Re: [Qemu-devel] PCI(e): Documentation "io-reserve" and related properties?

[Marcel Apfelbaum <marcel.apfelbaum@gmail.com>]

On 6/11/19 10:21 AM, Kashyap Chamarthy wrote:
> On Thu, Jun 06, 2019 at 02:20:18PM -0400, Michael S. Tsirkin wrote:
>> On Thu, Jun 06, 2019 at 06:19:43PM +0200, Kashyap Chamarthy wrote:
>>> Hi folks,
>>>
>>> Today I learnt about some obscure PCIe-related properties, in context of
>>> the adding PCIe root ports to a guest, namely:
>>>
>>>      io-reserve
>>>      mem-reserve
>>>      bus-reserve
>>>      pref32-reserve
>>>      pref64-reserve
>>>
>>> Unfortunately, the commit[*] that added them provided no documentation
>>> whatsover.
>>>
>>> In my scenario, I was specifically wondering about what does
>>> "io-reserve" mean, in what context to use it, etc.  (But documentation
>>> about other properties is also welcome.)
>>>
>>> Anyone more well-versed in this area care to shed some light?
>>>
>>>
>>> [*] 6755e618d0 (hw/pci: add PCI resource reserve capability to legacy
>>>      PCI bridge, 2018-08-21)
>> So normally bios would reserve just enough io space to satisfy all
>> devices behind a bridge. What if you intend to hotplug more devices?
>> These properties allow you to ask bios to reserve extra space.
> Thanks.  Would be useful to have them documented in the official QEMU
> command-line documentation.  Otherwise, they will remain as arcane
> properties that barely anyone knows about.
>

There is some documentation under qemu/docs/pcie_pci_bridge.txt.
I agree there is always room for QEMU cmd-line improvement.

Thanks,
Marcel