Re: [PATCH 2/2] drm/i915: Turn off g4x DP port in .post_disable()

[Jani Nikula <jani.nikula@linux.intel.com>]

On Wed, 13 Jun 2018, Ville Syrjala <ville.syrjala@linux.intel.com> wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
>
> While Bspec doesn't list a specific sequence for turning off the DP port
> on g4x we are getting an underrun if the port is disabled in the
> .disable() hook. Looks like the pipe stops when the port stops, and by
> that time the plane disable may not have completed yet. Also the plane(s)
> seem to end up in some wonky state when this happens as they also signal
> another underrun immediately after we turn them back on during the next
> enable sequence.
>
> We could add a vblank wait in .disable() to avoid wedging the planes,
> but I assume we're still tripping up the pipe in some way. So it seems
> better to me to just follow the ILK+ sequence and turn off the DP port
> in .post_disable() instead. This sequence doesn't seem to suffer from
> this problem. Could be it was always the intended sequence for DP and
> the gen4 bspec was just never updated to include it.
>
> Cc: stable@vger.kernel.org
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

The change for PCH was

commit 08aff3fe26ae7a0d6f302ac2e1b7e2eb9933cd42
Author: Ville Syrjälä <ville.syrjala@linux.intel.com>
Date:   Mon Aug 18 22:16:09 2014 +0300

    drm/i915: Move DP port disable to post_disable for pch platforms

where you explicitly left out g4x per modeset sequence. I guess you
could reference that in the commit message.

> ---
>  drivers/gpu/drm/i915/intel_dp.c | 26 +++++++++-----------------
>  1 file changed, 9 insertions(+), 17 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index 6068986fd985..5f09a8015c89 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -2803,16 +2803,6 @@ static void intel_disable_dp(struct intel_encoder *encoder,
>  static void g4x_disable_dp(struct intel_encoder *encoder,
>  			   const struct intel_crtc_state *old_crtc_state,
>  			   const struct drm_connector_state *old_conn_state)
> -{
> -	intel_disable_dp(encoder, old_crtc_state, old_conn_state);
> -
> -	/* disable the port before the pipe on g4x */
> -	intel_dp_link_down(encoder, old_crtc_state);
> -}
> -
> -static void ilk_disable_dp(struct intel_encoder *encoder,
> -			   const struct intel_crtc_state *old_crtc_state,
> -			   const struct drm_connector_state *old_conn_state)
>  {
>  	intel_disable_dp(encoder, old_crtc_state, old_conn_state);
>  }
> @@ -2828,13 +2818,19 @@ static void vlv_disable_dp(struct intel_encoder *encoder,
>  	intel_disable_dp(encoder, old_crtc_state, old_conn_state);
>  }
>  
> -static void ilk_post_disable_dp(struct intel_encoder *encoder,
> +static void g4x_post_disable_dp(struct intel_encoder *encoder,
>  				const struct intel_crtc_state *old_crtc_state,
>  				const struct drm_connector_state *old_conn_state)
>  {
>  	struct intel_dp *intel_dp = enc_to_intel_dp(&encoder->base);
>  	enum port port = encoder->port;
>  
> +	/*
> +	 * Bspec does not list a specific disable sequence for g4x DP.
> +	 * Follow the ilk+ sequence (disable pipe before the port) for
> +	 * g4x DP as it does not suffer from underruns like the normal
> +	 * g4x modeset sequence (disable pipe after the port).
> +	 */
>  	intel_dp_link_down(encoder, old_crtc_state);
>  
>  	/* Only ilk+ has port A */
> @@ -6450,15 +6446,11 @@ bool intel_dp_init(struct drm_i915_private *dev_priv,
>  		intel_encoder->enable = vlv_enable_dp;
>  		intel_encoder->disable = vlv_disable_dp;
>  		intel_encoder->post_disable = vlv_post_disable_dp;
> -	} else if (INTEL_GEN(dev_priv) >= 5) {
> -		intel_encoder->pre_enable = g4x_pre_enable_dp;
> -		intel_encoder->enable = g4x_enable_dp;
> -		intel_encoder->disable = ilk_disable_dp;
> -		intel_encoder->post_disable = ilk_post_disable_dp;
> -	} else {
> +	} else{

Space missing before {.

The code matches the commit message, so strictly in that sense,

Reviewed-by: Jani Nikula <jani.nikula@intel.com>

but I really don't know if this is the right thing to do. Your
call. (And your responsibility to fix the regressions! ;)


>  		intel_encoder->pre_enable = g4x_pre_enable_dp;
>  		intel_encoder->enable = g4x_enable_dp;
>  		intel_encoder->disable = g4x_disable_dp;
> +		intel_encoder->post_disable = g4x_post_disable_dp;
>  	}
>  
>  	intel_dig_port->dp.output_reg = output_reg;

-- 
Jani Nikula, Intel Open Source Graphics Center
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