[PATCH v11 20/24] arm64: dts: rockchip: enable vop2 and hdmi tx on rock-3a

[Robin Murphy]

On 2022-06-25 16:31, Piotr Oniszczuk wrote:
> 
> 
>> Wiadomość napisana przez Peter Geis <pgwipeout at gmail.com> w dniu 25.06.2022, o godz. 16:00:
>>
>>
>> The first issue you have is the TV isn't responding until the absolute
>> end.
> 
> I suspect this is because lack on idle gaps between cec commands sent from board to tv.
> Maybe TV sw. can't deal with consecutive commands without any idle between them?
> 
> It is interesting that disconnecting TV - so CEC line is driven only by board - rock3a still don't have any idle gaps while rock3b (and radxa 4.19 bsp) has them (very similar between 5.18mailine and 4.19 bsp).
> 
> How this is possible that change I/O from m0->m1 impacts _timings_ on free hanging CEC line?

Check all the pinctrl settings beyond just the function mux - pulls, 
drive strength, output type, etc. - the defaults tend to be all over the 
place, and rarely what you want.

Robin.

>> This strikes me as a signal integrity issue. Do you have an
>> oscilloscope (not a logic analyzer, you need voltages and ramp times)
>> to compare the working vs non-working signals? Check both sides of the
>> level shifter.
> 
> Indeed - i will verify this with digital oscilloscope.
> Already ordered and must await week or 2 for delivery :-(
> 
> My analog oscilloscope shows correct levels and slopes "seems" to be the same like in working (no memory so i can compare only visually on fuzzy screen)
> 
> For me key is to understand why on rock3a there is no any idles between cec commands - even when nothing is connected to bard (so cec is only sending and nothing external impacts cec state machine)....
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