Re: [PATCH 06/14] drm/i915: Fix LP1+ watermark disabling ILK

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

On Thu, 2013-12-05 at 15:51 +0200, ville.syrjala@linux.intel.com wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> 
> On ILK disabling LP1+ watermarks must be done carefully to avoid
> underruns. If we just write 0 to the register in the middle of the scan
> cycle we often get an underrun. So instead we have to leave the actual
> watermark levels in the register intact, and just toggle the enable bit.
> 
> Presumably the hardware takes a while to get out of low power mode, and
> so the watermark level need to stay valid until that time.
> 
> We also have to be careful with the WM1S_LP_EN bit. It seems the
> hardware more or less treats it like the actual watermarks numbers, and
> so we must not toggle it too soon. Just leave it alone when disabling
> the LP1+ watermarks.
> 
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/intel_pm.c | 33 ++++++++++++++++++++-------------
>  1 file changed, 20 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> index db7f3a6..1aa6ea9 100644
> --- a/drivers/gpu/drm/i915/intel_pm.c
> +++ b/drivers/gpu/drm/i915/intel_pm.c
> @@ -2897,16 +2897,23 @@ static void hsw_write_wm_values(struct drm_i915_private *dev_priv,
>  	if (!dirty)
>  		return;
>  
> -	if (dirty & WM_DIRTY_LP(3) && previous->wm_lp[2] != 0)
> -		I915_WRITE(WM3_LP_ILK, 0);
> -	if (dirty & WM_DIRTY_LP(2) && previous->wm_lp[1] != 0)
> -		I915_WRITE(WM2_LP_ILK, 0);
> -	if (dirty & WM_DIRTY_LP(1) && previous->wm_lp[0] != 0)
> -		I915_WRITE(WM1_LP_ILK, 0);
> +	if (dirty & WM_DIRTY_LP(3) && previous->wm_lp[2] & WM1_LP_SR_EN) {
> +		previous->wm_lp[2] &= ~WM1_LP_SR_EN;
> +		I915_WRITE(WM3_LP_ILK, previous->wm_lp[2]);
> +	}
> +	if (dirty & WM_DIRTY_LP(2) && previous->wm_lp[1] & WM1_LP_SR_EN) {
> +		previous->wm_lp[1] &= ~WM1_LP_SR_EN;
> +		I915_WRITE(WM2_LP_ILK, previous->wm_lp[1]);
> +	}
> +	if (dirty & WM_DIRTY_LP(1) && previous->wm_lp[0] & WM1_LP_SR_EN) {
> +		previous->wm_lp[0] &= ~WM1_LP_SR_EN;
> +		I915_WRITE(WM1_LP_ILK, previous->wm_lp[0]);
> +	}
>  
> -	if (INTEL_INFO(dev)->gen <= 6 &&
> -	    dirty & WM_DIRTY_LP(1) && previous->wm_lp_spr[0] != 0)
> -		I915_WRITE(WM1S_LP_ILK, 0);
> +	/*
> +	 * Don't touch WM1S_LP_EN here.
> +	 * Doing so could cause underruns.
> +	 */
>  
>  	if (dirty & WM_DIRTY_PIPE(PIPE_A))
>  		I915_WRITE(WM0_PIPEA_ILK, results->wm_pipe[0]);
> @@ -2950,7 +2957,7 @@ static void hsw_write_wm_values(struct drm_i915_private *dev_priv,
>  	}
>  
>  	if (INTEL_INFO(dev)->gen <= 6) {
> -		if (dirty & WM_DIRTY_LP(1) && results->wm_lp_spr[0] != 0)
> +		if (dirty & WM_DIRTY_LP(1) && previous->wm_lp_spr[0] != results->wm_lp_spr[0])
>  			I915_WRITE(WM1S_LP_ILK, results->wm_lp_spr[0]);

This and the below "else" version are the same now, so it could be moved
before the if.

--Imre

>  	} else {
>  		if (dirty & WM_DIRTY_LP(1) && previous->wm_lp_spr[0] != results->wm_lp_spr[0])



> @@ -2961,11 +2968,11 @@ static void hsw_write_wm_values(struct drm_i915_private *dev_priv,
>  			I915_WRITE(WM3S_LP_IVB, results->wm_lp_spr[2]);
>  	}
>  
> -	if (dirty & WM_DIRTY_LP(1) && results->wm_lp[0] != 0)
> +	if (dirty & WM_DIRTY_LP(1) && previous->wm_lp[0] != results->wm_lp[0])
>  		I915_WRITE(WM1_LP_ILK, results->wm_lp[0]);
> -	if (dirty & WM_DIRTY_LP(2) && results->wm_lp[1] != 0)
> +	if (dirty & WM_DIRTY_LP(2) && previous->wm_lp[1] != results->wm_lp[1])
>  		I915_WRITE(WM2_LP_ILK, results->wm_lp[1]);
> -	if (dirty & WM_DIRTY_LP(3) && results->wm_lp[2] != 0)
> +	if (dirty & WM_DIRTY_LP(3) && previous->wm_lp[2] != results->wm_lp[2])
>  		I915_WRITE(WM3_LP_ILK, results->wm_lp[2]);
>  
>  	dev_priv->wm.hw = *results;


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