Re: [Qemu-devel] Question about qemu firmware configuration (fw_cfg) device

[Gleb Natapov]

On Sun, Jul 18, 2010 at 07:26:57PM +0200, Alexander Graf wrote:
> 
> On 17.07.2010, at 11:53, Richard W.M. Jones wrote:
> 
> > On Sat, Jul 17, 2010 at 10:50:59AM +0100, Richard W.M. Jones wrote:
> >> I understand from the git logs that fw_cfg was added because the old
> >> way was to load kernel & initrd into RAM directly, but this didn't
> >> work because SeaBIOS would clear the RAM, clobbering kernel & initrd.
> >> Could we change to loading these directly into RAM, and instead
> >> provide some indication to SeaBIOS so it doesn't clobber the RAM?  I'm
> >> quite prepared to do the work, just wondering if there's something
> >> else I'm not getting about this.
> > 
> > Or thinking around the subject:
> > 
> > Change fw_cfg so that you send a command + a physical address, and
> > fw_cfg memcpy's the kernel / initrd / etc to that physical address.
> > Then linuxboot.bin doesn't have to do the manual copying.
> > 
> > Or just change linuxboot.bin so it does 32 bit inl instructions, which
> > might at least be a bit faster ...
> 
> I don't see why it would be slow. ins should be emulated using coalesced 
> mmio, no?
> 
Coalesced mmio is for mmio, not pio. But we do try to optimize pio
string instructions otherwise loading of 100M would take hours.

--
                        Gleb.