[Intel-gfx] [PATCH] drm/i915/dp: Write to SET_POWER dpcd to enable MST hub.

Ville Syrjälä ville.syrjala at linux.intel.com
Wed Mar 14 13:35:24 UTC 2018

On Tue, Mar 13, 2018 at 10:48:25PM -0700, Dhinakaran Pandiyan wrote:
> If bios sets up an MST output and hardware state readout code sees this is
> an SST configuration, when disabling the encoder we end up calling
> ->post_disable_dp() hook instead of the MST version. Consequently, we write
> to the DP_SET_POWER dpcd to set it D3 state. Further along when we try
> enable the encoder in MST mode, POWER_UP_PHY transaction fails to power up
> the MST hub. This results in continuous link training failures which keep
> the system busy delaying boot. We could identify bios MST boot discrepancy
> and handle it accordingly but a simple way to solve this is to write to the
> DP_SET_POWER dpcd for MST too.
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=105470
> Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
> Cc: Jani Nikula <jani.nikula at intel.com>
> Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan at intel.com>
> ---
>  drivers/gpu/drm/i915/intel_ddi.c | 7 ++-----
>  1 file changed, 2 insertions(+), 5 deletions(-)
> diff --git a/drivers/gpu/drm/i915/intel_ddi.c b/drivers/gpu/drm/i915/intel_ddi.c
> index dbcf1a0586f9..8c2d778560f0 100644
> --- a/drivers/gpu/drm/i915/intel_ddi.c
> +++ b/drivers/gpu/drm/i915/intel_ddi.c
> @@ -2205,8 +2205,7 @@ static void intel_ddi_pre_enable_dp(struct intel_encoder *encoder,
>  		intel_prepare_dp_ddi_buffers(encoder, crtc_state);
>  	intel_ddi_init_dp_buf_reg(encoder);
> -	if (!is_mst)
> -		intel_dp_sink_dpms(intel_dp, DRM_MODE_DPMS_ON);
> +	intel_dp_sink_dpms(intel_dp, DRM_MODE_DPMS_ON);

The spec is perhaps a bit unclear on this. 

"If the message is sent as a path request, all DP nodes from the source
 immediate downstream device and the targeted DP node will be placed in
 the D0 power state."

Doesn't quite tell me whether the immediate downstream device is
included in that list of nodes.

However the spec goes on to say
"Each nodes immediate upstream device will use Native AUX writes to the
 SET_POWER & SET_DP_PWR_VOLTAGE register (DPCD Address 00600h) to set
 the power state of the downstream node."

and since we are the immediate upstream for that device I guess it makes
sense that we should still do the DP_SET_POWER manually.

But I have to wonder what the original issue was before we started to use
POWER_UP/DOWN_PHY. I suppose somehow some further downstream device
wasn't in D0 when we needed it. But that is a bit weird as I believe all
devices should really start up in D0.

Anyways based on my reading of the spec I can justify this so
Reviewed-by: Ville Syrjälä <ville.syrjala at linux.intel.com>

I presume we want cc:stable + fixes: on this?

>  	intel_dp_start_link_train(intel_dp);
>  	if (port != PORT_A || INTEL_GEN(dev_priv) >= 9)
>  		intel_dp_stop_link_train(intel_dp);
> @@ -2304,14 +2303,12 @@ static void intel_ddi_post_disable_dp(struct intel_encoder *encoder,
>  	struct drm_i915_private *dev_priv = to_i915(encoder->base.dev);
>  	struct intel_digital_port *dig_port = enc_to_dig_port(&encoder->base);
>  	struct intel_dp *intel_dp = &dig_port->dp;
> -	bool is_mst = intel_crtc_has_type(old_crtc_state, INTEL_OUTPUT_DP_MST);
>  	/*
>  	 * Power down sink before disabling the port, otherwise we end
>  	 * up getting interrupts from the sink on detecting link loss.
>  	 */
> -	if (!is_mst)
> -		intel_dp_sink_dpms(intel_dp, DRM_MODE_DPMS_OFF);
> +	intel_dp_sink_dpms(intel_dp, DRM_MODE_DPMS_OFF);
>  	intel_disable_ddi_buf(encoder);
> -- 
> 2.14.1

Ville Syrjälä
Intel OTC

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