[Intel-gfx] force wake reference counting (another try)

[Keith Packard]

On Tue, 12 Apr 2011 18:21:23 +0100, Chris Wilson <chris at chris-wilson.co.uk> wrote:

> Agreed. I had been working under the assumption that dev->struct_mutex was
> the sufficient lock. This may be entirely due to the false premise that we
> only needed i915_gt_read() for the ring registers. I still haven't looked
> through just what registers are impacted.

Seems like we should start using a spinlock and wake lock around all
register accesses, then figure out which registers are not within the GT
power well and split those off to a separate macro which avoids both. If
we finally discover that all wake-lock requiring registers are now
obviously covered by the struct mutex, we could then consider removing
the spinlock.

Make it work, then make it fast.

-- 
keith.packard at intel.com
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