[coreboot] Native init for AMD cards

[David Hubbard]

On Mon, May 27, 2013 at 11:46 PM, ron minnich <rminnich at gmail.com> wrote:
>
> On Mon, May 27, 2013 at 9:45 PM, David Hubbard
> <david.c.hubbard+coreboot at gmail.com> wrote:
>
> > 1. How hard would it be to import the kernel code into coreboot
directly?
> >
>
> don't. You should do a lot of extraction using coccinelle. And even
> then, there's lots of work to do. I hope to start commits next week
> and hopefully this will provide some ideas.

Ok I'll not pull the entire radeon driver. :)


> > 3. It feels wrong to add so much code to coreboot.
>
> So, don't add it. The i915 support is slowly boiling down to a few
> hundred lines and that should be your goal.

This sounds right. The i915 support is boiled down to just lighting up the
connected displays and setting up a linear framebuffer?

There is a balance, since the radeon driver does not come with extensive,
complete documentation like i915. A successful project will most likely
need to rely on the open source radeon driver upstream for the time being.


> Also, the kernel uses
> generic code to switch to device specific functions. That makes sense
> for a kernel, because it boots on many chipsets and many vga devices.
> It makes no sense for firmware, because we have so much we already
> know -- what chipset, what vga, etc.. Remove generic code and create
> device specific functions with a reasonable API.

Unless a larger team is available, it seems wiser to limit the complexity
of the problem by applying the linux radeon driver. I mean, keep it as
intact as possible and remove the unneeded code. That should even be
compatible with the i915 API, namely modesetting and linear framebuffer for
grub2.


Here's a way to slice the code:

Some low-level parts are nicely self-contained and can be incorporated
without much work: atombios and CRTC for example.

Coccinelle can be used to remove the unneeded code from the asic-specific
files.

The primary init function can be rewritten as a boiled-down set of calls to
the pieces provided by coccinelle.


The big caveat --

We may not know ahead of time what type of GPU it is. It is possible for
.config to select a GPU, but it seems smarter for .config to enable radeon
support -- which supports all radeon GPUs.

If the user switches their GPU (or APU) later, imho coreboot should still
boot. This is in line with what existing BIOSes do.


> > Is a modular approach better? A payload to modeset or some sort of
driver
> > model would be nice.
>
> No, what's best is a simple set of functions with a simple API. See
> superio for example. Or give it 2 more weeks and see what is coming
> :-)

Yes, stripping radeon down makes sense.

What's coming in 2 weeks? What commits are you working on for next week?




On Tue, May 28, 2013 at 10:24 AM, Rudolf Marek <r.marek at assembler.cz> wrote:
> Alex told me:
>
> The AsicInit table just performs low level setup on the asic, it doesn't
mess with the displays at all.  The radeon vbios has real mode x86 code
that gets executed at post or via vbe calls to read in the information in
the atombios tables, figure out the display topology and detect and light
up whatever displays are attached.  You would need to implement that
functionality in your vbios replacement.  If you want a bios console,
you'll have to use the open source radeon driver as a guide to how to write
a vbios replacement that enumerates and lights up the displays.
>
> END

The open source radeon driver is a good place to start.


>
> Also it turned out that the bytecode is there for the OEM so the changed
topology does not need the new VBIOS assembly but just the AtomBIOS
bytecode.
> Which is quite bad, because the VBIOS  is depending on how it is routed
and may only work with similar boards even when chipset is same. We would
have to find out a way how to include the AtomBIOS in some form in the
coreboot or re-write it somehow, because the bytecode is not even
"property" of AMD but OEM and radeon driver needs that to be present in a
rom. Maybe it would be possible to write some commmon init and handle just
small changes in the bytecode.
>
> For now, I would say kind of "reply" init might work, it depends if your
goals are similar like we have with intel, so just graphic framebuffer for
grub2 or something like I had in my mind.

Yes, I think just a framebuffer for grub2 is more than enough to take on
right now.


Regards,
David
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