Re: [PATCH] drm/i915/skl: Add module parameter to select edp vswing table

Jani Nikula
2015-05-06T06:59:32Z

On Wed, 06 May 2015, "Jindal, Sonika" <sonika.jindal@intel.com> wrote:
> On 5/5/2015 7:28 PM, Jani Nikula wrote:
>> On Tue, 05 May 2015, Damien Lespiau <damien.lespiau@intel.com> wrote:
>>> On Tue, May 05, 2015 at 02:39:48PM +0300, Jani Nikula wrote:
>>>> There's still the question whether we can default to using the vbt value
>>>> if that can be broken...
>>>
>>> This is a workaround for SDPs loaded with a "default" VBT which doesn't
>>> correspond to the full fleet of SPDs. For actual product, it's really
>>> expected to have a VBT with a correct low vswing bit set, otherwise the
>>> panel won't lit up (even on Windows!).
>>>
>>> It's probably a good idea to add a comment saying that's it's a
>>> workaround for early platform with generic-ish VBT. Something that we
>>> should remove in a bit.
>>
>> Thanks for the clarification, Damien. That settles the default then. I'd
>> still like the module parameter to be effective even if changed runtime.
>>
> This is used while preparing ddi buffers to program ddi_buf_trans during
> driver load. It will not really have any effect at runtime until power
> well is disabled/re-enabled.

Right, missed that part, sorry.

> PLease let me know if you still see the need of moving the check
> directly in prepare_ddi_buffers.

No, it would be confusing. And I guess we'll remove this parameter
afterwards anyway?

Please just change the module parameter permissions to read only, so
it's not possible to change it dynamically via sysfs.

BR,
Jani.

>
> Regards,
> Sonika
>> BR,
>> Jani.
>>
>>
>>
>>>
>>> --
>>> Damien
>>

--
Jani Nikula, Intel Open Source Technology Center