[RFC PATCH 2/7] drm/msm/dp: support attaching bridges to the DP encoder

[Kuogee Hsieh]

On 1/6/2022 9:26 PM, Dmitry Baryshkov wrote:
> On 07/01/2022 06:42, Stephen Boyd wrote:
>> Quoting Dmitry Baryshkov (2022-01-06 18:01:27)
>>> Currently DP driver will allocate panel bridge for eDP panels.
>>> Simplify this code to just check if there is any next bridge in the
>>> chain (be it a panel bridge or regular bridge). Rename panel_bridge
>>> field to next_bridge accordingly.
>>>
>>> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov at linaro.org>
>>> ---
>>>   drivers/gpu/drm/msm/dp/dp_display.c |  2 +-
>>>   drivers/gpu/drm/msm/dp/dp_display.h |  2 +-
>>>   drivers/gpu/drm/msm/dp/dp_drm.c     |  4 ++--
>>>   drivers/gpu/drm/msm/dp/dp_parser.c  | 26 ++++++++------------------
>>>   drivers/gpu/drm/msm/dp/dp_parser.h  |  2 +-
>>>   5 files changed, 13 insertions(+), 23 deletions(-)
>>
>> I like this one, it certainly makes it easier to understand.
>>
>>> diff --git a/drivers/gpu/drm/msm/dp/dp_parser.c 
>>> b/drivers/gpu/drm/msm/dp/dp_parser.c
>>> index a7acc23f742b..5de21f3d0812 100644
>>> --- a/drivers/gpu/drm/msm/dp/dp_parser.c
>>> +++ b/drivers/gpu/drm/msm/dp/dp_parser.c
>>> @@ -307,11 +299,9 @@ static int dp_parser_parse(struct dp_parser 
>>> *parser, int connector_type)
>>>          if (rc)
>>>                  return rc;
>>>
>>> -       if (connector_type == DRM_MODE_CONNECTOR_eDP) {
>>
>> It feels like this is on purpose, but I don't see any comment so I have
>> no idea. I think qcom folks are concerned about changing how not eDP
>> works. I'll have to test it out locally.
>
> Ah, another thing that should go into the commit message.
>
> Current situation:
> - DP: no external bridges supported.
> - eDP: only a drm_panel wrapped into the panel bridge
>
> After this patch:
> - both DP and eDP support any chain of bridges attached.
>
>
> While the change means nothing for the DP (IIUC, it will not have any 
> bridges), it simplifies the code path, lowering the amount of checks.
>
> And for eDP this means that we can attach any eDP-to-something bridges 
> (e.g. NXP PTN3460).
>
>
> Well... After re-checking the source code for 
> devm_drm_of_get_bridge/drm_of_find_panel_or_bridge I should probably 
> revert removal of the check. The function will return -ENODEV if 
> neither bridge nor panel are specified.
>
I am new to drm and  confusing with bridge here.

Isn't bridge used to bridging two different kind of interface together?

for example, dsi <--> bridge <--> dp.

why edp need bridge here?

Can you give me more info regrading what bridge try to do here.



>>
>>> -               rc = dp_parser_find_panel(parser);
>>> -               if (rc)
>>> -                       return rc;
>>> -       }
>>> +       rc = dp_parser_find_next_bridge(parser);
>>> +       if (rc)
>>> +               return rc;
>>>
>>>          /* Map the corresponding regulator information according to
>>>           * version. Currently, since we only have one supported 
>>> platform,
>
>