Re: -EPROBE_DEFER and failed DSI panel probe

[Eric Anholt <eric@anholt.net>]

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Andrzej Hajda <a.hajda@samsung.com> writes:

> On 15.11.2017 21:26, Eric Anholt wrote:
>> I'm happy to have the DSI panel finally working on VC4 (just waiting on
>> https://lists.freedesktop.org/archives/dri-devel/2017-October/156407.html),
>> but now I've got another problem to solve.  It would be great if I could
>> include the DSI panel in our upstream DT, so that it automatically
>> worked when you plugged one in.  However, right now we return
>> -EPROBE_DEFER during bind unless the panel has actually shown up.  This
>> means that if you don't have the panel actually connected, you get this
>> sequence at startup:
>>
>> [   10.719929] [drm] Initialized
>> [   10.829510] vc4_hdmi 3f902000.hdmi: vc4-hdmi-hifi <-> 3f902000.hdmi mapping ok
>> [   10.844043] vc4-drm soc:gpu: bound 3f902000.hdmi (ops vc4_hdmi_ops [vc4])
>> [   10.848626] vc4-drm soc:gpu: bound 3f806000.vec (ops vc4_vec_ops [vc4])
>> [   10.850214] vc4-drm soc:gpu: failed to bind 3f700000.dsi (ops vc4_dsi_ops [vc4]): -517
>> [   10.856559] vc4-drm soc:gpu: master bind failed: -517
>>
>> [...]
>>
>> [   10.967718] rpi_touchscreen 3-0045: Atmel I2C read failed: -6
>>
>> Once the panel driver fails to probe, we never get asked to re-bind vc4,
>> and drm_of_find_panel_or_bridge looks like it would just give us
>> -EPROBE_DEFER again since the panel still wasn't registered.
>>
>> Does anyone have any suggestions for handling this?
>
> I guess you should call component_add only when all required resources
> are present(including panel), I suppose moving it to vc4_dsi_host_attach
> should help.

How can I decide when the panel driver has tried to probe and failed,
versus not tried to probe yet?  find_panel_or_bridge gives me
-EPROBE_DEFER either way.

> On the other side I am curious why EPROBE_DEFER from bind does not fail
> probing of some component (the last one probed), with proper error
> propagation it should cause defer_probing of one of the components or
> master, and probe/bind should be retried after panel's probe.

The panel probe failed, though, so there's no trigger to re-probe other
drivers.

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