[Intel-gfx] Thinkpad T420 and single/dual channel lvds

[Andreas Heider]

Am 18.03.2012 um 18:50 schrieb Daniel Vetter:
> On Fri, Mar 16, 2012 at 09:29:24PM +0100, Takashi Iwai wrote:
>> At Fri, 16 Mar 2012 15:55:52 -0400,
>> Adam Jackson wrote:
>>> 
>>> 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.
>> 
>> Sounds reasonable, yes.
>> 
>> Also, it'd be good to have a module option to override the lvds
>> channel setup, e.g. lvds_channel=0 for probing BIOS like this,
>> lvds_channel=1 and 2 are to set the single and dual-channel mode
>> forcibly, respectively.  If you guys think it's worth, I'll write an
>> additional patch after fixing this as suggested.
> 
> I think we can wait with adding debug options until this blows up. And if
> there are indeed broken bios out there, we need a full quirk table anyway.
> 
> I'll wait for the new patch with Adam's suggestion for merging into -next.
> -Daniel

Hi,

I tried this patch on a Macbook Pro 6,2 and indeed still need to manually set lvds_channel=2. 
It'd be great if this patch with the override parameter or some other way to fix it would end up in mainline.

Cheers,
Andreas

> -- 
> Daniel Vetter
> Mail: daniel at ffwll.ch
> Mobile: +41 (0)79 365 57 48
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