Re: [PATCH] radeonfb: DDC i2c fix

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

On Fri, 2005-03-11 at 21:13 +0100, Kronos wrote:
> Il Fri, Mar 11, 2005 at 04:46:10PM +1100, Benjamin Herrenschmidt ha scritto: 
> > The radeonfb code for DDC probing (like it's X.org counterpart) uses to
> > leave the DDC clock & data lines asserted after the probing is complete.
> > This causes problems with some Apple monitors like the new Cinema HD
> > 23", who will turn themselves off when that happens. This fixes it.
> 
> Fix is correct, but comment is not ;) After the loop SCL and SDA are
> left low. Pulling them high puts the I2C bus in the stop condition.

Well, they are pull-up lines. I'm not pulling them high per-se, I'm
"releasing" them to their natural state, which is high ;) The ATI code
does some weird shit around the i2c transfer proper, and I don't know
exactly why. I don't have any spec about DDC2 though, my understand is
that it's more than just i2c EEPROM though. It used to leave the 2 lines
"assserted" at the end of the transfer (after the last stop condition)
and that sounded wrong and causes the misbehaviour  on the Apple
display ...

Ben.




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