[Qemu-devel] Re: [PATCH] [Seabios] Over 4GB address ranges for 64bit PCI BARs

[Isaku Yamahata <yamahata@valinux.co.jp>]

On Mon, Nov 08, 2010 at 04:35:38PM +1300, Alexey Korolev wrote:
> > - >4GB 64bit bar allocation
> >   Your patche tries to address this issue. But it breaks PCI-to-PCI
> >   bridge filtering support.
> Hmm, it is quite possible, as we don't know a lot about seabios PCI-to-PCI bridge filtering support.
> Just out of curiosity: what is the issue?

It's pci_bios_init_device_bridge() in pciinit.c.
The function touches pci_bios_io_addr, pci_bios_mem_addr, and
pci_bios_prefmem_addr.
So we need to modify, not only pci_bios_allocate_region(),
but also pci_bios_init_device_bridge().

The function programs the P2P bridge to forward IO/memory access
on primary pci bus to secondary pci bus.
It needs to be aware of 64bit BAR allocation.


> >   If the BAR size is huge (or there are too many BARs), the bar can't
> >   be allocated under 4G. So several persons want seabios to allocate
> >   such BARs at >4GB area complaining that OS can't use BARs that seabios
> >   didn't assigned.
> > 
> >   Others think such BAR can be left unallocated.
> >   Seabios role is to setup minimal basic environment for bootloader
> >   to boot OS, 64bit bar allocation is beyond it's role.
> >   bootloader/rombios usually doesn't handle BARs that is allocated
> >   beyond 4GB, and Modern OSes can re-arrange PCI bar allocation itself.
> >   So 64bit bar allocation support wouldn't be needed.
> > 
> >   I'm not sure if there is enough demand to support 64bit BAR allocation
> >   and if Kevin will accept it or not. Consensus is needed.
> >   What OS are you using?
> > 
> For us >4GB allocation is welcome but not critical, because we mainly
> use Linux versions 2.6.18 and newer. We've tested the seabios without
> assignment of the regions which do not fit in first 32bit and it appears
> to work fine. So for us 64bit bar allocation support wouldn't be needed.
> 
> It is possible that people will use an ancient version of Linux, but the
> probability of this event is very low.

My position is same to yours. Welcome, but not critical.
So the issue is, who will finish it.
-- 
yamahata