[PATCHv3 22/23] drm/bridge: tc358767: add IRQ and HPD support

[Andrzej Hajda]

On 27.05.2019 17:11, Tomi Valkeinen wrote:
> On 21/05/2019 17:18, Andrzej Hajda wrote:
>
>>> DisplayPort spec talks about doing the display-props reading and EDID reading when
>>> handling HPD.
>>>
>>> I think it would be best to change the code so that we read display props and EDID in HPD,
>>> but so that we also can read them later (when needed, probably bridge enable and
>>> get_modes) if we haven't done the reads already. I've had this in mind since I started the
>>> series, but as it didn't feel like a simple change, I left it for later.
>>
>> My approach and experience suggest that detect, should be rather
>> lightweight and should not modify state, I am not even sure if it is
>> called at all on forced connector.
> I just realized that this is not exactly perfect...
>
> Link training can adjust the link speed and/or number of lanes, although 
> the driver doesn't support this at the moment. The speed and number of 
> lanes affect the video modes that are possible, so they affect get_modes.
>
> So... I think the driver should set up the link fully before get_modes 
> get called, instead of leaving the link setup to the point where we 
> enable the bridge. Maybe... This is not exactly clear to me =).


Moreover link state can change during work, so full implementation
should handle HPD pulses (below 1ms if I remember correctly) re-train if
necessary and use drm_connector_set_link_status_property as well :)


Regards

Andrzej


>
> In any case, I think that's future work. I have changed the code to read 
> the display props in get_modes(), and I have another small fix too. I'll 
> send v4 this week, and hopefully we can get this merged.
>
>   Tomi
>