[SeaBIOS] [PATCH 2/2] accept MADT over fw_cfg

Kevin O'Connor kevin at koconnor.net
Tue Apr 23 02:38:58 CEST 2013

On Mon, Apr 22, 2013 at 10:03:01AM +0300, Michael S. Tsirkin wrote:
> On Sun, Apr 21, 2013 at 08:39:41PM -0400, Kevin O'Connor wrote:
> > On Sun, Apr 21, 2013 at 11:41:48PM +0300, Michael S. Tsirkin wrote:
> > > Okay I'm pretty close to posting some patches
> > > that advance this project further, but wanted to
> > > check something beforehand: there are several tables
> > > that point to other tables (for example: FADT points
> > > to DSDT). What I did is provide a list of fixups
> > > such that bios can patch in pointers without
> > > any need to understand what's what.
> > > Thoughts?
> > 
> > For the RSDP, RSDT, and FADT I think SeaBIOS should just update those
> > tables to set the pointers within them and then recalculate the
> > checksum.  I don't think anything complex is needed - it's easy for
> > SeaBIOS to recognize those special tables and modify them.
> True, that's simple enough.  My worry is we can add more such tables.
> For example, we can decide to switch to XSDT in the future.

I know of the following quirks that would have to be handled:

1 - the RSDP must be in the f-segment (where as all other tables can
go into "high" memory).

2 - the RSDP has a checksum in a different location from the other
tables and (with an XSDT) it can have two checksums.

3 - the RSDP has a pointer to the RSDT (and to the XSDT if present).

4 - the RSDT (and XSDT if present) has pointers to all the other
tables (except RSDP, RSDT, DSDT, and FACS).  The FADT pointer must be
first in the list.

5 - the FADT table has pointers to DSDT and FACS.

6 - the FACS table must be 64 byte aligned.

So, will a generic scheme really be able to handle all of the above
quirks, or will we just be mixing some hardcoded quirks with some
generic quirks?  And, will the code to handle the above quirks in a
generic fashion be of a higher complexity than simply hard-coding it?


More information about the SeaBIOS mailing list