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

Yakir Yang <ykk@xxxxxxxxxxxxxx> · Tue, 25 Aug 2015 21:48:01 +0800



    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@xxxxxxxxxx> 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@xxxxxxxxxxxxxx> 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. 

    
    Thanks,

    - Yakir

    
      Rob


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