BARs.

Thanks,
Marcel

however the IO will be allocated only if at least one legacy device
will be present at boot time. (this is at least what SeaBIOS does, I am going 
to check OVMF actions)

Also related, checking that PCIe native hotplug works for devices behind
pxb-pcie bridges is my next step after I fix the current issue.

Thanks,
Marcel



I am going to look at 1., maybe I is doable in a clean way.

My vote: don't. :)

Thanks
Laszlo

Thanks,
Marcel


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