[RFC] Remove AGP support from Radeon/Nouveau/TTM

[Christian König]

Am 11.05.20 um 21:55 schrieb John Paul Adrian Glaubitz:
> Hi Christian!
>
>> Well let's face it AGP is a total headache to maintain and dead for at least 10+ years.
>>
>> We have a lot of x86 specific stuff in the architecture independent graphics memory management
>> to get the caching right, abusing the DMA API on multiple occasions, need to distinct between
>> AGP and driver specific page tables etc etc...
> AGP isn't exclusively used on x86 but there are also a lot of PowerPC desktop machines (Apple
> PowerMac, Pegasos etc) that employ AGP graphics.

I unfortunately only have an x86 Mac to test this on, but as far as I 
know the Radeon AGP support for PowerPC is disabled for years already 
because it didn't worked reliable.

>> So the idea here is to just go ahead and remove the support from Radeon and Nouveau and
>> then drop the necessary code from TTM.
>> For Radeon this means that we just switch over to the driver specific page tables and
>> everything should more or less continue to work.
>>
>> For Nouveau I'm not 100% sure, but from the code it of hand looks like we can do it similar to Radeon.
>>
>> Please comment what you think about this.
> I would be against such a move as AGP graphics is still used by people running the powerpc
> and ppc64 Debian ports on their vintage hardware [1].

Please note that at least the Mac I was able to test with Radeon 
hardware just continuous to work. But it is certainly possible that some 
pre r3xx generation hardware will break with this.

We just stop using this bogus idea of trying to use uncached system 
memory as "extension" of the on board video memory and instead switch to 
the reliable device internal GART.

Maybe we should just deprecate the configuration option first?

> I have also CC'ed the debian-powerpc mailing list so that other users can voice their
> opinion.

Thanks for that.

Regards,
Christian.

>
> Thanks,
> Adrian
>
>> [1] https://cdimage.debian.org/cdimage/ports/2020-04-19/