Re: VESA, EDID & flat panels

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

> Here's a snippet from the HDMI specs. Not sure how helpful this is
> 
> "8.4.3 Segment pointer
>  Enhanced DDC allows access of up to 32 Kbytes of data. This is accomplished
>  using a combination of the 0xA0/0xA1 address pair and a segment pointer. For
>  each value of the segment pointer, 256 bytes of data are available at the
>  0xA0/0xA1 address pair. An unspecified segment pointer references the same
>  data as when the segment pointer is zero. Each successive value of the
>  segment pointer allows access to the next two blocks of E-EDID (128 bytes
>  each). The value of the segment pointer register cannot be read since it is
>  reset at the completion of each command."

Yes, I have that. The problem is that the "primary" (old style) EDID
block is supposed to contain in byte 0x7e, a value that indicates if
there are extended stuffs available... Actually, it should contain:

 0 - no extended infos
 1 - one more 128 bytes extension (basically to be read from the same
0xa0 address, as each i2c address can actually return up to 256 bytes of
data)
 3 - more extension blocks. The EEDID spec then talks about a "map" of
the segments but I'm not sure where that is to be found.

The problem is that so far, all EDID blocks I've seen have this bit
clear. Also, on the couple of machines i've tested, the additional 128
bytes at address 0xa0 aren't there neither.

So I wonder how widespread really is that EEDID stuff... I'm afraid the
reason a lot of monitors come with a windows install CD is that they do
_not_ provide those infos via EDID, but windows has a database with
per-monitor infos (as Apple actually has in OS X) and we should probably
do something similar. (but not in the kernel)

Ben.




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