POSTing of video cards (WAS: Solo Xgl..)

[Benjamin Herrenschmidt]

On Mon, 2005-02-21 at 23:42 -0500, Jon Smirl wrote:
> On Tue, 22 Feb 2005 14:12:48 +1100, Benjamin Herrenschmidt
> <benh at kernel.crashing.org> wrote:
> > It's up to each driver to detect wether it's card need to be POSTed or
> > not. Anything else would mean infinite breakage.
> 
> Your approach is that it is a per driver problem. I was taking a
> different tack and looking at it as a BIOS deficiency that should be
> compensated for. There is already code in the kernel for identifying
> the boot video device.

Your assumption is rather specific to a given platform... what if you
have a card with no ROM (embedded system) but your kernel has a copy of
what should be the ROM at hand ? (flash is expensive, heh :)

> I was working on the assumption that all PCI based, VGA class hardware
> that is not the boot device needs to be posted.

That isn't the case on all platforms. Also, I like the flexibility of
having a userland helper since that doesn't "tie" us to the semantics of
an x86 platform & BIOS (we could have an OF emulator too, or whatever
binary program provided by the vendor in userspace to reinit the card
without having to link that with the kernel).

I think my approach is the most flexible in the long run.

> And that the posting should occur before the drivers are
> loaded. In order words the BIOS should have provided initialized
> hardware but since it didn't we can apply a fixup in the PCI driver. I
> also suspect there may be SCSI disk controller cards that need the
> same procedure.

I don't think we have to do these assumptions. It should really be under
driver control.

> I have no strong opinions on how to fix the post problem, I just want
> to make sure the problem is fully discussed by the relevant people and
> a consensus solution is achieved. I'm not sure that all of the core
> kernel developers that might be impacted by this have considered all
> of the options. I would like to try and get a consensus design and
> avoid reimplementing everything ten times.

Agreed.

Ben.