linux-kernel - Re: 3.18-rc regression: drm/nouveau: use shared fences for readable objects

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Message-ID: <546C5085.1020300@canonical.com>
Date:	Wed, 19 Nov 2014 09:10:45 +0100
From:	Maarten Lankhorst <maarten.lankhorst@...onical.com>
To:	Michael Marineau <mike@...ineau.org>,
	dri-devel@...ts.freedesktop.org
CC:	linux-kernel@...r.kernel.org, Ben Skeggs <bskeggs@...hat.com>,
	David Airlie <airlied@...ux.ie>
Subject: Re: 3.18-rc regression: drm/nouveau: use shared fences for readable
 objects

Hey,

On 19-11-14 07:43, Michael Marineau wrote:
> On 3.18-rc kernel's I have been intermittently experiencing GPU
> lockups shortly after startup, accompanied with one or both of the
> following errors:
> 
> nouveau E[   PFIFO][0000:01:00.0] read fault at 0x000734a000 [PTE]
> from PBDMA0/HOST_CPU on channel 0x007faa3000 [unknown]
> nouveau E[     DRM] GPU lockup - switching to software fbcon
> 
> I was able to trace the issue with bisect to commit
> 809e9447b92ffe1346b2d6ec390e212d5307f61c "drm/nouveau: use shared
> fences for readable objects". The lockups appear to have cleared up
> since reverting that and a few related followup commits:
> 
> 809e9447: "drm/nouveau: use shared fences for readable objects"
> 055dffdf: "drm/nouveau: bump driver patchlevel to 1.2.1"
> e3be4c23: "drm/nouveau: specify if interruptible wait is desired in
> nouveau_fence_sync"
> 15a996bb: "drm/nouveau: assign fence_chan->name correctly"

Weird. I'm not sure yet what causes it.

http://cgit.freedesktop.org/~mlankhorst/linux/commit/?h=fixed-fences-for-bisect&id=86be4f216bbb9ea3339843a5658d4c21162c7ee2

On the EDITED patch from fixed-fences-for-bisect, can you do the following:

In nouveau/nv84_fence.c function nv84_fence_context_new, remove

fctx->base.sequence = nv84_fence_read(chan);

and add back

nouveau_bo_wr32(priv->bo, chan->chid * 16/4, 0x00000000);

If that fails you should compile your kernel with trace events, to get some debugging info from the fences. I'll post debugging info if this does not fix it.

~Maarten
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