Re: [PATCH 2/6] drm/i915/psr: Calculate aux less wake time

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

On Thu, Feb 15, 2024 at 12:49:30PM +0200, Jouni Högander wrote:
> Calculate aux less wake time and store it into alpm_params struct
> 
> Bspec: 71477
> 
> Signed-off-by: Jouni Högander <jouni.hogander@intel.com>
> ---
>  .../drm/i915/display/intel_display_types.h    |  1 +
>  drivers/gpu/drm/i915/display/intel_psr.c      | 53 +++++++++++++++++++
>  2 files changed, 54 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_display_types.h b/drivers/gpu/drm/i915/display/intel_display_types.h
> index 0d4012097db1..a531c1e5af20 100644
> --- a/drivers/gpu/drm/i915/display/intel_display_types.h
> +++ b/drivers/gpu/drm/i915/display/intel_display_types.h
> @@ -1721,6 +1721,7 @@ struct intel_psr {
>  
>  		/* LNL and beyond */
>  		u8 check_entry_lines;
> +		u8 aux_less_wake_lines;
>  	} alpm_parameters;
>  
>  	ktime_t last_entry_attempt;
> diff --git a/drivers/gpu/drm/i915/display/intel_psr.c b/drivers/gpu/drm/i915/display/intel_psr.c
> index 72cadad09db5..b139db67df55 100644
> --- a/drivers/gpu/drm/i915/display/intel_psr.c
> +++ b/drivers/gpu/drm/i915/display/intel_psr.c
> @@ -1126,6 +1126,56 @@ static bool _compute_psr2_sdp_prior_scanline_indication(struct intel_dp *intel_d
>  	return true;
>  }
>  
> +/*
> + * AUX-Less Wake Time = CEILING( ((PHY P2 to P0) + tLFPS_Period, Max+
> + * tSilence, Max+ tPHY Establishment + tCDS) / tline)
> + * For the "PHY P2 to P0" latency see the PHY Power Control page
> + * (PHY P2 to P0) : https://gfxspecs.intel.com/Predator/Home/Index/68965
> + * : 12 us
> + * The tLFPS_Period, Max term is 800ns
> + * The tSilence, Max term is 180ns
> + * The tPHY Establishment (a.k.a. t1) term is 50us
> + * The tCDS term is 1 or 2 times t2
> + * t2 = Number ML_PHY_LOCK * tML_PHY_LOCK
> + * Number ML_PHY_LOCK = ( 7 + CEILING( 6.5us / tML_PHY_LOCK ) + 1)
> + * Rounding up the 6.5us padding to the next ML_PHY_LOCK boundary and
> + * adding the "+ 1" term ensures all ML_PHY_LOCK sequences that start
> + * within the CDS period complete within the CDS period regardless of
> + * entry into the period
> + * tML_PHY_LOCK = TPS4 Length * ( 10 / (Link Rate in MHz) )
> + * TPS4 Length = 252 Symbols
> + */
> +static int _lnl_compute_aux_less_wake_time(int port_clock)
> +{
> +	int tml_phy_lock = 1000 * 252 * (10 / port_clock);
> +	int num_ml_phy_lock = 7 + DIV_ROUND_UP(6500, tml_phy_lock) + 1;
> +
> +	return DIV_ROUND_UP(12 * 1000 + 800 + 180 + 50 * 1000 +

Would be much clearer to have a properly named variable for each magic
number. I don't really want to have to read the comment to understand
what the code is calculating.

> +			    num_ml_phy_lock * tml_phy_lock, 1000);
> +}
> +
> +static int _lnl_compute_aux_less_alpm_params(struct intel_dp *intel_dp,
> +					     struct intel_crtc_state *crtc_state)
> +{
> +	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
> +	int aux_less_wake_time, aux_less_wake_lines;
> +
> +	aux_less_wake_time =
> +		_lnl_compute_aux_less_wake_time(crtc_state->port_clock / 1000);
> +	aux_less_wake_lines = intel_usecs_to_scanlines(&crtc_state->hw.adjusted_mode,
> +						       aux_less_wake_time);
> +
> +	if (aux_less_wake_lines > 32)
> +		return false;
> +
> +	if (i915->display.params.psr_safest_params)
> +		aux_less_wake_lines = 32;
> +
> +	intel_dp->psr.alpm_parameters.aux_less_wake_lines = aux_less_wake_lines;
> +
> +	return true;
> +}
> +
>  static bool _lnl_compute_alpm_params(struct intel_dp *intel_dp,
>  				     struct intel_crtc_state *crtc_state)
>  {
> @@ -1142,6 +1192,9 @@ static bool _lnl_compute_alpm_params(struct intel_dp *intel_dp,
>  	if (check_entry_lines > 15)
>  		return false;
>  
> +	if (!_lnl_compute_aux_less_alpm_params(intel_dp, crtc_state))
> +		return false;
> +
>  	if (i915->display.params.psr_safest_params)
>  		check_entry_lines = 15;
>  
> -- 
> 2.34.1

-- 
Ville Syrjälä
Intel