[Intel-gfx] [PATCH] drm/i915/guc: Fix a fw content lost issue after it is evicted

[Chris Wilson]

On Fri, Nov 06, 2015 at 03:18:37PM -0800, Yu Dai wrote:
> 
> 
> On 11/06/2015 02:07 PM, Chris Wilson wrote:
> >On Fri, Nov 06, 2015 at 01:55:27PM -0800, yu.dai at intel.com wrote:
> >> From: Alex Dai <yu.dai at intel.com>
> >>
> >> We keep a copy of GuC fw in a GEM obj. However its content is lost
> >> if the GEM obj is evicted (igt/gem_evict_*). Therefore, the later
> >> fw loading during GPU reset will fail.
> >
> >No, it's not. The bug is in sg_copy_buffer called by
> >i915_gem_object_create_from_data introduced by yourselves.
> >
> 
> My understanding is that sg_copy_from_buffer is used to copy data.
> Can you clarify why using this will cause such issue?

"However its content is lost if the GEM obj is evicted (igt/gem_evict_*)."

is not strictly true. The content is lost if the object is swapped
because the page is never marked as dirty. sg_copy_buffer() is copying
into the page but never marks said page as dirty.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre