Re: [PATCH] drm/i915/cnl: Force DDI_A_4_LANES when needed.

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

On Mon, Oct 23, 2017 at 10:12:00AM -0700, Rodrigo Vivi wrote:
> As we faced in BXT, on CNL DDI_A_4_LANES is not
> set as expected when system is boot with multiple
> monitors connected. This result in wrong lane
> setup impacting the max data rate available and
> consequently blocking modeset on eDP, resulting
> in a blank screen.
> 
> Most of CNL SKUs don't support DDI-E.
> The only SKU that supports DDI-E is the same
> that supports the full A/E split called DDI-F.
> 
> Also when DDI-F is used DDI-E cannot be used because
> they share Interrupts. So DDI-E is almost useless.
> Anyways let's consider this is possible and rely on
> VBT for that.
> 
> This patch was initialy start by Clint, but required
> many changes including full commit message. So
> Credits entirely to Clint for finding this.
> 
> v2: Extract all messy conditions into a helper function
>     as suggested by Ville.
>     Along with simplification I removed the debug
>     message on the working case since now all conditions
>     are grouped.
> 
> Suggested-by: Clint Taylor <clinton.a.taylor@intel.com>
> Cc: Clint Taylor <clinton.a.taylor@intel.com>
> Cc: Mika Kahola <mika.kahola@intel.com>
> Cc: Jani Nikula <jani.nikula@intel.com>
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
> ---
>  drivers/gpu/drm/i915/intel_ddi.c | 36 +++++++++++++++++++++++++-----------
>  1 file changed, 25 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_ddi.c b/drivers/gpu/drm/i915/intel_ddi.c
> index adf51b328844..5b03c24bae97 100644
> --- a/drivers/gpu/drm/i915/intel_ddi.c
> +++ b/drivers/gpu/drm/i915/intel_ddi.c
> @@ -2694,6 +2694,24 @@ intel_ddi_init_hdmi_connector(struct intel_digital_port *intel_dig_port)
>  	return connector;
>  }
>  
> +static bool intel_ddi_a_force_4_lanes(struct intel_digital_port *dport)
> +{
> +	struct drm_i915_private *dev_priv = to_i915(dport->base.base.dev);
> +
> +	/* Broxton: Bspec says that DDI_A_4_LANES is the only supported
> +	 *          configuration
> +	 * Cannonlake: Most of SKUs don't support DDI_E, and the only
> +	 *             one who does also have a full A/E split called
> +	 *             DDI_F what makes DDI_E useless. However for this
> +	 *             case let's trust VBT info.
> +	 */
> +	return dport->port == PORT_A &&
> +		!(dport->saved_port_bits & DDI_A_4_LANES) &&
> +		(IS_GEN9_LP(dev_priv) ||
> +		 ((IS_CANNONLAKE(dev_priv)) &&
                  ^                       ^

Those don't look necessary.

It still took me a while to parse that thing. Maybe it should be split
even further? Eg. something like:

{
	if (port != PORT_A)
		return false;
	if (saved_port_bits & 4_LANES)
		return false;

	/* blah */
	if (BXT)
		return true;

	/* meh */
	if (CNL && !port_e_present)
		return true;

	return false;
}

But your code looks correct as well, and I can live with it
if you want to keep it as is. So, with the extra parens removed
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

> +		  !intel_bios_is_port_present(dev_priv, PORT_E)));
> +}
> +
>  void intel_ddi_init(struct drm_i915_private *dev_priv, enum port port)
>  {
>  	struct intel_digital_port *intel_dig_port;
> @@ -2803,18 +2821,14 @@ void intel_ddi_init(struct drm_i915_private *dev_priv, enum port port)
>  	}
>  
>  	/*
> -	 * Bspec says that DDI_A_4_LANES is the only supported configuration
> -	 * for Broxton.  Yet some BIOS fail to set this bit on port A if eDP
> -	 * wasn't lit up at boot.  Force this bit on in our internal
> -	 * configuration so that we use the proper lane count for our
> -	 * calculations.
> +	 * Some BIOS might fail to set this bit on port A if eDP
> +	 * wasn't lit up at boot.  Force this bit set when needed
> +	 * so we use the proper lane count for our calculations.
>  	 */
> -	if (IS_GEN9_LP(dev_priv) && port == PORT_A) {
> -		if (!(intel_dig_port->saved_port_bits & DDI_A_4_LANES)) {
> -			DRM_DEBUG_KMS("BXT BIOS forgot to set DDI_A_4_LANES for port A; fixing\n");
> -			intel_dig_port->saved_port_bits |= DDI_A_4_LANES;
> -			max_lanes = 4;
> -		}
> +	if (intel_ddi_a_force_4_lanes(intel_dig_port)) {
> +		DRM_DEBUG_KMS("Forcing DDI_A_4_LANES for port A\n");
> +		intel_dig_port->saved_port_bits |= DDI_A_4_LANES;
> +		max_lanes = 4;
>  	}
>  
>  	intel_dig_port->max_lanes = max_lanes;
> -- 
> 2.13.5

-- 
Ville Syrjälä
Intel OTC
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