Re: [PATCH 3/6] drm/i915: Optimize the VLV Punit wait a bit

[Daniel Vetter <daniel@ffwll.ch>]

On Tue, Jun 25, 2013 at 07:21:03PM +0300, ville.syrjala@linux.intel.com wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> 
> Don't do needless udelay() calls if the Punit already completed
> the frequency change.
> 
> Also double check things after the timeout to make sure the timeout
> wasn't just caused by some scheduling delays.
> 
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/intel_pm.c | 14 ++++++++++----
>  1 file changed, 10 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> index 6dbcad7..6b98d45 100644
> --- a/drivers/gpu/drm/i915/intel_pm.c
> +++ b/drivers/gpu/drm/i915/intel_pm.c
> @@ -3078,14 +3078,20 @@ static void vlv_update_rps_cur_delay(struct drm_i915_private *dev_priv)
>  
>  	WARN_ON(!mutex_is_locked(&dev_priv->rps.hw_lock));
>  
> -	do {
> -		pval = vlv_punit_read(dev_priv, PUNIT_REG_GPU_FREQ_STS);
> +	pval = vlv_punit_read(dev_priv, PUNIT_REG_GPU_FREQ_STS);
> +
> +	while (pval & 1) {
>  		if (time_after(jiffies, timeout)) {
> -			DRM_DEBUG_DRIVER("timed out waiting for Punit\n");
> +			pval = vlv_punit_read(dev_priv, PUNIT_REG_GPU_FREQ_STS);
>  			break;
>  		}
> +
>  		udelay(10);
> -	} while (pval & 1);
> +		pval = vlv_punit_read(dev_priv, PUNIT_REG_GPU_FREQ_STS);
> +	}
> +
> +	if (pval & 1)
> +		DRM_DEBUG_DRIVER("timed out waiting for Punit\n");

Since we notoriously get these suckers wrong and this check isn't really
in the critical path any more (the punit should have complete the last
change already) and furthermore in a work item: Can we just use one of our
bog-standard wait_for macros here now?
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch