[PATCH 1/3] drm/radeon: remove AGP support

[Émeric MASCHINO]

> On Tue, May 12, 2020 at 4:16 AM Michel Dänzer <michel at daenzer.net> wrote:
> >
> > On 2020-05-11 10:12 p.m., Alex Deucher wrote:
> > > On Mon, May 11, 2020 at 1:17 PM Christian König
> > > <ckoenig.leichtzumerken at gmail.com> wrote:
> > >>
> > >> AGP is deprecated for 10+ years now and not used any more on modern hardware.
> > >>
> > >> Old hardware should continue to work in PCI mode.
> > >
> > > Might want to clarify that there is no loss of functionality here.
> > > Something like:
> > >
> > > "There is no loss of functionality here.  GPUs will continue to
> > > function.  This just drops the use of the AGP MMU in the chipset in
> > > favor of the MMU on the device which has proven to be much more
> > > reliable.  Due to its unreliability, AGP support has been disabled on
> > > PowerPC for years already so there is no change on PowerPC."
> >
> > There's a difference between something being disabled by default or not
> > being available at all. We may decide it's worth it anyway, but let's do
> > it based on facts.
> >
>
> I didn't mean to imply that AGP GART support was already removed.  But
> for the vast majority of users the end result is the same.  If you
> knew enough re-enable AGP GART, you probably wouldn't have been as
> confused about what this patch set does either.  To reiterate, this
> patch set does not remove support for AGP cards, it only removes the
> support for AGP GART.  The cards will still be functional using the
> device GART.  There may be performance tradeoffs there in some cases.
>
> Alex

Back in the fglrx days, the fglrxconfig utility proposed:


==============================================================================
Advanced OS Settings
==============================================================================

External AGPGART module:

It is possible (but not recommended) to turn off the usage of
built-in agp support of the provided fglrx kernel module and
use the external AGP GART module (agpgart.o) of the Linux kernel.
If you want to use the external module then ensure that it loads
prior to the drivers full startup. In order to manually load the
external agpgart module execute this on the commandline (as root):
/sbin/insmod agpgart
or alternatively configure your system to auto load the module.

Do you want to use the external AGP GART module (y/n)? [n]


By "built-in agp support of the provided fglrx kernel module", was
fglrxconfig referring to the "device GART"? So the device-side IOMMU
allowing to "work in PCI mode", somewhat dubbed as "PCI GART" (even
for AGP graphics adapters?!??) in some messages here?

If so, it is noteworthy that the default choice was not to use the
external AGP GART (resulting in Option "UseInternalAGPGART" "yes" in
/etc/X11/XF86Config), thus leveraging the device GART, i.e. what
Christian proposal is all about. Unless I still mix everything.

     Émeric