Re: [PATCH 1/2] drm/i915: use power well count instead of reading hw state when checking status

[Imre Deak <imre.deak@intel.com>]

On Wed, 2014-05-28 at 09:50 -0700, Jesse Barnes wrote:
> This saves many ms per call on my BYT by eliminating Punit communication
> from the hw readout paths.
> 
> Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
> ---
>  drivers/gpu/drm/i915/intel_pm.c | 8 +++-----
>  1 file changed, 3 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> index 452518f..09a3677 100644
> --- a/drivers/gpu/drm/i915/intel_pm.c
> +++ b/drivers/gpu/drm/i915/intel_pm.c
> @@ -5572,13 +5572,11 @@ bool intel_display_power_enabled(struct drm_i915_private *dev_priv,
>  
>  	mutex_lock(&power_domains->lock);
>  	for_each_power_well_rev(i, power_well, BIT(domain), power_domains) {
> -		if (power_well->always_on)
> +		if (power_well->always_on || power_well->count)
>  			continue;
>  
> -		if (!power_well->ops->is_enabled(dev_priv, power_well)) {
> -			is_enabled = false;
> -			break;
> -		}
> +		is_enabled = false;
> +		break;
>  	}
>  	mutex_unlock(&power_domains->lock);

This was meant to return the HW state vs. the state based on the
refcount. It would work in the above way now, because we enable all
power wells for driver init time, but if remove that in the future the
two states may not match.

Perhaps we could maintain a cached version of the HW state in the
power_well struct that we set in the sync_hw handler and update whenever
we turn on/off the wells.

--Imre