Re: [SeaBIOS] [RFC PATCH v2 4/4] pci: enable RedHat PCI bridges to reserve additional buses on PCI init

[Gerd Hoffmann]

On Sun, 2017-07-23 at 22:44 +0300, Alexander Bezzubikov wrote:
> By the way, any ideas on how to avoid 'bus overstealing' would 
> be greatly appreciated.
> Static BIOS variable isn't applicable since its value isn't saved
> across reboots.

I think the reservation hints should be a absolute number, not a
increment.  i.e. if qemu suggests to reserve three extra bus numbers
seabios should reserve three, no matter whenever there are zero, one,
two or three child busses present.  And I guess seabios should
interpret that as minimum, so in case it finds five child busses it
will allocate five bus numbers of course ...

Same with the other limit hints.  If the hint says to allocate 16M, and
existing device bars sum up to 4M, allocate 16M (and therefore leave
12M address space for hotplug).  If the device bars sum up to 32M,
allocate that.

While being at it:  I have my doubts the capability struct layout
(which mimics register layout) buys us that much, seabios wouldn't
blindly copy over the values anyway.  Having regular u32 fields looks
more useful to me.

cheers,
  Gerd

[RFC PATCH v2 4/4] pci: enable RedHat PCI bridges to reserve additional buses on PCI init

[Alexander Bezzubikov]

2017-07-24 12:42 GMT+03:00 Gerd Hoffmann :
> On Sun, 2017-07-23 at 22:44 +0300, Alexander Bezzubikov wrote:
> > By the way, any ideas on how to avoid 'bus overstealing' would
> > be greatly appreciated.
> > Static BIOS variable isn't applicable since its value isn't saved
> > across reboots.
>
> I think the reservation hints should be a absolute number, not a
> increment.  i.e. if qemu suggests to reserve three extra bus numbers
> seabios should reserve three, no matter whenever there are zero, one,
> two or three child busses present.  And I guess seabios should
> interpret that as minimum, so in case it finds five child busses it
> will allocate five bus numbers of course ...

Personally I have nothing against it. Marcel, Michael, what do you think?
> Same with the other limit hints.  If the hint says to allocate 16M, and
> existing device bars sum up to 4M, allocate 16M (and therefore leave
> 12M address space for hotplug).  If the device bars sum up to 32M,
> allocate that.
>
> While being at it:  I have my doubts the capability struct layout
> (which mimics register layout) buys us that much, seabios wouldn't
> blindly copy over the values anyway.  Having regular u32 fields looks
> more useful to me.

Again, if nobody has any objections, I can change it in v3.
> cheers,
>   Gerd