Re: [PATCH] drm/i915: Initialise min/max frequencies before updating RPS registers

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Mon, Aug 26, 2013 at 01:45:56PM +0100, Chris Wilson wrote:
> The RPS register writing routines use the current value of min/max to
> set certain limits and interrupt gating. If we set those afterwards, we
> risk setting up the hw incorrectly and losing power management events,
> and worse, trigger some internal assertions.
> 
> Reorder the calling sequences to be correct, and remove the then
> unrequired clamping from inside set_rps(). And for a bonus, fix the bug
> of calling gen6_set_rps() from Valleyview.
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/i915/i915_debugfs.c |  2 +-
>  drivers/gpu/drm/i915/i915_sysfs.c   | 16 ++++++++--------
>  drivers/gpu/drm/i915/intel_pm.c     | 19 +++++--------------
>  3 files changed, 14 insertions(+), 23 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
> index 2a276c8..b2b1730 100644
> --- a/drivers/gpu/drm/i915/i915_debugfs.c
> +++ b/drivers/gpu/drm/i915/i915_debugfs.c
> @@ -2113,7 +2113,7 @@ i915_max_freq_set(void *data, u64 val)
>  	if (IS_VALLEYVIEW(dev)) {
>  		val = vlv_freq_opcode(dev_priv->mem_freq, val);
>  		dev_priv->rps.max_delay = val;
> -		gen6_set_rps(dev, val);
> +		valleyview_set_rps(dev, val);

Not caused by your patch, but why on earth are we telling the GPU
to switch to the new max_freq here?

In the old way of doing things I presume this should have been
set_rps(cur_delay). And in the new way we should add the 
same 'cur_delay > val' check here that we have in i915_sysfs.

Maybe we should just have some kind of
rps_set_minmax(new_min, new_max) func that takes care of
this stuff in a single location.

>  	} else {
>  		do_div(val, GT_FREQUENCY_MULTIPLIER);
>  		dev_priv->rps.max_delay = val;
> diff --git a/drivers/gpu/drm/i915/i915_sysfs.c b/drivers/gpu/drm/i915/i915_sysfs.c
> index c8c4112..05195c0 100644
> --- a/drivers/gpu/drm/i915/i915_sysfs.c
> +++ b/drivers/gpu/drm/i915/i915_sysfs.c
> @@ -294,15 +294,15 @@ static ssize_t gt_max_freq_mhz_store(struct device *kdev,
>  		DRM_DEBUG("User requested overclocking to %d\n",
>  			  val * GT_FREQUENCY_MULTIPLIER);
>  
> +	dev_priv->rps.max_delay = val;
> +
>  	if (dev_priv->rps.cur_delay > val) {
> -		if (IS_VALLEYVIEW(dev_priv->dev))
> -			valleyview_set_rps(dev_priv->dev, val);
> +		if (IS_VALLEYVIEW(dev))
> +			valleyview_set_rps(dev, val);
>  		else
> -			gen6_set_rps(dev_priv->dev, val);
> +			gen6_set_rps(dev, val);
>  	}
>  
> -	dev_priv->rps.max_delay = val;
> -
>  	mutex_unlock(&dev_priv->rps.hw_lock);
>  
>  	return count;
> @@ -359,15 +359,15 @@ static ssize_t gt_min_freq_mhz_store(struct device *kdev,
>  		return -EINVAL;
>  	}
>  
> +	dev_priv->rps.min_delay = val;
> +
>  	if (dev_priv->rps.cur_delay < val) {
>  		if (IS_VALLEYVIEW(dev))
>  			valleyview_set_rps(dev, val);
>  		else
> -			gen6_set_rps(dev_priv->dev, val);
> +			gen6_set_rps(dev, val);
>  	}
>  
> -	dev_priv->rps.min_delay = val;
> -
>  	mutex_unlock(&dev_priv->rps.hw_lock);
>  
>  	return count;
> diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> index 6767e2b..f995dda 100644
> --- a/drivers/gpu/drm/i915/intel_pm.c
> +++ b/drivers/gpu/drm/i915/intel_pm.c
> @@ -3263,26 +3263,19 @@ static void ironlake_disable_drps(struct drm_device *dev)
>   * ourselves, instead of doing a rmw cycle (which might result in us clearing
>   * all limits and the gpu stuck at whatever frequency it is at atm).
>   */
> -static u32 gen6_rps_limits(struct drm_i915_private *dev_priv, u8 *val)
> +static u32 gen6_rps_limits(struct drm_i915_private *dev_priv, u8 val)
>  {
>  	u32 limits;
>  
> -	limits = 0;
> -
> -	if (*val >= dev_priv->rps.max_delay)
> -		*val = dev_priv->rps.max_delay;
> -	limits |= dev_priv->rps.max_delay << 24;
> -
>  	/* Only set the down limit when we've reached the lowest level to avoid
>  	 * getting more interrupts, otherwise leave this clear. This prevents a
>  	 * race in the hw when coming out of rc6: There's a tiny window where
>  	 * the hw runs at the minimal clock before selecting the desired
>  	 * frequency, if the down threshold expires in that window we will not
>  	 * receive a down interrupt. */
> -	if (*val <= dev_priv->rps.min_delay) {
> -		*val = dev_priv->rps.min_delay;
> +	limits = dev_priv->rps.max_delay << 24;
> +	if (val <= dev_priv->rps.min_delay)
>  		limits |= dev_priv->rps.min_delay << 16;
> -	}
>  
>  	return limits;
>  }
> @@ -3382,7 +3375,6 @@ static void gen6_set_rps_thresholds(struct drm_i915_private *dev_priv, u8 val)
>  void gen6_set_rps(struct drm_device *dev, u8 val)
>  {
>  	struct drm_i915_private *dev_priv = dev->dev_private;
> -	u32 limits = gen6_rps_limits(dev_priv, &val);
>  
>  	WARN_ON(!mutex_is_locked(&dev_priv->rps.hw_lock));
>  	WARN_ON(val > dev_priv->rps.max_delay);
> @@ -3405,7 +3397,8 @@ void gen6_set_rps(struct drm_device *dev, u8 val)
>  	/* Make sure we continue to get interrupts
>  	 * until we hit the minimum or maximum frequencies.
>  	 */
> -	I915_WRITE(GEN6_RP_INTERRUPT_LIMITS, limits);
> +	I915_WRITE(GEN6_RP_INTERRUPT_LIMITS,
> +		   gen6_rps_limits(dev_priv, val));
>  
>  	POSTING_READ(GEN6_RPNSWREQ);
>  
> @@ -3463,8 +3456,6 @@ void valleyview_set_rps(struct drm_device *dev, u8 val)
>  {
>  	struct drm_i915_private *dev_priv = dev->dev_private;
>  
> -	gen6_rps_limits(dev_priv, &val);
> -
>  	WARN_ON(!mutex_is_locked(&dev_priv->rps.hw_lock));
>  	WARN_ON(val > dev_priv->rps.max_delay);
>  	WARN_ON(val < dev_priv->rps.min_delay);
> -- 
> 1.8.4.rc3
> 
> _______________________________________________
> Intel-gfx mailing list
> Intel-gfx@lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/intel-gfx

-- 
Ville Syrjälä
Intel OTC