Re: [Qemu-devel] [PATCH RFC 0/3] seabios: move acpi table formatting out of bios

[Kevin O'Connor]

On Tue, May 07, 2013 at 09:00:48PM +0300, Michael S. Tsirkin wrote:
> On Thu, Apr 25, 2013 at 12:02:20PM +0300, Michael S. Tsirkin wrote:
> > Untested yet, but I thought I'd share the
> > BIOS bits so we can agree on direction.
> > 
> > In particular check out ROM sizes:
> > - Before patchset with DSDT enabled
> >     Total size: 127880  Fixed: 59060  Free: 3192 (used 97.6% of 128KiB rom)
> > - Before patchset with DSDT disabled
> >     Total size: 122844  Fixed: 58884  Free: 8228 (used 93.7% of 128KiB rom)
> > - After patchset:
> >     Total size: 128776  Fixed: 59100  Free: 2296 (used 98.2% of 128KiB rom)
> > - Legacy disabled at build time:
> >     Total size: 119836  Fixed: 58996  Free: 11236 (used 91.4% of 128KiB rom)
> > 
> > As can be seen from this, most size savings come
> > from dropping DSDT, but we do save a bit by removing
> > other tables. Of course the real reason to move tables to QEMU
> > is so that ACPI can better match hardware.
> > 
> > This patchset adds an option to move all code for formatting acpi tables
> > out of BIOS. With this, QEMU has full control over the table layout.
> > All tables are loaded from the new "/etc/acpi/" directory.
> > Any entries in this directory cause BIOS to disable
> > ACPI table generation completely.
> > A generic linker script, controlled by QEMU, is
> > loaded from "/etc/linker-script". It is used to
> > patch in table pointers and checksums.
> 
> After some thought, there are two additional
> options worth considering, in that they simplify
> bios code somewhat:
> 
> - bios could get size from qemu, allocate a buffer
>   (e.g. could be one buffer for all tables)
>   and pass the address to qemu.
>   qemu does all the patching
> 
> - further, qemu could do the copy of tables into
>   that address directly

This seems more complex than necessary to me.

The important task is to get the tables generated in QEMU - I'd focus
on getting the tables generated in QEMU (one table per fw_cfg "file").
Once that is done, the SeaBIOS side can be easily implemented, and we
can add any enhancements on top if we feel it is necessary.

-Kevin