[Intel-gfx] [PATCH 1/3] drm/i915: Use consistent forcewake auto-release timeout across kernel configs

[Chris Wilson]

On Mon, Apr 04, 2016 at 05:51:09PM +0100, Tvrtko Ursulin wrote:
> From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> 
> Current implementation releases the forcewake at any time between
> straight away, and one jiffie from the last put, or first automatic
> grab.

That isn't the problem though. The problem is that we set the timer on
first use rather than last use. All you are stating here is that by
lengthening the timeout on your system you reduce the number of times it
times out.

Having said that, the conversion to hrtimer seems sensible but to add
tracking of the last access as opposed to first we either fallback to
jiffie (in which case hrtimer is moot) or rely on ktime_get_raw() being
fast enough for every register write. Hmm, my usual response to that has
been if it matters we avoid the heavyweight macros and use the _FW
interface - or even raw readl/writel.

Could you try storing ktime_get_raw() on every access and rearming the
timer if it expires before last-access + min-period?
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre