[Intel-gfx] [PATCH 1/2] drm/i915/crt: Remove 0xa0 probe for CRT

[Chris Wilson]

On Mon, 04 Apr 2011 08:08:40 -0700, Keith Packard <keithp at keithp.com> wrote:
> On Mon,  4 Apr 2011 07:26:44 +0100, Chris Wilson <chris at chris-wilson.co.uk> wrote:
> 
> > Following the fix to reset the GMBUS controller after a NAK, we finally
> > utilize the 0xa0 probe for a CRT connection. And discover that it is
> > useless as it simply detects the presence of the controller and not the
> > actual monitor. Given that we already probe 0x50 prior to performing the
> > EDID retrieval, we can simply remove the redundant probe to 0xa0.
> 
> I don't understand -- are you saying that there is additional hardware
> somewhere in the machine responding to I2C transactions on the monitor's
> DDC bus?

Yes. I'm saying that that the controller accepts a write to port 0xa0.
 
> And if so, how was this extra transaction breaking things? The GMBUS
> reset patch should only have an effect when there are failed
> transactions, not successful ones, and then it should only cause future
> transactions to fail, not succeed. Besides, the 0xA0 transaction looks
> like the first one on the bus.

We do several i2c xfers before CRT.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre