Re: [PATCH 4/8] drm/i915: Enable voltage swing before enabling DDI_BUF_CTL.

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

On Tue, Aug 29, 2017 at 04:22:26PM -0700, Rodrigo Vivi wrote:
> Sequences for DisplayPort asks us to
> " Configure voltage swing and related IO settings.
> Refer to DDI Buffer section."
> 
> before "Configure and enable DDI_BUF_CTL"
> 
> On BXT and CNL this means to execute the ddi vswing sequences.
> 
> At this point these sequences calls are getting duplicated for DP
> because they are all called from DP link trainning sequences.
> 
> However this patch is not yet removing it before a futher discussion
> since spec also allows that during link training without disabling
> anything:
> 
> "
> Notes
> Changing voltage swing during link training:
> Change the swing setting following the DDI Buffer section.
> The port does not need to be disabled.
> "
> 
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

Imre is out atm so we didn't get his opinion, but I'm fine with this so
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

> ---
>  drivers/gpu/drm/i915/intel_ddi.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_ddi.c b/drivers/gpu/drm/i915/intel_ddi.c
> index eedd29487e0b..506782c1a62a 100644
> --- a/drivers/gpu/drm/i915/intel_ddi.c
> +++ b/drivers/gpu/drm/i915/intel_ddi.c
> @@ -2136,6 +2136,7 @@ static void intel_ddi_pre_enable_dp(struct intel_encoder *encoder,
>  	struct drm_i915_private *dev_priv = to_i915(encoder->base.dev);
>  	enum port port = intel_ddi_get_encoder_port(encoder);
>  	struct intel_digital_port *dig_port = enc_to_dig_port(&encoder->base);
> +	uint32_t level = intel_ddi_dp_level(intel_dp);
>  
>  	WARN_ON(link_mst && (port == PORT_A || port == PORT_E));
>  
> @@ -2148,7 +2149,11 @@ static void intel_ddi_pre_enable_dp(struct intel_encoder *encoder,
>  
>  	intel_display_power_get(dev_priv, dig_port->ddi_io_power_domain);
>  
> -	if (!IS_GEN9_LP(dev_priv) && !IS_CANNONLAKE(dev_priv))
> +	if (IS_CANNONLAKE(dev_priv))
> +		cnl_ddi_vswing_sequence(encoder, level);
> +	else if (IS_GEN9_LP(dev_priv))
> +		bxt_ddi_vswing_sequence(dev_priv, level, port, encoder->type);
> +	else
>  		intel_prepare_dp_ddi_buffers(encoder);
>  
>  	intel_ddi_init_dp_buf_reg(encoder);
> -- 
> 2.13.2

-- 
Ville Syrjälä
Intel OTC
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