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

[Alex Deucher <alexdeucher@gmail.com>]

On Mon, May 11, 2020 at 4:02 PM John Paul Adrian Glaubitz
<glaubitz@physik.fu-berlin.de> wrote:
>
> 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.
>
> > 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].
>
> I have also CC'ed the debian-powerpc mailing list so that other users can voice their
> opinion.

Note there is no loss of functionality here, at least on radeon
hardware.  It just comes down to which MMU gets used for access to
system memory, the AGP MMU on the chipset or the MMU built into the
GPU.  On powerpc hardware, AGP has been particularly unstable, and
IIRC, AGP has been disabled by default on radeon on powerpc for a
while.

Alex

>
> Thanks,
> Adrian
>
> > [1] https://cdimage.debian.org/cdimage/ports/2020-04-19/
>
> --
>  .''`.  John Paul Adrian Glaubitz
> : :' :  Debian Developer - glaubitz@debian.org
> `. `'   Freie Universitaet Berlin - glaubitz@physik.fu-berlin.de
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