linux-kernel - Re: [ 32/37] drm/i915: correctly order the ring init sequence

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Date:	Fri, 17 Aug 2012 20:29:57 -0300
From:	Herton Ronaldo Krzesinski <herton.krzesinski@...onical.com>
To:	Ben Hutchings <ben@...adent.org.uk>
Cc:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk, Daniel Vetter <daniel.vetter@...ll.ch>,
	Jani Nikula <jani.nikula@...el.com>,
	Yang Guang <guang.a.yang@...el.com>
Subject: Re: [ 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@...ll.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@...el.com>
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=50522
> Tested-by: Yang Guang <guang.a.yang@...el.com>
> Signed-off-by: Daniel Vetter <daniel.vetter@...ll.ch>
> Signed-off-by: Ben Hutchings <ben@...adent.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@...omium.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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