[Intel-gfx] [PATCH 3/3] drm/i915: add i915.dp_link_train_policy option

[Daniel Vetter]

On Fri, Apr 25, 2014 at 10:06 AM, Daniel Vetter <daniel at ffwll.ch> wrote:
> On Thu, Apr 24, 2014 at 06:22:59PM -0300, Paulo Zanoni wrote:
>> From: Paulo Zanoni <paulo.r.zanoni at intel.com>
>>
>> We still have way too many bugs with DP link training. We keep
>> switching between "narrow and fast" and "wide and slow", we recently
>> added 5GHz support, and whenever there's a bug report, we have to ask
>> people to apply patches and test them.
>>
>> Wouldn't it be so much better if we could just ask them to boot with
>> some specific Kernel boot option instead of applying a patch? This
>> will move the situation from "i915.ko is completely broken!" to
>> "i915.ko's default values are broken, but there's an option I can set
>> to fix it, so I won't need to learn how to compile a Kernel!".
>>
>> Some useful values:
>>  - i915.dp_link_train_policy=1 for "wide and slow"
>>  - i915.dp_link_train_policy=0x120 for DP_LINK_BW_2_7 and 2 lanes,
>>    which should be able to fit 1920x1080 at 60Hz and 24bpp
>>  - i915.dp_link_train_policy=0x210 to force DP 5GHz testing on
>>    not-so-huge modes
>>
>> The default behavior is still the same.
>>
>> Signed-off-by: Paulo Zanoni <paulo.r.zanoni at intel.com>
>
> Yeah, I like this. I'll sign up Todd to review this all.

Now with Todd actually cc'ed.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch