Re: X server support?

[Michael Lorenz <macallan%netbsd.org@localhost>]

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Hello,

On Sep 10, 2008, at 1:22 PM, Tim Rightnour wrote:

> On 10-Sep-2008 Michael Lorenz wrote:
> > Basically - look at genfb_pci.c, grep it for PCI_MAGIC_IO_RANGE, pick
> > an offset that's safe on your hardware ( it may or may not correspond
> > to the real bus address of the PCI IO space but X and genfb need to
> > agree about it and no PCI BARs should EVER be mapped there ). Put
> > #define PCI_MAGIC_IO_RANGE 0xwhatever
> > into param.h and rebuild both X and the kernel.
> > If 0xf2000000 is safe just use it and you can use macppc's binaries.
>
> Will this trick only work with genfb, or is it a general support  
> mechanisim?
>
> Either way, I believe 0xf2000000 will work.

All 'my' framebuffer drivers support it. That includes machfb,  
voodoofb, chipsfb, r128fb, shark's console code, radeonfb and genfb  
at pci.
X expects to mmap 64kB IO space at PCI_MAGIC_IO_RANGE - although many  
macs implement considerably more ( 8MB on bandit for instance ) I've  
never seen any (Open)Firmware - apple or not - map any IO BAR above  
0xffff so 64kB should be enough.
What the drivers do is simply this - in their mmap() methods they  
return the physical address that corresponds to the IO tag belonging  
to the PCI bus the graphics chip belongs to. This is necessary since  
many macs have more than one PCI host bridge and each implements its  
own IO space ( same goes for Suns with two Psychos for instance )
That way X can map the right IO space through /dev/ttyE0 without any  
knowledge of the underlying PCI bus, host bridges and so on.
0xf2000000 just happens to be the address where the 1st bandit's IO  
space would be on a 1st generation PCI PowerMac ( the 2nd bandit  
would have its IO space at 0xf4000000, there's address space reserved  
for up to four bandits ), on all newer models this address range is  
either reserved, used for PCI IO space or used for something not PCI  
related so it will never collide with any valid BAR.
Also, this mechanism isn't PCI specific, shark's graphics chip sits  
on a VL bus.

have fun
Michael

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