[PATCH v2 12/26] drm/exynos: Split manager/display/subdrv

[Olof Johansson]

On Wed, Oct 23, 2013 at 9:09 AM, Sean Paul <seanpaul at chromium.org> wrote:
> On Wed, Oct 23, 2013 at 11:53 AM, Dave Airlie <airlied at gmail.com> wrote:
>>>>>>>
>>>>>>
>>>>>> I think we need to start considering a framework where subdrivers just
>>>>>> add drm objects themselves, then the toplevel node is responsible for
>>>>>> knowing that everything for the current configuration is loaded.
>>>>>>
>>>>>
>>>>> It would be nice to specify the various pieces in dt, then have some
>>>>> type of drm notifier to the toplevel node when everything has been
>>>>> probed. Doing it in the dt would allow standalone drm_bridge/drm_panel
>>>>> drivers to be transparent as far as the device's drm driver is
>>>>> concerned.
>>>>>
>>>>> Sean
>>>>>
>>>>>
>>>>>> I realise we may need to make changes to the core drm to allow this
>>>>>> but we should probably start to create a strategy for fixing the API
>>>>>> issues that this throws up.
>>>>>>
>>>>>> Note I'm not yet advocating for dynamic addition of nodes once the
>>>>>> device is in use, or removing them.
>>>>>>
>>>>
>>>> I do wonder if we had some sort of tag in the device tree for any nodes
>>>> involved in the display, and the core drm layer would read that list,
>>>> and when every driver registers tick things off, and when the last one
>>>> joins we get a callback and init the drm layer, we'd of course have the
>>>> basic drm layer setup prior to that so we can add the objects as the
>>>> drivers load. It might make development a bit trickier as you'd need
>>>> to make sure someone claimed ownership of all the bits for init to proceed.
>>>>
>>>
>>> Yeah, that's basically what the strawman looked like in my head.
>>>
>>> Instead of a property in each node, I was thinking of having a
>>> separate gfx pipe nodes that would have dt pointers to the various
>>> pieces involved in that pipe. This would allow us to associate
>>> standalone entities like bridges and panels with encoders in dt w/o
>>> doing it in the drm code. I *think* this should be Ok with the dt guys
>>> since it is still describing the hardware, but I think we'd have to
>>> make sure it wasn't drm-specific.
>>>
>>
>> I suppose the question is how much dynamic pipeline construction there is,
>>
>> even on things like radeon and i915 we have dynamic clock generator to
>> crtc to encoder setups, so I worry about static lists per-pipe, so I still
>> think just stating all these devices are needed for display and a list of valid
>> interconnections between them, then we can have the generic code model
>> drm crtc/encoders/connectors on that list, and construct the possible_crtcs
>> /possible_clones etc at that stage.
>>
>
> I'm, without excuse, hopeless at devicetree, so there are probably
> some violations, but something like:

This is definitely worth discussing. I know device-tree but not DRM so
let's see if we can figure this out together. :)

>
> display-pipelines {
>   required-elements = <&bridge-a &panel-a &encoder-x &encoder-y
> &crtc-x &crtc-y>;

What's this supposed to mean? Are all these elements required to get
DRM up on this particular platform? Or are they just enumerating all
the possible devices that might be involved?

>   pipe1 {
>     bridge = <&bridge-a>;
>     encoder = <&encoder-x>;
>     crtc = <&crtc-y>;
>   };
>   pipe2 {
>     encoder = <&encoder-x>;
>     crtc = <&crtc-x>;
>   };
>   pipe3 {
>     panel = <&panel-a>;
>     encoder = <&encoder-y>;
>     crtc = <&crtc-y>;
>   };

Maybe it's the use of pipe as a keyword that's confusing me here, and
my lack of DRM knowledge, but wouldn't it make more sense to focus on
output connectors here? I.e. describe the outputs such as eDP, LVDS,
HDMI. The bridge, such as edp-to-lvds, should possibly be specified
under the edp node instead of in the drm node here.

Also, while the hardware can allow a very flexible connection of
pipes, I'm guessing that in reality nearly all usage of these will
follow a few common patterns, so maybe it's not required to be able to
describe the full graph in device tree?

> I'm tempted to add connector to the pipe nodes as well, so it's
> obvious which connector should be used in cases where multiple
> entities in the pipe implement drm_connector. However, I'm not sure if
> that would be NACKed by dt people.

As mentioned above, it might make sense to turn it around and describe
it around the connectors instead of the pipes.

> I'm also not sure if there are too many combinations for i915 and
> radeon to make this unreasonable. I suppose those devices could just
> use required-elements and leave the pipe nodes out.


-Olof