Re: [PATCH 10/10] drm/i915/cnl: Fix DP max rate for Cannonlake with port F.

[Jani Nikula <jani.nikula@linux.intel.com>]

On Mon, 29 Jan 2018, Rodrigo Vivi <rodrigo.vivi@intel.com> wrote:
> On CNL SKUs that uses port F,  max DP rate is 8.1G for all
> ports when we have the elevated voltage (higher than 0.85V).
>
> v2: Make commit message more generic.
> v3: Move conditions to a helper to get easier to read. (Ville).
> v4: Add a mention to the numerical voltage on commit
>     message per Manasi request.
> v5: Thanks CI! "error: control reaches end of non-void function"
>
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Cc: Lucas De Marchi <lucas.demarchi@intel.com>
> Cc: Manasi Navare <manasi.d.navare@intel.com>
> Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
> Reviewed-by: Manasi Navare <manasi.d.navare@intel.com>
> ---
>  drivers/gpu/drm/i915/intel_dp.c | 31 ++++++++++++++++++++++++-------
>  1 file changed, 24 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index 86a5e8bfe2a6..1f10bdb855e7 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -220,15 +220,36 @@ intel_dp_downstream_max_dotclock(struct intel_dp *intel_dp)
>  	return max_dotclk;
>  }
>  
> +static int cnl_adjusted_max_rate(struct intel_dp *intel_dp, int size)
> +{
> +	struct intel_digital_port *dig_port = dp_to_dig_port(intel_dp);
> +	struct drm_i915_private *dev_priv = to_i915(dig_port->base.base.dev);
> +	enum port port = dig_port->base.port;
> +
> +	u32 voltage = I915_READ(CNL_PORT_COMP_DW3) & VOLTAGE_INFO_MASK;
> +
> +	/* Low voltage SKUs are limited to max of 5.4G */
> +	if (voltage == VOLTAGE_INFO_0_85V)
> +		return size - 2;
> +
> +	/* For this SKU 8.1G is supported in all ports */
> +	if(IS_CNL_WITH_PORT_F(dev_priv))
> +		return size;
> +
> +	/* For other SKUs, max rate on ports A and B is 5.4G */
> +	if (port == PORT_A || port == PORT_D)
> +		return size - 2;
> +
> +	return size;

IMO this splits the ARRAY_SIZE() and the (size - 2) adjustments too
much. They were tolerable within one function, but looking at this
function alone, the (size - 2) is a big WTF.

I'd just put this all in the same function.

BR,
Jani.


> +}
> +
>  static void
>  intel_dp_set_source_rates(struct intel_dp *intel_dp)
>  {
>  	struct intel_digital_port *dig_port = dp_to_dig_port(intel_dp);
>  	struct drm_i915_private *dev_priv = to_i915(dig_port->base.base.dev);
> -	enum port port = dig_port->base.port;
>  	const int *source_rates;
>  	int size;
> -	u32 voltage;
>  
>  	/* This should only be done once */
>  	WARN_ON(intel_dp->source_rates || intel_dp->num_source_rates);
> @@ -238,11 +259,7 @@ intel_dp_set_source_rates(struct intel_dp *intel_dp)
>  		size = ARRAY_SIZE(bxt_rates);
>  	} else if (IS_CANNONLAKE(dev_priv)) {
>  		source_rates = cnl_rates;
> -		size = ARRAY_SIZE(cnl_rates);
> -		voltage = I915_READ(CNL_PORT_COMP_DW3) & VOLTAGE_INFO_MASK;
> -		if (port == PORT_A || port == PORT_D ||
> -		    voltage == VOLTAGE_INFO_0_85V)
> -			size -= 2;
> +		size = cnl_adjusted_max_rate(intel_dp, ARRAY_SIZE(cnl_rates));
>  	} else if (IS_GEN9_BC(dev_priv)) {
>  		source_rates = skl_rates;
>  		size = ARRAY_SIZE(skl_rates);

-- 
Jani Nikula, Intel Open Source Technology Center
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