[SeaBIOS] [PATCHv6 00/16] boot order specification

Kevin O'Connor kevin at koconnor.net
Tue Nov 30 02:55:09 CET 2010

On Mon, Nov 29, 2010 at 11:50:45AM +0100, Gerd Hoffmann wrote:
> >>If scsi card has optionrom with only one bcv then Seabios can determine
> >>its boot order from device path, so why not provide user with this
> >>option today?
> >It's unclear to me how SeaBIOS is supposed to do that.
> Try to keep track of which bcv/bev belongs to which pci device?  It
> should surely work for devices supported by seabios natively.

No issues for any device with native support.  I'm okay with the
proposed syntax.

> SeaBIOS should also know which device's rom registered which entry.

It doesn't today, but that shouldn't be an issue to add.

> It might become tricky though in case there are multiple identical
> devices are present, say two e1000 cards, where the first rom could
> register entries for both cards ...

Right - here's where things get complicated.

> >Maybe we can compromise here - if the user selects booting from a
> >device, and qemu sees there is a rom for that device, then qemu can
> >specify two boot options:
> >
> >/pci at i0cf8/ethernet at 4/ethernet-phy at 0
> >/pci at i0cf8/rom at 4
> >
> >SeaBIOS will ignore the first entry, and act on the second entry.
> SeaBIOS should be able to operate just fine with the first entry.
> "ethernet at 4" means "the nic at bus address 4".  As this is a PCI bus
> "4" is the pci address.  So SeaBIOS would just look what entries it
> has for "00:04.0", run the rom, and ignore the "/ethernet-phy at 0"
> part as it can't handle it.

Right - I'm not happy about trying to parse out openbios device
descriptors though.  The natural flow (as I see it) is for seabios to
find all the boot methods in the system and then see which ones have
been requested to be prioritized.  Trying to do fuzzy matching of
found device to requested device just seems like an unnecessary pain

>When booting via rom it can either just pick
> the first entry unconditionally (probably good enougth in 99% of the
> cases) or do some guesswork based on the order the entries are
> registered.

I guess that's the crux of the matter - I'd rather not do guessing in
the firmware.  The emulator is in a much better position to do
heuristics and guessing - if nothing else, the emulator can allow the
user to pass it in on the command-line.

> >BTW, how are PCI locations specified in these paths?  They should have
> >a (bus, dev, fn) - your examples only seem to show dev.  How are the
> >other parts specified?
> fn is optional for fn=0, IIRC the syntax is "$class@$dev,$fn".
> Bus is specified via location in the tree, i.e. you'll see the
> bridge for the secondary pci bus in the path, like this:
> /pci at i0cf8/bridge at 7/ethernet at 3/...
> (not sure it is actually named 'bridge' in the openfirmware specs though).



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