Re: [PATCH 1/2] drm/i915: Use efficient frequency for HSW/BDW

[Daniel Vetter <daniel@ffwll.ch>]

On Wed, Nov 05, 2014 at 05:31:34PM -0800, Tom.O'Rourke@intel.com wrote:
> From: Tom O'Rourke <Tom.O'Rourke@intel.com>
> 
> Updated gen6|8_enable_rps() for Haswell and Broadwell
> to use the efficient frequency read from pcode.
> 
> Added hsw_use_efficient_freq() to read efficient
> frequency (aka RPe) from pcode.  The efficiency is
> based on the frequency/power ratio (MHz/W); this is
> considering GT power and not package power.  The
> efficent frequency is the highest frequency for which
> the frequency/power ratio is within some threshold of
> the highest frequency/power ratio.
> 
> Also set the min_freq_softlimit to the efficient
> frequency.  A fixed decrease in frequency results in
> smaller decrease in power at frequencies less than RPe
> than at frequencies above RPe.
> 
> Signed-off-by: Tom O'Rourke <Tom.O'Rourke@intel.com>
> ---
>  drivers/gpu/drm/i915/i915_reg.h |    1 +
>  drivers/gpu/drm/i915/intel_pm.c |   22 ++++++++++++++++++++++
>  2 files changed, 23 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
> index d43fa0e..6fbfdec 100644
> --- a/drivers/gpu/drm/i915/i915_reg.h
> +++ b/drivers/gpu/drm/i915/i915_reg.h
> @@ -6010,6 +6010,7 @@ enum punit_power_well {
>  #define   GEN6_ENCODE_RC6_VID(mv)		(((mv) - 245) / 5)
>  #define   GEN6_DECODE_RC6_VID(vids)		(((vids) * 5) + 245)
>  #define   DISPLAY_IPS_CONTROL			0x19
> +#define	  HSW_PCODE_DYNAMIC_DUTY_CYCLE_CONTROL	0x1A
>  #define GEN6_PCODE_DATA				0x138128
>  #define   GEN6_PCODE_FREQ_IA_RATIO_SHIFT	8
>  #define   GEN6_PCODE_FREQ_RING_RATIO_SHIFT	16
> diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> index 300d7e5..e4347d9 100644
> --- a/drivers/gpu/drm/i915/intel_pm.c
> +++ b/drivers/gpu/drm/i915/intel_pm.c
> @@ -4706,6 +4706,18 @@ static void parse_rp_state_cap(struct drm_i915_private *dev_priv, u32 rp_state_c
>  		dev_priv->rps.min_freq_softlimit = dev_priv->rps.min_freq;
>  }
>  
> +static void hsw_use_efficient_freq(struct drm_i915_private *dev_priv)
> +{
> +	u32 ddcc_status = 0;
> +	int ret;
> +
> +	ret = sandybridge_pcode_read(dev_priv,
> +					HSW_PCODE_DYNAMIC_DUTY_CYCLE_CONTROL,
> +					&ddcc_status);
> +	if (0 == ret)
> +		dev_priv->rps.efficient_freq = (ddcc_status >> 8) & 0xff;

Control flow in the error case looks funny here - shouldn't we put the
adjustment of the softlimit into the (ret == 0) case here to avoid putting
garbage into it in case the pcode read falls over?

That would make the function name match reality a bit more too, since atm
it just reads the efficient_freq but doesn't use it. So as-is a bit
misnamed.
-Daniel

> +}
> +
>  static void gen9_enable_rps(struct drm_device *dev)
>  {
>  	struct drm_i915_private *dev_priv = dev->dev_private;
> @@ -4765,6 +4777,11 @@ static void gen8_enable_rps(struct drm_device *dev)
>  	rp_state_cap = I915_READ(GEN6_RP_STATE_CAP);
>  	parse_rp_state_cap(dev_priv, rp_state_cap);
>  
> +	if (IS_BROADWELL(dev)) {
> +		hsw_use_efficient_freq(dev_priv);
> +		dev_priv->rps.min_freq_softlimit = dev_priv->rps.efficient_freq;
> +	}
> +
>  	/* 2b: Program RC6 thresholds.*/
>  	I915_WRITE(GEN6_RC6_WAKE_RATE_LIMIT, 40 << 16);
>  	I915_WRITE(GEN6_RC_EVALUATION_INTERVAL, 125000); /* 12500 * 1280ns */
> @@ -4860,6 +4877,11 @@ static void gen6_enable_rps(struct drm_device *dev)
>  
>  	parse_rp_state_cap(dev_priv, rp_state_cap);
>  
> +	if (IS_HASWELL(dev)) {
> +		hsw_use_efficient_freq(dev_priv);
> +		dev_priv->rps.min_freq_softlimit = dev_priv->rps.efficient_freq;
> +	}
> +
>  	/* disable the counters and set deterministic thresholds */
>  	I915_WRITE(GEN6_RC_CONTROL, 0);
>  
> -- 
> 1.7.9.5
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
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