[RFC PATCH v2 00/21] Add DSI display support for Exynos based boards

[Inki Dae]

2014-03-07 19:00 GMT+09:00 Andrzej Hajda <a.hajda at samsung.com>:
> On 03/05/2014 03:56 AM, Inki Dae wrote:
>> Hi Andrzej,
>>
>> Thanks for your contributions.
>>
>> 2014-02-12 20:31 GMT+09:00 Andrzej Hajda <a.hajda at samsung.com>:
>>> Hi,
>>>
>>> This patchset adds drivers and bindings to the following devices:
>>> - Exynos DSI master,
>>> - S6E8AA0 DSI panel,
>>> - TC358764 DSI/LVDS bridge,
>>> - HV070WSA-100 LVDS panel.
>>>
>>> It adds also display support in DTS files for the following boards:
>>> - Exynos4210/Trats,
>>> - Exynos4412/Trats2,
>>> - Exynos5250/Arndale.
>>>
>>> Things worth mentioning:
>>>
>>> 1. I have implemented DSI/LVDS bridge using drm_panel framework, ie.
>>> the driver exposes drm_panel interface on DSI side, and interact with
>>> panels on LVDS side using drm_panel framework. This approach seems to
>>> me simpler and more natural than using drm_bridge.
>> Can you give me more details about why you think better to use panel
>> framework than using drm_bridge?  "Simpler" and "more natural" are
>> ambiguous to me.
> In this particular case DSI master expects on the other end
> any device having DSI slave interface, it could be panel or bridge.
> So it seems natural that both types of slave devices should expose
> the same interface also  on programming level.
> Another problem with drm_bridge is that it is not scalable -
> if some manufacturer will decide to add another block between the bridge
> and the panel there is no drm component which can be used for it.
> Using drm_panel the way I have used in toshiba bridge makes scalability
> possible,
> it will be only a matter of adding a driver for new block and making
> proper links in device tree, I see no easy way of doing it with
> drm_bridge approach.

Now drm_bridge may not cover all hardware. However drm_bridge has
already been merged to mainline so I think we need to use drm_bridge
somehow instead of using other one, and also we could extend
drm_bridge if needed. It would be definitely impossible for a new
framework to cover all hardware because there may be other hardware
not appeared yet. That is what we are doing for mainline until now.

>
>
>>
>> Using same drm_panel framework for LDVS bridge and real panel drivers
>> isn't reasonable to me as now because drm_panel framework would be for
>> real panel device even if the use of drm_panel framework looks like
>> suitable to LVDS bridge driver. I thought Sean's way, ptn3460 driver
>> using drm_bride stuff, is good enough, and that would be why
>> drm_bridge exists and why drm_encoder has drm_bridge.
>>
>> And I'm finding more generic way, how to handle LVDS bridge using
>> super node so that  LVDS bridge driver isn't embedded to connector
>> drivers such as eDP and MIPI-DSI, and dt binding of LVDS bridge can be
>> done at top level of Exynos drm. Once the binding is done, encoder of
>> display bus driver will have drm_bridge object of LVDS bridge driver
>> so that display bus driver can handle LVDS bridge driver.
> Could you explain what you mean by "dt binding of LVDS bridge can be
> done at top level of Exynos drm" ? How it will look like if there
> will be more bridges, one for DSI, one for HDMI, etc... What if there
> will be two
> bridges in one chain. How it will cope with video pipeline bindings?

it was just my idea so I have no implementation about it yet.

My idea is that crtc and encoder are binded at top level of Exynos drm
as is. And for bridge support, the only difference is, in case that
encoder driver has bridge, the dt binding of the encoder driver is
done once last one between encoder and bridge driver is binded. It
would mean that bridge driver can use driver model and it doesn't need
to concern about probe order issue.

For this, encoder driver with bridge, MIPI-DSI or eDP, would need to
use component interfaces specific to Exynos drm. As a result, once the
dt bindings of crtc and encoder are completed at top level, encoder
driver has its own drm_bridge for bridge, and dt binding you proposed
could be used without any change, and drm_panel could also be used
only for real lcd panel driver.

And below is a block diagram I think,

                                  DRM KMS
                   /                      |                 \
              /                           |                      \
         crtc                      encoder              connector
           |                           /     \                          |
           |                       /             \                      |
           |                      |           drm_bridge   drm_panel
           |                      |                   |                 |
           |                      |                   |                 |
        FIMD         MIPI-DSI    LVDS bridge    Panel


Thanks,
Inki Dae

>>
>> Will review your patch series soon.
> Thanks in advance.
>
> Regards
> Andrzej
>
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