Re: [PATCH 7/9] drm/i915/dp: Implement .set_idle_link_train() for everyone

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

On Mon, Feb 24, 2025 at 07:26:43PM +0200, Ville Syrjala wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> 
> All platforms are capable of explicitly transmitting the idle
> pattern. Implement it for everyone (so far it as implemented
                                                ^was
> only for HSW+).
> 
> The immediate benefit is that we gain support for the
> POST_LT_ADJ_REQ sequence for all platforms.
> 
> Another potential future use would be a pseudo port sync mode on
> pre-BDW where we attempt to sync up multiple ports/pipes by trying
> to turn on the transcoders at the same time, and switching the
> links to normal pixel transmission at the same time.
> 
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/display/g4x_dp.c | 33 +++++++++++++++++++++++++--
>  1 file changed, 31 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/g4x_dp.c b/drivers/gpu/drm/i915/display/g4x_dp.c
> index 372c3683c193..390f9b476a11 100644
> --- a/drivers/gpu/drm/i915/display/g4x_dp.c
> +++ b/drivers/gpu/drm/i915/display/g4x_dp.c
> @@ -621,6 +621,19 @@ cpt_set_link_train(struct intel_dp *intel_dp,
>  	intel_de_posting_read(display, intel_dp->output_reg);
>  }
>  
> +static void
> +cpt_set_idle_link_train(struct intel_dp *intel_dp,
> +			const struct intel_crtc_state *crtc_state)
> +{
> +	struct intel_display *display = to_intel_display(intel_dp);
> +
> +	intel_dp->DP &= ~DP_LINK_TRAIN_MASK_CPT;
> +	intel_dp->DP |= DP_LINK_TRAIN_PAT_IDLE_CPT;
> +
> +	intel_de_write(display, intel_dp->output_reg, intel_dp->DP);
> +	intel_de_posting_read(display, intel_dp->output_reg);
> +}
> +
>  static void
>  g4x_set_link_train(struct intel_dp *intel_dp,
>  		   const struct intel_crtc_state *crtc_state,
> @@ -649,6 +662,19 @@ g4x_set_link_train(struct intel_dp *intel_dp,
>  	intel_de_posting_read(display, intel_dp->output_reg);
>  }
>  
> +static void
> +g4x_set_idle_link_train(struct intel_dp *intel_dp,
> +			const struct intel_crtc_state *crtc_state)
> +{
> +	struct intel_display *display = to_intel_display(intel_dp);
> +
> +	intel_dp->DP &= ~DP_LINK_TRAIN_MASK;
> +	intel_dp->DP |= DP_LINK_TRAIN_PAT_IDLE;
> +
> +	intel_de_write(display, intel_dp->output_reg, intel_dp->DP);
> +	intel_de_posting_read(display, intel_dp->output_reg);
> +}

AFAICS the above could be also used in intel_dp_link_down().

> +
>  static void intel_dp_enable_port(struct intel_dp *intel_dp,
>  				 const struct intel_crtc_state *crtc_state)
>  {
> @@ -1353,10 +1379,13 @@ bool g4x_dp_init(struct intel_display *display,
>  	intel_encoder->audio_disable = g4x_dp_audio_disable;
>  
>  	if ((display->platform.ivybridge && port == PORT_A) ||
> -	    (HAS_PCH_CPT(dev_priv) && port != PORT_A))
> +	    (HAS_PCH_CPT(dev_priv) && port != PORT_A)) {
>  		dig_port->dp.set_link_train = cpt_set_link_train;
> -	else
> +		dig_port->dp.set_idle_link_train = cpt_set_idle_link_train;
> +	} else {
>  		dig_port->dp.set_link_train = g4x_set_link_train;
> +		dig_port->dp.set_idle_link_train = g4x_set_idle_link_train;
> +	}
>  
>  	if (display->platform.cherryview)
>  		intel_encoder->set_signal_levels = chv_set_signal_levels;
> -- 
> 2.45.3
>