[PATCHv2 03/22] drm/bridge: tc358767: fix ansi 8b10b use

[Tomi Valkeinen]

Hi Laurent, Andrey,

On 03/05/2019 20:11, Laurent Pinchart wrote:
>> I agree that if the panel Andrey mentioned is still used, we need to
>> handle it somehow. But I think explicitly handling such a case is better
>> than guessing.
> 
> The risk may not be worth it, I agree. I would explain this in details
> in the commit message though, and add a comment to the code as well, to
> ease future debugging.

Andrey, do you still have the panel that doesn't work with 8b10b? Is it
used in real life (i.e. it was not just a temporary development phase
panel)? What's the model, and is there a public datasheet?

Everywhere I look, I always see 8b10b as mandatory for all DP versions
for the main link. If the panel in question requires 8b10b to be
disabled, I would imagine that mentioned in its datasheet, as it's kind
of a big thing. I would guess that the panel doesn't work with many eDP
sources.

>> And isn't this something that's not really TC358767 specific? If that
>> panel is used with other bridges, we need to deal with this case with
>> those bridges too? Or is TC358767 the only bridge that allows disabling
>> 8b10b?
> 
> I don't know about other bridges, but I think it would need to be
> handled globally, yes.

Ok. This does sound like a relatively big work, adding a new field to
simple panel, or maybe a new DT property to the panels, and making the
bridges work use that data (even if we'd add the support only to
tc358767 for now).

I don't want to break Andrey's panel, but I have to say I'm not very
enthusiastic about this work either =).

The DP 1.0 spec does say that PRBS7 test pattern is not 8b10b encoded. I
understand this meaning that 8b10b is not used for some particular
tests, which would explain why 8b10b can be turned off in tc358767 (and
maybe that also means it can be turned off in all/most other DP sources).

 Tomi

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