Re: [RFC V2 0/3] drm/bridge: panel and chaining

[Inki Dae <inki.dae@samsung.com>]

On 2014년 05월 08일 19:52, Ajay kumar wrote:
> +Dave
> +Thierry
> 
> On Thu, May 8, 2014 at 1:14 PM, Inki Dae <inki.dae@samsung.com> wrote:
>>
>> Just re-sending with text mode. Sorry for this.
>>
>>
>> On 2014년 05월 08일 15:41, Andrzej Hajda wrote:
>>> On 05/05/2014 09:52 PM, Ajay Kumar wrote:
>>>> This patchset is based on exynos-drm-next-todo branch of Inki Dae's tree at:
>>>> git://git.kernel.org/pub/scm/linux/kernel/git/daeinki/drm-exynos.git
>>>>
>>>> I have just put up Rob's and Sean's idea of chaining up the bridges
>>>> in code, and have implemented basic panel controls as a chained bridge.
>>>> This works well with ptn3460 bridge chip on exynos5250-snow board.
>>>>
>>>> Still need to make use of standard list calls and figure out proper way
>>>> of deleting the bridge chain. So, this is just a rough version.
>>>
>>> As I understand this patchset tries to solve two things:
>>> 1. Implement panel as drm_bridge, to ease support for hardware chains:
>>> Crtc -> Encoder -> Bridge -> Panel
>>> 2. Add support to drm_bridge chaining, to allow software chains:
>>> drm_crtc -> drm_encoder -> drm_bridge -> drm_bridge,panel
>>>
>>> It is done using Russian doll schema, ops from the bridge calls the same
>>> ops from the next bridge and the next bridge ops can do the same.
>>>
>>> This schema means that all the bridges including the last one are seen
>>> from the drm core point of view as a one big drm_bridge. Additionally in
>>> this particular case, the first bridge (ptn3460) implements connector
>>> so it is hard to guess what is the location of the 2nd bridge in video
>>> stream chain, sometimes it is after the connector, sometimes before.
>>> All this is quite confusing.
>>>
>>> But if you look at the bridge from upstream video interface point of
>>> view it is just a panel, edp panel in case of ptn3460, ie ptn3460 on its
>>> video input side acts as a panel. On the output side it expects a panel,
>>> lvds panel in this case.
>>>
>>> So why not implement ptn3460 bridge as drm_panel which internally uses
>>> another drm_panel. With this approach everything fits much better.
>>> You do not need those (pre|post)_(enable|disable) calls, you do not need
>>> to implement connector in the bridge and you have a driver following
>>> linux driver model. And no single bit changed in drm core.
>>>
>>> I have implemented this way DSI/LVDS bridge, it was sent as RFC [1][2].
>>> It was not accepted as Inki preferred drm_bridge but as I see the
>>
>> Yes, in above email threads, I disagreed to using drm_panel framework
>> for bridge device, especially, to implement connector/encoder to crtc
>> driver.
>>
>> However, I thought that it'd be more generic way that lvds drivers use
>> driver-model, and the use of drm_panel infrastructure would be suitable
>> to doing this.
>>
>> So my intention in turn, was that LVDS driver uses integrated drm_bridge
>> based on drm_panel infrastructure[1], and RFC patch[2] for it. This way
>> is same as your proposal in the point that LVDS and Panel drivers use
>> driver-model. The only different point is that LVDS driver has some ops
>> specific to LVDS device, not using existing ops of drm_panel commonly:
>> we may need to consider the characteristic of LVDS device.
>>
>> [1]:http://www.spinics.net/lists/dri-devel/msg55555.html
>> [2]:http://www.spinics.net/lists/dri-devel/msg55658.html
>>
>> Thanks,
>> Inki Dae
> I am just consolidating the discussion happening here.
> 1) This patchset started from a discussion wherein I tried to combine
> drm_panel with drm_bridge.
>     https://www.mail-archive.com/linux-samsung-soc@vger.kernel.org/msg28943.html
> 2) Sean and Rob suggested to implement a chain of bridges and then
> consider adding
>     basic panel controls as a bridge.
> 3) Andrej's idea is to drop the existing bridge infrastructure and
> implement ptn3460 using drm_panel,
>     the same way he has implemented
> http://permalink.gmane.org/gmane.linux.drivers.devicetree/61559.
> 4) Inki's suggestion is to combine drm_bridge, drm_panel and
> drm_enhance into a single
>     drm_hw_block.
> 

And more thing, we would need to consider image enhancer device placed
between crtc and connector/encoder devices. And it'd better to rename
drm_hw_block to drm_bridge, and existing drm_bridge relevant codes
should be removed.

Thanks,
Inki Dae

> I am currently trying to implement (2):chaining of bridges, and I
> think we have not yet
> reached to a consensus. So adding few other people from drm community
> to comment.
> 
> Regards,
> Ajay
> 
>>> problems with drm_bridges I have decide to attract attention to much
>>> more cleaner solution.
>>>
>>> [1]: http://permalink.gmane.org/gmane.linux.drivers.devicetree/61559
>>> [2]: http://permalink.gmane.org/gmane.linux.kernel.samsung-soc/27044
>>>
>>> Regards
>>> Andrzej
>>>
>>>
>>>>
>>>> Ajay Kumar (3):
>>>>   [RFC V2 1/3] drm: implement chaining of drm bridges
>>>>   [RFC V2 2/3] drm/bridge: add a dummy panel driver to support lvds bridges
>>>>   [RFC V2 3/3] drm/bridge: ptn3460: support bridge chaining
>>>>
>>>>  .../bindings/drm/bridge/bridge_panel.txt           |  45 ++++
>>>>  drivers/gpu/drm/bridge/Kconfig                     |   6 +
>>>>  drivers/gpu/drm/bridge/Makefile                    |   1 +
>>>>  drivers/gpu/drm/bridge/bridge_panel.c              | 240 +++++++++++++++++++++
>>>>  drivers/gpu/drm/bridge/ptn3460.c                   |  21 +-
>>>>  drivers/gpu/drm/drm_crtc.c                         |  13 +-
>>>>  include/drm/bridge/bridge_panel.h                  |  37 ++++
>>>>  include/drm/drm_crtc.h                             |   2 +
>>>>  8 files changed, 360 insertions(+), 5 deletions(-)
>>>>  create mode 100644 Documentation/devicetree/bindings/drm/bridge/bridge_panel.txt
>>>>  create mode 100644 drivers/gpu/drm/bridge/bridge_panel.c
>>>>  create mode 100644 include/drm/bridge/bridge_panel.h
>>>>
>>>
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>>
> 

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