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SubjectRe: [ 32/37] drm/i915: correctly order the ring init sequence
On Fri, Aug 17, 2012 at 04:03:15AM +0100, Ben Hutchings wrote:
> 3.2-stable review patch. If anyone has any objections, please let me know.
>
> ------------------
>
> From: Daniel Vetter <daniel.vetter@ffwll.ch>
>
> commit 0d8957c8a90bbb5d34fab9a304459448a5131e06 upstream.
>
> We may only start to set up the new register values after having
> confirmed that the ring is truely off. Otherwise the hw might lose the
> newly written register values. This is caught later on in the init
> sequence, when we check whether the register writes have stuck.
>
> Reviewed-by: Jani Nikula <jani.nikula@intel.com>
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=50522
> Tested-by: Yang Guang <guang.a.yang@intel.com>
> Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
[...]

With this commit on 3.2, i915 fails to initialize on a G41 based machine
I have here:

[ 36.894261] i915 0000:00:02.0: PCI INT A -> GSI 16 (level, low) -> IRQ 16
[ 36.894265] i915 0000:00:02.0: setting latency timer to 64
[ 36.933118] mtrr: type mismatch for d0000000,10000000 old: write-back new: write-combining
[ 36.933121] [drm] MTRR allocation failed. Graphics performance may suffer.
[ 36.933467] i915 0000:00:02.0: irq 42 for MSI/MSI-X
[ 36.933471] [drm] Supports vblank timestamp caching Rev 1 (10.10.2010).
[ 36.933472] [drm] Driver supports precise vblank timestamp query.
[ 36.933498] vgaarb: device changed decodes: PCI:0000:00:02.0,olddecodes=io+mem,decodes=io+mem:owns=io+mem
[ 36.969669] [drm:init_ring_common] *ERROR* render ring initialization failed ctl 0001f001 head 00001074 tail 00000000 start 00001000
[ 36.969763] vga_switcheroo: disabled
[ 36.969765] [drm:i915_driver_load] *ERROR* failed to init modeset
[ 36.987444] i915 0000:00:02.0: PCI INT A disabled
[ 36.987453] i915: probe of 0000:00:02.0 failed with error -5

Taking a look at it, I suspected of a timing issue, especially looking at
this commit, which isn't on 3.2:

commit f01db988ef6f6c70a6cc36ee71e4a98a68901229
Author: Sean Paul <seanpaul@chromium.org>
Date: Fri Mar 16 12:43:22 2012 -0400

drm/i915: Add wait_for in init_ring_common

And picking it made the issue go away, so the extra delay helped and is needed
with 0d8957c8a90bbb5d34fab9a304459448a5131e06 applied here.

--
[]'s
Herton


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