[PATCH v3 06/14] Documentation: drm/bridge: add document for analogix_dp

Yakir Yang ykk at rock-chips.com
Tue Aug 25 07:23:24 PDT 2015

Hi Thierry,

在 2015/8/25 22:16, Thierry Reding 写道:
> On Tue, Aug 25, 2015 at 09:48:01PM +0800, Yakir Yang wrote:
>> Hi Thierry & Rob,
>> 在 2015/8/25 21:27, Rob Herring 写道:
>>> On Tue, Aug 25, 2015 at 4:15 AM, Thierry Reding <treding at nvidia.com> wrote:
>>>> On Sun, Aug 23, 2015 at 06:23:14PM -0500, Rob Herring wrote:
>>>>> On Wed, Aug 19, 2015 at 9:50 AM, Yakir Yang <ykk at rock-chips.com> wrote:
>>>> [...]
>>>>>> +       -analogix,link-rate:
>>>>>> +               max link rate supported by the eDP controller.
>>>>>> +                       LINK_RATE_1_62GBPS = 0x6, LINK_RATE_2_70GBPS = 0x0A,
>>>>>> +                       LINK_RATE_5_40GBPS = 0x14
>>>>> Same here. I'd rather see something like "link-rate-mbps" and use the
>>>>> actual rate.
>>>> There is no need whatsoever to hard-code this in DT. (e)DP provides the
>>>> means to detect what rate the link supports and the specification
>>>> provides guidance on how to select an appropriate one.
>>> Good, even better.
>> I do think we still need keep this DT prop yet.
>> I think drm_dp_help.c could get the "panel" max link-rate and lane-count,
>> but it's not enough, we still need knew the "eDP controller" max link-rate
>> and lane-count.
>> Let me show the exact example that happened in my side. When I connect
>> my board to my 2K DP-1.2 TV. Analogix dp driver would get the max link-rate
>> from dpcd, and the max link-rate is 5.4Gbps. So if I just set eDP controller
>> link-rate
>> to 5.4Gbps, the DP TV just broken, do not light up normally.
>> This reason why TV broken is the max link-rate which support by RK3288 eDP
>> controller is 2.7Gbps. Here are the exact words that RK3288 eDP TRM said:
>> *Compliant with DisplayPortTM Specification, Version 1.2.
>> Compliant with eDPTM Specification, Version 1.3.
>> HDCP v1.3 amendment for DisplayPortTM Revision 1.0.
>> Main link containing 4 physical lanes of 2.7/1.62 Gbps/lane
>> *
>> **
>> Beside I haven't found there are some registers would indicate the eDP
>> controller
>> max link-rate and lane-count, so this is why I still instance that we need
>> this DT
>> prop to indicata "Max rate controller support".
>> So, I wish you could agree with me on this point.
> Your driver should know what link rates it supports and restrict itself
> to use those. This is implied by the compatible string and doesn't need
> to be duplicated into device tree.

Oh, yeah, good idea   :-D
Thanks for your point out.

- Yakir

> Thierry

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