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

Roy Spliet nouveau at spliet.org
Tue May 12 20:52:30 UTC 2020

Op 12-05-2020 om 14:36 schreef Alex Deucher:
> 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.

I'll volunteer to be the one asking: how big is this performance 
difference? Have any benchmarks been run before and after removal of AGP 
GART code on affected nouveau/radeon systems? Or is this code being 
dropped _just_ because it's cumbersome, with no regard for metrics that 
determine the value of AGP GART support?


> Alex
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