Re: [coreboot] How does SeaBIOS transition to Linux?

[Peter Stuge]

Zoran Stojsavljevic wrote:
> crucial question from me: how Coreboot will work if instead SeaBIOS
> GRUB2 is the payload chosen

Instead of SeaBIOS reading MBR, GRUB2 will read its configuration
file and operate accordingly.

//Peter

How does SeaBIOS transition to Linux?

[Zoran Stojsavljevic]

Hello Peter,

Did not understand... I must admit! As of my best interpretation SeaBIOS
has 5 functions which makes BIOS legacy:

get and set variables, get and set real time clock, reset.

Or maybe, something changed.

I went back, to inspect CSM code in SeaBIOS, and found the following:

#

# General Features

#

# CONFIG_COREBOOT is not set

# CONFIG_QEMU is not set

*CONFIG_CSM=y <<==================== set CSM ON*

# CONFIG_QEMU_HARDWARE is not set

CONFIG_THREADS=y

CONFIG_RELOCATE_INIT=y

CONFIG_BOOTMENU=y

CONFIG_BOOTSPLASH=y

CONFIG_BOOTORDER=y

CONFIG_ENTRY_EXTRASTACK=y

CONFIG_MALLOC_UPPERMEMORY=y

CONFIG_ROM_SIZE=0

Then make:

Compile checking out/src/hw/pcidevice.o
  Compile checking out/src/hw/ahci.o
  Compile checking out/src/hw/pvscsi.o
  Compile checking out/src/hw/usb-xhci.o
  Compile checking out/src/hw/usb-hub.o
  Compile checking out/src/hw/sdcard.o
  Compile checking out/src/fw/coreboot.o
  Compile checking out/src/fw/lzmadecode.o
  Compile checking out/src/fw/multiboot.o
  *Compile checking out/src/fw/csm.o*
  Compile checking out/src/fw/biostables.o
  Compile checking out/src/fw/paravirt.o
  Compile checking out/src/fw/shadow.o
  Compile checking out/src/fw/pciinit.o
  Compile checking out/src/fw/smm.o
  Compile checking out/src/fw/smp.o
  Compile checking out/src/fw/mtrr.o
  Compile checking out/src/fw/xen.o
  Compile checking out/src/fw/acpi.o
  Compile checking out/src/fw/mptable.o
  Compile checking out/src/fw/pirtable.o
  Compile checking out/src/fw/smbios.o

Where I see e820 table which is to be passed to OS, in order OS to
understand what memory it can use. But I did not find explicitly these 5
functions. So I need a little help here. Where are these functions?

Now... How GRUB2 replaces all of these functionalities? I see what you said
here (that GRUB2 is directly implemented into FW, thus skipping MBR), but
who/what entity is replacing missing SeaBIOS functionalities?

Thank you,
Zoran

On Sat, Feb 11, 2017 at 2:18 PM, Peter Stuge  wrote:
> Zoran Stojsavljevic wrote:
> > crucial question from me: how Coreboot will work if instead SeaBIOS
> > GRUB2 is the payload chosen
>
> Instead of SeaBIOS reading MBR, GRUB2 will read its configuration
> file and operate accordingly.
>
> //Peter