Re: VESA, EDID & flat panels

["Antonino A. Daplas" <adaplas@gmail.com>]

Benjamin Herrenschmidt wrote:
> On Mon, 2005-10-03 at 18:18 -0500, Richard Smith wrote:
>>> Somebody around here has access to the VESA specs ? I'm trying to figure
>>> out if the EDID block, at least on recent flat panels, tells us wether
>>> the panel digital input is 6:6:6 or 8:8:8 ... If it's 6:6:6, we should
>>> enable dithering in drivers like radeon and "nv", while if 8:8:8, we
>>> should not. If not enabling it on a 6 bits panel, we end up with crappy
>>> looking gradients, if enabling it on a 8 bits panel, we basically end up
>>> sending a 6 bits signal to a 8 bits panel, thus reducing the quality.
>> We have  a copy from a few years ago.  Its not too descriptive if
>> IIRC.  I'll try to look at it tomorrow.
> 
> I found a lot of stuff on VESA Public site in fact. Looks like we really
> need to write some infrastructure to get to the EDID extensions :) They
> contain all sort of useful infos, though unfortunately, all of the
> panels I've come accross so far didn't seem to implement them =P
> 

It think it's because the (basic) EDID is retrieved with (basic) DDC
(address 0x50).  If I'm not mistaken, E-EDID is retrieved with E-DDC
(address 0xa0). I don't exactly know the protocol (E-DDDC specs are not
freely available), but try probing your i2c busses with:

i2cdump 0,1,2,etc 0xa0 

and see if you get anything.

Tony


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