Does SeaBIOS uses the BIOS interfaces itself?

[Paul Menzel]

Dear SeaBIOS folks,

looking at

$ more src/Kconfig
[…]
    config AHCI
        depends on DRIVES
        bool "AHCI controllers"
        default y
        help
            Support for AHCI disk code.
[…]

disabling the »Drive interface« (which sets(?) `DRIVES`) in the menu
BIOS interfaces, support for booting from an AHCI device is disabled
too.

So for my understanding, in the current implementation SeaBIOS uses its
own BIOS interfaces although strictly it would not be necessary. Is that
correct?

Thanks,

Paul

[Kevin O'Connor]

On Mon, Mar 18, 2013 at 11:57:31AM +0100, Paul Menzel wrote:
> Dear SeaBIOS folks,
>
> looking at
>
> $ more src/Kconfig
> […]
>     config AHCI
>         depends on DRIVES
>         bool "AHCI controllers"
>         default y
>         help
>             Support for AHCI disk code.
> […]
>
> disabling the »Drive interface« (which sets(?) `DRIVES`) in the menu
> BIOS interfaces, support for booting from an AHCI device is disabled
> too.

The dependency is there because there is no use in compiling in a disk
device driver if there is no external interface to access disks.
(What value would there be in having an AHCI driver if the BIOS
doesn't support reading from disks?)
> So for my understanding, in the current implementation SeaBIOS uses its
> own BIOS interfaces although strictly it would not be necessary. Is that
> correct?

I don't understand your question.  Sometimes SeaBIOS calls external
16bit disk interfaces when it wishes to read from a drive - but it
does this only for compatibility (to handle the cases where an option
ROM could have hooked the 16bit disk interrupt and substituted its own
code in place of the SeaBIOS code).  This is not related to the
Kconfig dependency however (see above).

-Kevin

[Paul Menzel]

Am Dienstag, den 19.03.2013, 19:17 -0400 schrieb Kevin O'Connor:
> On Mon, Mar 18, 2013 at 11:57:31AM +0100, Paul Menzel wrote:
> > Dear SeaBIOS folks,
> >
> > looking at
> >
> > $ more src/Kconfig
> > […]
> >     config AHCI
> >         depends on DRIVES
> >         bool "AHCI controllers"
> >         default y
> >         help
> >             Support for AHCI disk code.
> > […]
> >
> > disabling the »Drive interface« (which sets(?) `DRIVES`) in the menu
> > BIOS interfaces, support for booting from an AHCI device is disabled
> > too.
>
> The dependency is there because there is no use in compiling in a disk
> device driver if there is no external interface to access disks.
> (What value would there be in having an AHCI driver if the BIOS
> doesn't support reading from disks?)

Hearing of filo or GRUB 2 as payload, I thought these interfaces are not
needed for actual booting. But assuming is not good as Peter pointed
out.
> > So for my understanding, in the current implementation SeaBIOS uses its
> > own BIOS interfaces although strictly it would not be necessary. Is that
> > correct?
>
> I don't understand your question.  Sometimes SeaBIOS calls external
> 16bit disk interfaces when it wishes to read from a drive - but it
> does this only for compatibility (to handle the cases where an option
> ROM could have hooked the 16bit disk interrupt and substituted its own
> code in place of the SeaBIOS code).  This is not related to the
> Kconfig dependency however (see above).

I did not think of the option ROM. Thanks for mentioning it.

Thanks,

Paul