Re: Thinkpad T420 and single/dual channel lvds

[Adam Jackson <ajax@redhat.com>]

On 3/15/12 10:42 AM, Takashi Iwai wrote:

> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index f851db7..314af26 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -356,6 +356,23 @@ static const intel_limit_t intel_limits_ironlake_display_port = {
>   	.find_pll = intel_find_pll_ironlake_dp,
>   };
>
> +static bool is_dual_link_lvds(struct drm_i915_private *dev_priv,
> +			      unsigned int reg)
> +{
> +	/* BIOS should set the proper LVDS register value at boot, but
> +	 * in reality, it doesn't set the value when the lid is closed;
> +	 * thus when a machine is booted with the lid closed, the LVDS
> +	 * reg value can't be trusted.  So we need to check "the value
> +	 * to be set" in VBT at first.
> +	 */
> +	if ((dev_priv->bios_lvds_val & LVDS_CLKB_POWER_MASK) ==
> +	    LVDS_CLKB_POWER_UP)
> +		return true;

Would slightly prefer if this was more like:

     if (dev_priv->bios_lvds_val)
             return !!(dev_priv->bios_lvds_val & LVDS_CLKB_POWER_MASK);

Since that way it eliminates some useless register reads in the normal 
case even for single-link.  Not going to insist on it though.

Looks really good otherwise, thanks!

Reviewed-by: Adam Jackson <ajax@redhat.com>

- ajax