Re: [PATCH v4 2/2] drm/i915/vlv: WA to fix Voltage not getting dropped to Vmin when Gfx is power gated.

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

On Mon, Jan 27, 2014 at 09:35:06PM +0530, deepak.s@intel.com wrote:
> From: Deepak S <deepak.s@intel.com>
> 
> When we enter RC6 and GFX Clocks are off, the voltage remains higher
> than Vmin. When we try to set the freq to RPn, it might fail since the
> Gfx clocks are down. So to fix this in Gfx idle, Bring the GFX clock up
> and set the freq to RPn then move GFx down.
> 
> v2: remove vlv_update_rps_cur_delay function. Update commit message (Daniel)
> 
> v3: Fix the timeout during wait for gfx clock (Jesse)
> 
> v4: addressed comments on set freq and punit wait (Ville)
> 
> Signed-off-by: Deepak S <deepak.s@intel.com>
> ---
>  drivers/gpu/drm/i915/i915_reg.h |  4 ++++
>  drivers/gpu/drm/i915/intel_pm.c | 53 ++++++++++++++++++++++++++++++++++++++++-
>  2 files changed, 56 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
> index 242f540..feaa83b 100644
> --- a/drivers/gpu/drm/i915/i915_reg.h
> +++ b/drivers/gpu/drm/i915/i915_reg.h
> @@ -4944,6 +4944,10 @@
>  						 GEN6_PM_RP_DOWN_THRESHOLD | \
>  						 GEN6_PM_RP_DOWN_TIMEOUT)
>  
> +#define VLV_GTLC_SURVIVABILITY_REG              0x130098
> +#define VLV_GFX_CLK_STATUS_BIT			(1<<3)
> +#define VLV_GFX_CLK_FORCE_ON_BIT		(1<<2)
> +
>  #define GEN6_GT_GFX_RC6_LOCKED			0x138104
>  #define VLV_COUNTER_CONTROL			0x138104
>  #define   VLV_COUNT_RANGE_HIGH			(1<<15)
> diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> index c6a07c9..84e20d0 100644
> --- a/drivers/gpu/drm/i915/intel_pm.c
> +++ b/drivers/gpu/drm/i915/intel_pm.c
> @@ -3035,6 +3035,56 @@ void gen6_set_rps(struct drm_device *dev, u8 val)
>  	trace_intel_gpu_freq_change(val * 50);
>  }
>  
> +/* vlv_set_rps_idle: Set the frequency to Rpn if Gfx clocks are down
> + *
> + * * If Gfx is Idle, then
> + * 1. Mask Turbo interrupts
> + * 2. Bring up Gfx clock
> + * 3. Change the freq to Rpn and wait till P-Unit updates freq
> + * 4. Clear the Force GFX CLK ON bit so that Gfx can down
> + * 5. Unmask Turbo interrupts
> +*/
> +static void vlv_set_rps_idle(struct drm_i915_private *dev_priv)
> +{
> +	/*
> +	 * When we are idle.  Drop to min voltage state.
> +	 */
> +
> +	if (dev_priv->rps.cur_delay <= dev_priv->rps.min_delay)
> +		return;

If we're already at min freq I guess there's a good chance we're at the
min voltage too. But I'm not sure that's really guaranteed by anything.
Maybe it's enough. If not then I guess we should track whether we've
already called this function w/o going to higher voltage in between.

> +
> +	/* Mask turbo interrupt so that they will not come in between */
> +	I915_WRITE(GEN6_PMINTRMSK, 0xffffffff);
> +
> +	/* Bring up the Gfx clock */
> +	I915_WRITE(VLV_GTLC_SURVIVABILITY_REG,
> +		I915_READ(VLV_GTLC_SURVIVABILITY_REG) |
> +				VLV_GFX_CLK_FORCE_ON_BIT);
> +
> +	if (wait_for_atomic(((VLV_GFX_CLK_STATUS_BIT &
> +		I915_READ(VLV_GTLC_SURVIVABILITY_REG)) != 0), 5)) {
> +			DRM_ERROR("GFX_CLK_ON request timed out\n");
> +		return;
> +	}
> +
> +	vlv_punit_write(dev_priv, PUNIT_REG_GPU_FREQ_REQ, dev_priv->rps.min_delay);

We should update cur_delay to reflect this.

> +
> +	if (wait_for_atomic(((vlv_punit_read(dev_priv, PUNIT_REG_GPU_FREQ_STS))
> +				& GENFREQSTATUS) == 0, 5))
> +		DRM_DEBUG_DRIVER("timed out waiting for Punit\n");
> +
> +	/* Release the Gfx clock */
> +	I915_WRITE(VLV_GTLC_SURVIVABILITY_REG,
> +		I915_READ(VLV_GTLC_SURVIVABILITY_REG) &
> +				~VLV_GFX_CLK_FORCE_ON_BIT);
> +
> +	/* Unmask Turbo interrupts */
> +	I915_WRITE(GEN6_PMINTRMSK, ~(GEN6_PM_RPS_EVENTS |
> +					GEN6_PM_RP_UP_EI_EXPIRED));

Wouldn't that confuse the interrupt masking logic you just introduced
in the previous patch?

So looks to me like pretending we got a down threshold interrupt here
is all that's needed to keep things in sync. So somehting like:
gen6_set_pm_mask(dev_priv, GEN6_PM_RP_DOWN_THRESHOLD, min_delay);

> +}
> +
> +
> +
>  void gen6_rps_idle(struct drm_i915_private *dev_priv)
>  {
>  	struct drm_device *dev = dev_priv->dev;
> @@ -3042,7 +3092,7 @@ void gen6_rps_idle(struct drm_i915_private *dev_priv)
>  	mutex_lock(&dev_priv->rps.hw_lock);
>  	if (dev_priv->rps.enabled) {
>  		if (IS_VALLEYVIEW(dev))
> -			valleyview_set_rps(dev_priv->dev, dev_priv->rps.min_delay);
> +			vlv_set_rps_idle(dev_priv);
>  		else
>  			gen6_set_rps(dev_priv->dev, dev_priv->rps.min_delay);
>  		dev_priv->rps.last_adj = 0;
> @@ -4273,6 +4323,7 @@ void intel_gpu_ips_teardown(void)
>  	i915_mch_dev = NULL;
>  	spin_unlock_irq(&mchdev_lock);
>  }
> +
>  static void intel_init_emon(struct drm_device *dev)
>  {
>  	struct drm_i915_private *dev_priv = dev->dev_private;
> -- 
> 1.8.5.2
> 
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-- 
Ville Syrjälä
Intel OTC