[Intel-gfx] [PATCH] drm/i915: Request for resets under forcewake

[Chris Wilson]

On Wed, Nov 04, 2015 at 11:33:04AM +0200, Mika Kuoppala wrote:
> We have a timed release of a forcewake when using
> I915_READ/WRITE macros. wait_for() macro will go to quite
> long sleep if the first read doesn't satisfy the condition for
> successful exit. With these two interacting, it is possible that
> we lose the forcewake during the wait_for() and the subsequent read
> will reaquire forcewake.
> 
> Further experiments with skl shows that when we lose forcewake,
> we lose the reset request we submitted. So this register
> is not power context saved.
> 
> Grab forcewakes for all engines before starting to request for
> resets so that all requests stay valid for the duration of reset
> requisition across all the engines.
> 
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=92774
> Cc: Chris Wilson <chris at chris-wilson.co.uk>
> Tested-by: Tomi Sarvela <tomix.p.sarvela at intel.com>
> Signed-off-by: Mika Kuoppala <mika.kuoppala at intel.com>
> ---
>  drivers/gpu/drm/i915/intel_uncore.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c
> index f0f97b2..5a6e7f1b 100644
> --- a/drivers/gpu/drm/i915/intel_uncore.c
> +++ b/drivers/gpu/drm/i915/intel_uncore.c
> @@ -1483,6 +1483,8 @@ static int gen8_do_reset(struct drm_device *dev)
>  	struct intel_engine_cs *engine;
>  	int i;
>  
        /* If the power well sleeps during the reset, the reset
	 * request may be dropped and never completes (causing -EIO).
	 */
> +	intel_uncore_forcewake_get(dev_priv, FORCEWAKE_ALL);

I wonder if this would be more useful in intel_gpu_reset(), it won't
hurt any other platforms and may prevent similar snafu in future?
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre