Re: [Qemu-devel] [PATCH RFC] docs: add PCIe devices placement guidelines

[Marcel Apfelbaum]

On 09/07/2016 10:53 AM, Laszlo Ersek wrote:
> On 09/06/16 13:35, Gerd Hoffmann wrote:
> >   Hi,

[...]

> > Side note: the linux kernel allocates io space nevertheless, so
> > checking /proc/ioports after boot doesn't tell you what the firmware
> > did.
>
> Yeah, we've got to convince Linux to stop doing that. Earlier Alex
> mentioned the "hpiosize" and "hpmemsize" PCI subsystem options for the
> kernel:
>
>           hpiosize=nn[KMG]        The fixed amount of bus space which is
>                           reserved for hotplug bridge's IO window.
>                           Default size is 256 bytes.
>           hpmemsize=nn[KMG]       The fixed amount of bus space which is
>                           reserved for hotplug bridge's memory window.
>                           Default size is 2 megabytes.
>
> This document (once complete) would be the basis for tweaking that stuff
> in the kernel too. Primarily, "hpiosize" should default to zero, because
> its current nonzero default (which gets rounded up to 4KB somewhere) is
> what exhausts the IO space, if we have more than a handful of PCI
> Express downstream / root ports.
>
> Maybe we can add a PCI quirk for this to the kernel, for QEMU's PCI
> Express ports (all of them -- root, upstream, downstream).

Yes, once we will have our "own" controllers and not Intel emulations as today.

Thanks,
Marcel

> Thanks
> Laszlo