Re: [PATCH 12/14] drm/i915: Turn on panel power before doing aux transfers

[Imre Deak <imre.deak@intel.com>]

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On Mon, 2014-08-18 at 22:16 +0300, ville.syrjala@linux.intel.com wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> 
> On VLV/CHV the panel power sequencer may need to be "kicked" a bit to
> lock onto the new port, and that needs to happen before any aux
> transfers are attempted if we want the aux transfers to actaully
> succeed. So turn on panel power (part of the "kick") before aux
> transfers (DPMS_ON + link training).
> 
> This also matches the documented modeset sequence better for pch
> platforms. The documentation doesn't explicitly state anything about the
> DPMS or link training DPCD writes, but the panel power on step is
> always listed before link training is mentioned.
> 
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

Jani had the same change in:
https://bugs.freedesktop.org/show_bug.cgi?id=70117

which solved link training issues, so we could add a reference to that
bug and ask the reporters to retest. The patch looks ok:
Reviewed-by: Imre Deak <imre.deak@intel.com>

> ---
>  drivers/gpu/drm/i915/intel_dp.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index 4952783..28bc652 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -2275,10 +2275,10 @@ static void intel_enable_dp(struct intel_encoder *encoder)
>  		return;
>  
>  	intel_edp_panel_vdd_on(intel_dp);
> -	intel_dp_sink_dpms(intel_dp, DRM_MODE_DPMS_ON);
> -	intel_dp_start_link_train(intel_dp);
>  	intel_edp_panel_on(intel_dp);
>  	intel_edp_panel_vdd_off(intel_dp, true);
> +	intel_dp_sink_dpms(intel_dp, DRM_MODE_DPMS_ON);
> +	intel_dp_start_link_train(intel_dp);
>  	intel_dp_complete_link_train(intel_dp);
>  	intel_dp_stop_link_train(intel_dp);
>  }


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