Re: [PATCH] tegra: ventana: display and backlight DT entries

[Alex Courbot <acourbot-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>]

On Wednesday 14 November 2012 00:46:52 Stephen Warren wrote:
> I do tend to think that we should use EDID where there is one.
> 
> 1) If there is an EDID in the panel HW, and the panel's I2C is hooked
> up to Tegra, we should read it out at runtime.

According to Ventana' platform design guide the LCD panel is hooked on I2C2. 
The panel's data sheet lists CLK_EDID and DATA_EDID pins, which I assume are 
for I2C, but there is no mention of an I2C address in both guides.

> 2) Otherwise, if the panel's documentation provides an EDID, we should
> use that, since it's the most canonical/common/standard representation
> of the panel's properties.

Panel's documentation indeed provides full EDID specification in appendix. Mark 
sent me an EDID blob which works but I don't know where it comes from - Mark, 
could you tell us?

> 3) Otherwise, use the videomode DT bindings.
> 
> Another benefit of (2) is that we can actually support the panel
> without waiting for the videomode DT bindings to be finalized and merged.

Is there another incentive for preferring (2) over (3)? EDID specs can easily 
be turned into videomode bindings, and it would also avoid introducing a new 
file into the kernel source.

> Although if Ventana requires the power sequences helpers, that already
> means we won't be able to support Ventana's panel in 3.8 unless the
> power sequences code gets merged for 3.8; is that likely?

Likely, I don't know, possible - maybe. Power seqs work and I could push to 
get them merged, but the following points need to be considered:
- DT bindings are likely to change from their current form. I want to take 
advantage of the gpio API changes that are undergoing, and also probably of 
your preprocessor patch for dtc (not sure if that is already usable in the 
kernel?). Considering the feature is young I don't think a DT change would be 
a big deal, but the general consensus seems to be that DT bindings are 
immutable - maybe my perception is wrong?
- If I am to take maintainership of the feature, I guess I will have to get 
the patches sufficiently Ack'ed by enough people, and also have someone else 
pull from my tree (Linus? Or maybe some other power maintainer?). I am not 
familiar with the exact procedure here - moreover, my GPG key only has one 
signature from a trusted kernel dev, I am not sure if this is enough.

Alex.