drivers/gpu/drm/bridge/lvds-encoder.c broken in mainline

[Archit Taneja]

On 11/14/2017 02:33 AM, Eric Anholt wrote:
> Lothar Waßmann <LW at KARO-electronics.de> writes:
> 
>> Hi,
>>
>> On Wed, 08 Nov 2017 10:18:03 -0800 Eric Anholt wrote:
>>> Lothar Waßmann <LW at KARO-electronics.de> writes:
>>>
>>>> Hi,
>>>>
>>>> drivers/gpu/drm/bridge/lvds-encoder.c driver is currently
>>>> dysfunctional due to:
>>>> |commit 13dfc0540a575b47b2d640b093ac16e9e09474f6
>>>> |Author: Eric Anholt <eric at anholt.net>
>>>> |Date:   Fri Jun 2 13:25:14 2017 -0700
>>>> |
>>>> |    drm/bridge: Refactor out the panel wrapper from the lvds-encoder bridge.
>>>>
>>>> Also, there is no in-kernel user of this driver, so that it obviously
>>>> doesn't get tested in any way. There is only one dts file (r8a7779-marzen.dts)
>>>> that instantiates this driver, but it has an incomplete OF graph. The missing
>>>> link for the OF graph is provided by either r8a77xx-aa104xd12-panel.dtsi or
>>>> r8a77xx-aa121td01-panel.dtsi, but those files are referenced nowhere in
>>>> the kernel source.
>>>>
>>>> Should the driver be removed or moved to staging, until it is properly
>>>> fixed?
>>>
>>> I can't see any behavior change about the DT handling in that commit,
>>> and I didn't intend for there to be any.  Could you help me understand
>>> what went wrong?
>>>
>> With the offending commit applied, the lvds-encoder driver is being
>> attached to the device associated with the lcd-panel driver's of_node
>> (panel-simple in my case) rather than the lvds-encoder's of_node.
> 
> Anyone have any thoughts on best handling this?  Slip another bridge in
> attached to this of_node that chains to panel-bridge's bridge, or just
> have a panel-bridge entrypoint for what node to register the bridge on?

I think slipping in another bridge seems to make more sense. When we converted
to panel-bridge, we didn't create a bridge entity for the lvds-encoder itself,
we just created the panel-bridge's bridge, which anyway is more a glue-layer
for drm_panel than a real bridge entity.

Thanks,
Archit

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