[Intel-gfx] [PATCH] drm/i915/dp: DPTX writes Swing/Pre-emphs(DPCD 0x103-0x106) requested during PHY Layer testing.

[Imre Deak]

On Fri, Aug 21, 2020 at 11:48:37PM -0700, Khaled Almahallawy wrote:
> Source needs to write DPCD 103-106 after receiving a PHY request to change
> swing/pre-emphasis after reading DPCD 206-207. This is especially needed if
> there is a retimer between source and sink and the retimer implements AUX_CH
> interception scheme to manage DP PHY settings (e.g. adjusting Swing/Pre-emphasis
> equalization level) for DP output channel . If the source doesn't write to
> DPCD 103-106, the retimer may not output the requested swing/pre-emphasis and
> eventually we fail compliance.
> 
> Signed-off-by: Khaled Almahallawy <khaled.almahallawy at intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_dp.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> index 79c27f91f42c..5044201ca742 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -5503,6 +5503,9 @@ void intel_dp_process_phy_request(struct intel_dp *intel_dp)
>  
>  	intel_dp_autotest_phy_ddi_enable(intel_dp, data->num_lanes);
>  
> +	drm_dp_dpcd_write(&intel_dp->aux, DP_TRAINING_LANE0_SET,
> +				intel_dp->train_set, intel_dp->lane_count);

This should be rebased on a recent change using instead
crtc_state->lane_count. That's also not completely correct since it's
not guaranteed that the output is enabled (having up-to-date link params
in crtc_state) at the time of this test request. Also
compliance.test_data.phytest has its own link params that may be
different from the ones in crtc_state.

I'm also not sure how intel_dp_autotest_phy_ddi_disable()/enable()
affects the vswing/pre-emp setting of the source (DPTX) that got inited
when the output was last enabled. The vs/pe programming sequence should
be also part of the port enabling. Maybe the HW retains the config
across the the above port disable/enable calls and so this happens not
to be a problem.

There's been a discussion earlier that instead of open-coding here all
the port enabling/disabling and link training programming sequences the
driver's actual modesetting and link training code should be used
instead, making those aware of the modified PHY test request link
parameters. I suppose until that's done we could still merge this patch
with the above intel_dp/crtc_state fix after you can confirm that this
PHY test functionality actually works atm.

--Imre

> +
>  	drm_dp_set_phy_test_pattern(&intel_dp->aux, data,
>  				    link_status[DP_DPCD_REV]);
>  }
> -- 
> 2.17.1
>