From: Alex Deucher <alexdeucher@gmail.com>
To: Daniel Vetter <daniel@ffwll.ch>
Cc: "Christian König" <ckoenig.leichtzumerken@gmail.com>,
"Michel Dänzer" <michel@daenzer.net>,
"Maling list - DRI developers" <dri-devel@lists.freedesktop.org>,
"Rui Salvaterra" <rsalvaterra@gmail.com>,
"debian-powerpc@lists.debian.org"
<debian-powerpc@lists.debian.org>,
"John Paul Adrian Glaubitz" <glaubitz@physik.fu-berlin.de>,
"Karoly Balogh (Charlie/SGR)" <charlie@scenergy.dfmk.hu>
Subject: Re: [RFC] Remove AGP support from Radeon/Nouveau/TTM
Date: Tue, 12 May 2020 14:22:40 -0400 [thread overview]
Message-ID: <CADnq5_NFDjOzgnjHOHEcjacd2dX1kA1QEzHp8=NweZg_b-82-A@mail.gmail.com> (raw)
In-Reply-To: <CAKMK7uG3R4uve41MkkcFSiDJ+p=MwW81gcFW7NFENjKbdDUZ+g@mail.gmail.com>
On Tue, May 12, 2020 at 12:38 PM Daniel Vetter <daniel@ffwll.ch> wrote:
>
> On Tue, May 12, 2020 at 3:22 PM Alex Deucher <alexdeucher@gmail.com> wrote:
> >
> > On Tue, May 12, 2020 at 5:40 AM Karoly Balogh (Charlie/SGR)
> > <charlie@scenergy.dfmk.hu> wrote:
> > >
> > > Hi,
> > >
> > > On Tue, 12 May 2020, Rui Salvaterra wrote:
> > >
> > > > > FWIW, on my last-generation PowerBook with RV350 (IIRC), there was a
> > > > > big performance difference between AGP and PCI GART. The latter was
> > > > > sort of usable for normal desktop operation, but not so much for
> > > > > OpenGL apps (which were usable with AGP).
> > > >
> > > > I never really understood what were the issues with AGP on PowerPC
> > > > (well, Apple, the only ones I've tested) machines. I mean, did OS X also
> > > > disable AGP entirely, or did it have workarounds somewhere else on the
> > > > stack nobody was able to figure out?
> > >
> > > I don't know about OS X, but I doubt there is a major/blocker hardware
> > > issue, at least not one which affects every AGP machine.
> > >
> > > MorphOS' own Radeon driver uses the AGP facilities to some degree on all
> > > AGP PowerPC Macs supported by that OS, which is from PMac AGP Graphics
> > > (3,1) all the way up to the AGP G5 (7,3), including the various portables
> > > and the Mac mini G4. For example it can utilize it to stream video data
> > > directly from mainboard RAM, so you don't have to copy it with the CPU,
> > > allowing reasonably good 720p h264 video playback on most systems above
> > > the 1Ghz mark with the native MPlayer port. I'm sure the 3D part of the
> > > driver also use it to some degree, given the performance improvement we
> > > experienced when the AGP support was enabled (initially the system was
> > > running without it), but to which extent I can't say.
> >
> > The problem is AGP doesn't support CPU cache snooping. Technically
> > PCI must support coherent device access to system memory. Unsnooped
> > access is an optional feature and some platforms may not support it at
> > all. Unfortunately, AGP required unsnooped access. x8t generally
> > provides a way to do this, but other platforms, not so much. I don't
> > recall to what extent PowerPC supported this. The Linux DMA API
> > doesn't really have a way to get uncached memory for DMA so there is
> > that too. Windows and Mac may provide a way to do this depending on
> > the platforms. What probably should have been done on AGP boards was
> > to use both the AGP GART and the device GART. The former for uncached
> > memory (if the platform supported it) and the latter for cached
> > memory. That never happened.
>
> Slight correction on the dma-api side of things: The dma-api very much
> can give you uncached memory, but only on some platforms, and the
> dma-api is very opinionated about which those are. And it refuses to
> tell you whether your memory ends up being uncached or cached. That's
> all done in the name of platform portability, which is good for most
> drivers, but just too much pain for gpu drivers.
Out of curiosity how do you do that without manually messing around
with PAT or MTRRs?
Alex
>
> Otherwise all agree, agp is a mighty mess and essentially just
> crapshot outside of x86. It kinda worked for the much more static
> allocations for dri1, but with in-kernel memory managers all the cache
> flushing issues showed up big time and it all fell to pieces. Plus a
> lot of these host chipset back then where designed for the rather
> static windows gpu managers, so even on x86 the coherency issues for
> agp mode when used together with ttm or something else really dynamic
> is pretty bad because the hw just doesn't really cope and has all
> kinds of flushing troubles and races. I think the later agp chipsets
> were better.
> -Daniel
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> +41 (0) 79 365 57 48 - http://blog.ffwll.ch
_______________________________________________
dri-devel mailing list
dri-devel@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/dri-devel
next prev parent reply other threads:[~2020-05-12 18:22 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-11 19:55 [RFC] Remove AGP support from Radeon/Nouveau/TTM John Paul Adrian Glaubitz
2020-05-11 20:05 ` Alex Deucher
2020-05-11 20:25 ` Rui Salvaterra
2020-05-11 20:51 ` Alex Deucher
2020-05-12 7:57 ` Michel Dänzer
2020-05-12 9:21 ` Rui Salvaterra
2020-05-12 9:40 ` Karoly Balogh (Charlie/SGR)
2020-05-12 13:22 ` Alex Deucher
2020-05-12 16:37 ` Daniel Vetter
2020-05-12 17:02 ` Rui Salvaterra
2020-05-12 18:21 ` Alex Deucher
2020-05-12 20:12 ` Dave Airlie
2020-05-13 7:26 ` Christian König
2020-05-12 18:22 ` Alex Deucher [this message]
2020-05-13 7:19 ` Daniel Vetter
2020-05-13 7:55 ` Christian König
2020-05-13 10:25 ` Daniel Vetter
2020-05-13 9:28 ` Rui Salvaterra
2020-05-13 10:26 ` Michel Dänzer
2020-05-13 10:29 ` Daniel Vetter
2020-05-13 10:32 ` Michel Dänzer
2020-05-13 10:39 ` Rui Salvaterra
2020-05-13 10:57 ` Michel Dänzer
2020-05-13 11:07 ` Rui Salvaterra
2020-05-13 13:44 ` Christian Zigotzky
2020-05-13 14:01 ` John Paul Adrian Glaubitz
2020-05-13 14:01 ` Rui Salvaterra
2020-05-13 20:19 ` Bertrand Dekoninck
2020-05-13 20:36 ` Rui Salvaterra
2020-05-11 20:41 ` John Paul Adrian Glaubitz
2020-05-11 20:46 ` Alex Deucher
2020-05-11 21:50 ` John Paul Adrian Glaubitz
2020-05-12 7:43 ` Christian König
2020-05-11 20:12 ` Christian König
2020-05-11 20:24 ` John Paul Adrian Glaubitz
2020-05-11 20:48 ` Gerhard Pircher
2020-05-12 5:04 ` David VANTYGHEM
2020-05-12 9:20 ` John Paul Adrian Glaubitz
-- strict thread matches above, loose matches on Subject: below --
2020-05-11 17:17 Christian König
2020-05-11 20:14 ` Al Dunsmuir
2020-05-11 20:27 ` Alex Deucher
2020-05-11 20:43 ` Dave Airlie
2020-05-11 20:56 ` Al Dunsmuir
2020-05-12 8:11 ` Christian König
2020-05-11 20:59 ` Emil Velikov
2020-05-11 20:46 ` Al Dunsmuir
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to='CADnq5_NFDjOzgnjHOHEcjacd2dX1kA1QEzHp8=NweZg_b-82-A@mail.gmail.com' \
--to=alexdeucher@gmail.com \
--cc=charlie@scenergy.dfmk.hu \
--cc=ckoenig.leichtzumerken@gmail.com \
--cc=daniel@ffwll.ch \
--cc=debian-powerpc@lists.debian.org \
--cc=dri-devel@lists.freedesktop.org \
--cc=glaubitz@physik.fu-berlin.de \
--cc=michel@daenzer.net \
--cc=rsalvaterra@gmail.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).