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

Ajay kumar ajaynumb at gmail.com
Thu May 8 03:52:14 PDT 2014


On Thu, May 8, 2014 at 1:14 PM, Inki Dae <inki.dae at 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.
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
4) Inki's suggestion is to combine drm_bridge, drm_panel and
drm_enhance into a single

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.


>> 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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