Re: [PATCH] drm/i915/bxt: Reversed polarity of PORT_PLL_REF_SEL bit

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

On ke, 2016-03-16 at 18:06 -0700, Dongwon Kim wrote:
> For BXT, description of polarities of PORT_PLL_REF_SEL
> has been reversed for newer Gen9LP steppings according to the
> recent update in Bspec. This bit now should be set for
> "Non-SSC" mode for all Gen9LP starting from B0 stepping.
> 
> v2: Only B0 and newer stepping should be affected by this
> change.

What is this stepping information based on? It's not in BSpec, could
you file a change request to get it added there?

--Imre

> 
> Signed-off-by: Dongwon Kim <dongwon.kim@intel.com>
> ---
>  drivers/gpu/drm/i915/intel_dpll_mgr.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_dpll_mgr.c
> b/drivers/gpu/drm/i915/intel_dpll_mgr.c
> index 4b636c4..c84589e 100644
> --- a/drivers/gpu/drm/i915/intel_dpll_mgr.c
> +++ b/drivers/gpu/drm/i915/intel_dpll_mgr.c
> @@ -1285,7 +1285,15 @@ static void bxt_ddi_pll_enable(struct
> drm_i915_private *dev_priv,
>  	enum port port = (enum port)pll->id;	/* 1:1 port->PLL 
> mapping */
>  
>  	temp = I915_READ(BXT_PORT_PLL_ENABLE(port));
> -	temp &= ~PORT_PLL_REF_SEL;
> +	/*
> +	 * Definition of each bit polarity has been changed
> +	 * after A1 stepping
> +	 */
> +	if (IS_BXT_REVID(dev_priv, 0, BXT_REVID_A1))
> +		temp &= ~PORT_PLL_REF_SEL;
> +	else
> +		temp |= PORT_PLL_REF_SEL;
> +
>  	/* Non-SSC reference */
>  	I915_WRITE(BXT_PORT_PLL_ENABLE(port), temp);
>  
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