Re: [PATCH 3/7] drm/i915/psr: Make idle_frames sensible again

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

On Wed, May 18, 2016 at 06:47:12PM +0200, Daniel Vetter wrote:
> This reverts
> 
> commit dfaf37baa07513d2c37afff79978807d2d10221a
> Author: Rodrigo Vivi <rodrigo.vivi@intel.com>
> Date:   Mon Dec 7 14:45:20 2015 -0800
> 
>     drm/i915: Fix idle_frames counter.
> 
> and
> 
> commit 97173eaf5f33b1e85efdb06d593d333480b60bf3
> Author: Rodrigo Vivi <rodrigo.vivi@intel.com>
> Date:   Tue Jul 7 16:28:55 2015 -0700
> 
>     drm/i915: PSR: Increase idle_frames
> 
> and implements
> 
> commit d44b4dcbd1b44737462b77971d216d21a9413341
> Author: Rodrigo Vivi <rodrigo.vivi@intel.com>
> Date:   Fri Nov 14 08:52:31 2014 -0800
> 
>     drm/i915: HSW/BDW PSR Set idle_frames = VBT + 1
> 
> without the hack to use 2 idle frames when VBT says 1. We keep the + 1
> just for safety, although I haven't really figured out why that one
> exists.
> 
> It's nonsense. idle_frames = number of frames where the screen is
> entirely idle before we think about entering PSR.
> 
> idle_patter = part of link training, and we probably totally butchered
> link training because we told the hw to entirely skip it. No wonder
> PSR occasionally just fell over.
> 
> I suspect the reason we've increased idle frames is that it makes PSR
> entry slightly less likely, and more likely to happen in a quite
> system, which probably increased the changes the panel came back up
> without link training. The proper fix is to implement link training
> for PSR.

Quite the mess there. At the least this makes things look a bit more
sane.

FWIW
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

> 
> Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
> Cc: Sonika Jindal <sonika.jindal@intel.com>
> Cc: Durgadoss R <durgadoss.r@intel.com>
> Cc: "Pandiyan, Dhinakaran" <dhinakaran.pandiyan@intel.com>
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> ---
>  drivers/gpu/drm/i915/intel_psr.c | 14 +++++++-------
>  1 file changed, 7 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_psr.c b/drivers/gpu/drm/i915/intel_psr.c
> index a788d1e9589b..0295d8dd483f 100644
> --- a/drivers/gpu/drm/i915/intel_psr.c
> +++ b/drivers/gpu/drm/i915/intel_psr.c
> @@ -272,14 +272,14 @@ static void hsw_psr_enable_source(struct intel_dp *intel_dp)
>  	struct drm_i915_private *dev_priv = dev->dev_private;
>  
>  	uint32_t max_sleep_time = 0x1f;
> -	/*
> -	 * Let's respect VBT in case VBT asks a higher idle_frame value.
> -	 * Let's use 6 as the minimum to cover all known cases including
> -	 * the off-by-one issue that HW has in some cases. Also there are
> -	 * cases where sink should be able to train
> -	 * with the 5 or 6 idle patterns.
> +	/* Lately it was identified that depending on panel idle frame count
> +	 * calculated at HW can be off by 1. So let's use what came
> +	 * from VBT + 1.
> +	 * There are also other cases where panel demands at least 4
> +	 * but VBT is not being set. To cover these 2 cases lets use
> +	 * at least 5 when VBT isn't set to be on the safest side.
>  	 */
> -	uint32_t idle_frames = max(6, dev_priv->vbt.psr.idle_frames);
> +	uint32_t idle_frames = dev_priv->vbt.psr.idle_frames + 1;
>  	uint32_t val = EDP_PSR_ENABLE;
>  
>  	val |= max_sleep_time << EDP_PSR_MAX_SLEEP_TIME_SHIFT;
> -- 
> 2.8.1
> 
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-- 
Ville Syrjälä
Intel OTC
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