[Intel-gfx] [PATCH] drm/i915: Acquire RPM wakeref for KMS atomic commit

[Daniel Vetter]

On Sat, Dec 19, 2015 at 09:58:43AM +0000, Chris Wilson wrote:
> Once all the preparations are complete, we are ready to write the
> modesetting to the hardware. During this phase, we will be making lots
> of HW register access, so take a top level wakeref to prevent an
> unwarranted rpm suspend cycle mid-commit. Lower level functions should
> be waking the individual power wells as required.
> 
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=93439
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Imre Deak <imre.deak at intel.com>

The original idea here was that doing this will paper over bugs in our rpm
refcounting. There's also the problem that for modeset stuff we have all
the power wells still to take care of.

For the referenced bug we should add a power domain check in the get hw
state function instead, which is what we've been doing with all the other
similar hw state readout functions too.
-Daniel

> ---
>  drivers/gpu/drm/i915/intel_display.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index abd2d2944022..60451c3932db 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -13470,6 +13470,13 @@ static int intel_atomic_commit(struct drm_device *dev,
>  	drm_atomic_helper_swap_state(dev, state);
>  	dev_priv->wm.config = to_intel_atomic_state(state)->wm_config;
>  
> +	/* Take a rpm wakeref for the duration of the commit. Lower level
> +	 * functions should be acquiring the power wells for their own use,
> +	 * we take this toplevel reference to prevent rpm suspend cycles
> +	 * mid-commit.
> +	 */
> +	intel_runtime_pm_get(dev_priv);
> +
>  	for_each_crtc_in_state(state, crtc, crtc_state, i) {
>  		struct intel_crtc *intel_crtc = to_intel_crtc(crtc);
>  
> @@ -13558,6 +13565,8 @@ static int intel_atomic_commit(struct drm_device *dev,
>  	if (any_ms)
>  		intel_modeset_check_state(dev, state);
>  
> +	intel_runtime_pm_put(dev_priv);
> +
>  	drm_atomic_state_free(state);
>  
>  	return 0;
> -- 
> 2.6.4
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch