linux-kernel - Re: drm/i915: Avoid accessing the stolen address when it is unavailable

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Message-ID: <20131024121706.GB3233@nuc-i3427.alporthouse.com>
Date:	Thu, 24 Oct 2013 13:17:06 +0100
From:	Chris Wilson <chris@...is-wilson.co.uk>
To:	Chuansheng Liu <chuansheng.liu@...el.com>
Cc:	daniel.vetter@...ll.ch, airlied@...ux.ie,
	intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org, fei.li@...el.com
Subject: Re: drm/i915: Avoid accessing the stolen address when it is
 unavailable

On Fri, Oct 25, 2013 at 12:33:47AM +0800, Chuansheng Liu wrote:
> 
> In our platform, we hit the the stolen region initialization failure case,
> such as below log:
> [drm:i915_stolen_to_physical] *ERROR* conflict detected with stolen region: [0x7b000000]
> 
> And it causes the dev_priv->mm.stolen_base is NULL, in this case, we should
> avoid accessing it any more.
> 
> Here is possible call trace:
> intel_enable_gt_powersave -- >
> valleyview_enable_rps -- >
> valleyview_setup_pctx

The two create_stolen routines are no-ops in that case so all that
happens instead is that we read VLV_PCBR. However, really if
i915_gem_object_create_stolen_for_preallocated() fails we should abort
loading the driver as it means we have a hardware conflict and undefined
behaviour.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre
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