From: "Michel Dänzer" <michel@daenzer•net>
To: Benjamin Herrenschmidt <benh@kernel•crashing.org>
Cc: linuxppc-dev@lists•ozlabs.org,
o jordan <ojordan12345@hotmail•co.uk>,
Andreas Schwab <schwab@linux-m68k•org>
Subject: Re: PowerPC radeon KMS - is it possible?
Date: Wed, 18 Apr 2012 15:27:58 +0200 [thread overview]
Message-ID: <1334755678.5989.320.camel@thor.local> (raw)
In-Reply-To: <1334747877.3143.12.camel@pasglop>
On Mit, 2012-04-18 at 21:17 +1000, Benjamin Herrenschmidt wrote:=20
> On Wed, 2012-04-18 at 12:34 +0200, Michel D=C3=A4nzer wrote:
> > On Mit, 2012-04-18 at 20:20 +1000, Benjamin Herrenschmidt wrote:=20
> > > On Wed, 2012-04-18 at 10:02 +0200, Michel D=C3=A4nzer wrote:
> > > >=20
> > > > > GPU lockup appears to be a common problem with the radeon driver.
> > > >=20
> > > > It's what happens when anything goes wrong with the GPU. If it does=
n't
> > > > happen with agpmode=3D-1, it's probably an AGP related coherency is=
sue.=20
> > >=20
> > > I had some success hacking the DRM to do an in_le32 from the ring hea=
d
> > > after writing it. Just a gross hack but it seemed to help on a G5.
> >=20
> > AFAICT radeon_ring_commit() does that already:
> >=20
> > DRM_MEMORYBARRIER();
> > WREG32(ring->wptr_reg, (ring->wptr << ring->ptr_reg_shift) & ri=
ng->ptr_reg_mask);
> > (void)RREG32(ring->wptr_reg);
> >=20
> > We added the readback about a decade ago. :)
>=20
> Hrm, I have a different hack in that old tree I was playing with a while
> back, let me see...
>=20
> --- a/drivers/gpu/drm/radeon/radeon_cp.c
> +++ b/drivers/gpu/drm/radeon/radeon_cp.c
Note that radeon_cp.c is UMS code, for KMS you need to look at
radeon_ring.c.
> @@ -2245,6 +2245,9 @@ void radeon_commit_ring(drm_radeon_private_t
> *dev_priv)
> DRM_MEMORYBARRIER();
> GET_RING_HEAD( dev_priv );
> =20
> +#ifdef CONFIG_PPC
> + in_be32(dev_priv->ring.start);
> +#endif
> if ((dev_priv->flags & RADEON_FAMILY_MASK) >=3D CHIP_R600) {
>=20
>=20
> I think that my rational was to ensure that all previous stores to
> AGP (indirect buffers etc...) were pushed out & ordered vs the ring
> wptr update or something like that, bcs I think those path aren't well
> ordered in HW. In fact I suspect we might even need a bigger hammer than
> that in_be32().
Probably wouldn't hurt trying something like that in the KMS code as
well.
> Another hack I had around was removing the SBA reset from agp-uninorth
> completely on binding new pages, it seemed to cause hangs.
You mean like commit 5613beb46d54da6ef7f1c4589e9f2e60eeb10721? :)
> > > I suspect there's a fundamental design issue with apple bridge in tha=
t
> > > the CPU to memory path isn't coherent at all with the GPU to memory p=
ath
> > > ie. even vs. cache flush instructions (ie buffers in the memory
> > > controllers can still be out of sync).
> > >=20
> > > Darwin does some gross hacks to work around that, some of them visibl=
e
> > > in the AGP drivers, some burried in the Apple driver, I don't know fo=
r
> > > sure. It's possible that they end up mapping all AGP memory as cache
> > > inhibited, but we can't do that because of our linear mapping.
> >=20
> > We are doing that though...
>=20
> Are we really ? I thought we were taking existing cachable RAM objects
> and mapping them into the AGP gart.
No, the radeon driver has always mapped memory uncacheable to the CPU
while it's bound into the AGP GART.
> Are we replacing both kernel & user mappings for those objects with an
> equivalent cache inhibited mapping ?=20
>=20
> I'm not -that- familiar with how ttm works here.
I'm hardly more familiar with how it all works than you. :)
> In any case it can cause bus checkstops because the same pages can be
> prefetched into the cache via the linear mapping which is covered by
> BATs
So you've been saying for about a decade. :) But I've never seen any
problems tracked down to that.
> (unless you make your graphic objects HIGHMEM only but good luck with
> that :-)
FWIW I think TTM indeed prefers highmem pages for GPU access. The radeon
driver normally doesn't need kernel mappings for them.
--=20
Earthling Michel D=C3=A4nzer | http://www.amd.c=
om
Libre software enthusiast | Debian, X and DRI developer
next prev parent reply other threads:[~2012-04-18 13:28 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-04-17 19:49 PowerPC radeon KMS - is it possible? o jordan
2012-04-18 6:35 ` Michel Dänzer
2012-04-18 6:59 ` Benjamin Herrenschmidt
[not found] ` <1334730915.5989.265.camel__41553.0639271767$1334731329$gmane$org@thor.local>
2012-04-18 7:42 ` Andreas Schwab
2012-04-18 7:52 ` Michel Dänzer
2012-04-18 11:25 ` Andreas Schwab
2012-04-18 13:02 ` Michel Dänzer
2012-04-18 13:22 ` Andreas Schwab
2012-04-18 13:25 ` Michel Dänzer
2012-04-18 13:47 ` Andreas Schwab
2012-04-18 7:54 ` Andreas Schwab
2012-04-18 8:02 ` Michel Dänzer
2012-04-18 10:20 ` Benjamin Herrenschmidt
2012-04-18 10:34 ` Michel Dänzer
2012-04-18 10:44 ` Michel Dänzer
2012-04-18 11:19 ` Benjamin Herrenschmidt
2012-04-18 13:08 ` Michel Dänzer
2012-04-18 12:49 ` Andreas Schwab
2012-04-18 11:17 ` Benjamin Herrenschmidt
2012-04-18 13:27 ` Michel Dänzer [this message]
2012-04-18 11:30 ` Andreas Schwab
2012-04-18 13:38 ` Michel Dänzer
2012-04-18 14:28 ` Andreas Schwab
2012-04-18 14:31 ` Michel Dänzer
2012-04-18 14:55 ` Andreas Schwab
2012-04-18 15:01 ` Michel Dänzer
2012-04-18 15:49 ` Gerhard Pircher
2012-04-18 16:06 ` Michel Dänzer
2012-04-18 16:23 ` Gerhard Pircher
2012-04-19 6:32 ` Michel Dänzer
2012-04-19 11:48 ` Gerhard Pircher
2012-04-19 12:41 ` Michel Dänzer
2012-04-18 15:39 ` Andreas Schwab
[not found] ` <1334732346.1159.5.camel__22339.9641145535$1334732429$gmane$org@pasglop>
2012-04-18 7:46 ` Andreas Schwab
2012-04-18 10:35 ` Benjamin Herrenschmidt
2012-04-18 10:37 ` Benjamin Herrenschmidt
2012-04-18 10:54 ` Michel Dänzer
2012-04-18 11:23 ` Benjamin Herrenschmidt
2012-04-18 13:07 ` Michel Dänzer
2012-04-18 22:25 ` Benjamin Herrenschmidt
-- strict thread matches above, loose matches on Subject: below --
2012-04-20 11:15 Gerhard Pircher
2012-04-20 13:18 ` Michel Dänzer
2012-04-20 16:14 ` Gerhard Pircher
2012-04-23 9:56 ` Michel Dänzer
2012-04-23 16:45 ` Gerhard Pircher
2012-04-24 14:15 ` Michel Dänzer
2012-04-24 17:10 ` Gerhard Pircher
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