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TPS65982: Display port entry

WST
Expert 1015 points
Part Number: TPS65982

I have the TPS65982 'Display Port Config (0x51)' register set to 'DP Port Capability' to 'UFP_D and DFP_D capable Device'.

The 'Enable Display Port SID' and 'Enable Display Port Mode' are set, as are 'C' and 'D' modes for the UFPD receptacle assignment.

When I connect my board to a Huawei phone it won't go into DisplayPort mode, even though the Display port status says it is all ok.
I have to change the Port Capability to 'DP UFP_D only' to get it to work.
WHY??  Other display port sources have no problem with this, such as PCs I connect to. It seems like if I negotiate that my board is an UF device, then the DF device should pick the correct display port mode and turn on.

Is the Huawei phone misbehaving?

  • 0
    TI__Mastermind 36756 points

    Hi WST,

    From your description, it sounds like the Huawei phone is misbehaving. If you have a PD analyzer available, you can check the PD messaging to ensure the phone is correctly entering DisplayPort mode and sending all the correct DP configuration messages.

    However, there is no issue with your configuration, I tested the same settings here using a TPS65982EVM and Samsung S8 phone and was able to enter DisplayPort mode correctly.

    If this answers your question, PLEASE select This resolved my issue

    Thank you,
    Eric

  • 0 in reply to Eric Beljaars
    Expert 1015 points
    That is interesting. Our support people said that the Samsumg S8 phone has the same problem, but the S9 does not. I don't either of those phones, the Huawei phone is a Mate 10 phone. They said it also doesn't work on the Mate 20. So your setting for the register was 'UFP_D and DFP_D capable Device' and it went into display port mode without an issue on the Samsung S8? Could there be some other setting in one of the other registers that is affecting this?
    I haven't looked at the PD traffic yet.
    Also, if I use a DP dongle, a cable with the usb-c connector to a display port connector with some hardware on the cable, and look at the traffic with a display port monitor it looks like the Huawei phone goes into display port mode.
  • 0 in reply to WST
    TI__Mastermind 36756 points
    Hi WST,

    The use cases for "DP dongle, a cable with the usb-c connector to a display port connector with some hardware on the cable" are a bit different than the TPS65982 configured as both UFP_D and DFP_D.
    Those devices are only UFP_D. It could be that the Huawei phone is confused when the DP Capabilities advertised to it have both UFP_D and DFP_D capabilities.

    Thanks,
    Eric
  • 0 in reply to Eric Beljaars
    Expert 1015 points
    Eric,
    1st, thanks so much for the quick replies!!!
    To clarify what you said...
    1) You were able to get the Samsung S8 phone to go into display port ALT mode even with the 'UFP_D and DFP_D capable device setting'?
    2) Are you saying I shouldn't have to use the 'UFP_D Capable Device' only setting? I don't think that is a problem to change that, but I'm wondering why I would need to if the contract is made with the phone being the DFP. Shouldn't it figure out that it can put out the display port signals. I think it is a Huawei/Hisilicon interface IC, but if Samsung is also having issues, maybe the setting has to be fixed at UFP_D only.
    3) If I have the 'Initiate' and 'Process Swap to DFP' unchecked (in register 0x29), then it would seem that the phone should work without problems.
    4) I'm guessing that it is normal to only have one of these options for a certain product, either UFP_D -OR- DFP_D and not both. Maybe that is why the phone doesn't expect this option. Can you tell me when the 'BOTH' would be used in a product? Maybe in a laptop?
  • 0 in reply to WST
    TI__Mastermind 36756 points

    Hi WST,

    1. Yes, with the Samsung S8, I can enter DP mode with UFP_D and DFP_D setting

    2. I was suggesting setting to UFP_D only, to workaround the Huawei phone issue. The Huawei phone could be confused when it sees both DFP_D and UFP_D settings from the connected device. I agree that setting to UFP_D would probably be the more robust setting. If your device will only ever take video data from the connected device (like a monitor), then there is no reason to allow DFP_D mode.

    3. The Initiate and Process Swap to DFP bits in register 0x29 are regarding the USB PD Data role. This does not relate to the DisplayPort Alt Mode data role. With USB PD, your data role can be either DFP or UFP, simultaneously, DisplayPort data role can be UFP_D or DFP_D. The "_D" indicates the DisplayPort data role.

    4. The "both" setting would most commonly be used in a tablet. The use case would be you either want to display the tablet's screen on another monitor or if you connect a laptop or phone, you can use the tablet's screen as a secondary display.

    Thanks,
    Eric

  • 0 in reply to Eric Beljaars
    Expert 1015 points
    Eric,
    Thanks again for the response. As to #1 above, I wanted to check the same using an EVM board with the Huawei phone. However, I saw no switch settings for DP ALT mode support that allowed the BOTH setting. I have attached an Aardvark debugger and can modify the register that way, but I also had to attach an external supply to the EVM board because if not, when I pulled out the usb-c cable and re-attached the modified registers went back to the original values.
    Indeed, when I did it properly, I found that the Huawei phone doesn't like the 'BOTH' setting, even using the EVM board. Our support people said the S8 behaves the same way, but maybe they weren't connecting in their system correctly.
    Can you tell me how you tested the S8 phone, and what switch setting you started with? Did you use the external debugger to read the Data Status?
    Thanks for the explanation on #3 above, I suspected that the USB PD and the DPort DP were different, maybe that is also confusing the Huawei connection. It looks like the best solution is just to present the UFP_D displayport role unless we have a need to supply video.

    Thanks very much,
    Warren
  • 0 in reply to WST
    TI__Mastermind 36756 points
    Hi WST,

    I didn't use one of the dip-switch settings. I created my own image to support this setting. However, it should be the same with regards to DP mode as what you did. I agree that the best setting would be to only present UFP_D unless your device needs to source video out of it.

    Thanks,
    Eric