[Intel-gfx] DisplayPort support

[Paul McGarry]

On Wed, Apr 27, 2011 at 7:00 PM, Chris Wilson <chris at chris-wilson.co.uk> wrote:

> The unusual sequence appears to be:
>
> [   30.081906] [drm:intel_dp_i2c_init], i2c_init DPDDC-B
> [   30.082413] [drm:intel_dp_aux_ch], dp_aux_ch timeout status 0x5143003e
> [   30.082415] [drm:intel_dp_i2c_aux_ch], aux_ch failed -110
> [   30.082921] [drm:intel_dp_aux_ch], dp_aux_ch timeout status 0x5143003e
> [   30.082923] [drm:intel_dp_i2c_aux_ch], aux_ch failed -110
> [   30.082986] [drm:intel_dp_i2c_init], i2c_init DPDDC-C
> [   30.083193] [drm:intel_dp_i2c_aux_ch], aux_i2c nack
> [   30.083401] [drm:intel_dp_i2c_aux_ch], aux_i2c nack
> [   30.083427] [drm:intel_dp_i2c_init], i2c_init DPDDC-D
> [   30.083934] [drm:intel_dp_aux_ch], dp_aux_ch timeout status 0x5143003e
> [   30.083935] [drm:intel_dp_i2c_aux_ch], aux_ch failed -110
> [   30.084442] [drm:intel_dp_aux_ch], dp_aux_ch timeout status 0x5143003e
> [   30.084443] [drm:intel_dp_i2c_aux_ch], aux_ch failed -110
>
> I wonder what side-effects that explicit NAK from the monitor does during
> initialisation of the DP i2c channel.
>
> During detection we also see a discrepancy for DPDDC-D:
>
> [   30.172250] [drm:drm_helper_probe_single_connector_modes],
> [CONNECTOR:19:DP-2]
> [   30.172757] [drm:intel_dp_aux_ch], dp_aux_ch timeout status 0x5013003e
> [   30.172758] [drm:ironlake_dp_detect], DPCD: 0000
>
> So instead of sending the expected 20 bytes to query the connection, we
> just sent the 1 byte header. It seems our problems start with that nack.
>
> Lets start with a WARN for the AUX_I2C_REPLY_NACK so that I can see the
> callpath for that initial probe and so work out the command being sent
> that the monitor doesn't like.
> -Chris

I am keen to help get to the bottom of this but I'll need some
direction, it is a long time since I have compiled a kernel, let alone
muddled with one.

I have got the source packages for my OS kernel and will work out how
to build it etc.

Looking at the source
 intel_dp.c
seems to be where I might add stuff to get more info based on the
above but it might be more productive to tell me what to add than
randomly poking it by myself.

Paul