Re: [PATCH 2/3] drm/i915: correct BLC vs PWM enable/disable ordering

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

On Mon, 31 Mar 2014, Jesse Barnes <jbarnes@virtuousgeek.org> wrote:
> With the new checks in place, we can see we're doing things backwards,
> so fix them up per the spec.
>
> Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
> ---
>  drivers/gpu/drm/i915/intel_dp.c | 13 +++++++------
>  1 file changed, 7 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index b6f7087..d540fbe 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -1273,8 +1273,6 @@ void intel_edp_panel_off(struct intel_dp *intel_dp)
>  
>  	DRM_DEBUG_KMS("Turn eDP power off\n");
>  
> -	edp_wait_backlight_off(intel_dp);
> -

Please justify moving this wait to intel_edp_backlight_off. I thought
the point of these wait calls is such that we'll only end up waiting
when we really have to. If this is left as-is, we can do useful stuff
*while* waiting (case in point, intel_dp_sink_dpms in intel_disable_dp).

Otherwise this looks good to me, although I didn't find proper
explanations for everything. Do I understand correctly that the
EDP_BLC_ENABLE bit in PP_CONTROL is basically the final switch for
enabling/disabling the PWM signal to the eDP? So before this patch, we
let the disabled PWM signal through to the panel?

BR,
Jani.


>  	WARN(!intel_dp->want_panel_vdd, "Need VDD to turn off panel\n");
>  
>  	/* By this time the PWM and BLC bits should be off already */
> @@ -1316,6 +1314,9 @@ void intel_edp_backlight_on(struct intel_dp *intel_dp)
>  		return;
>  
>  	DRM_DEBUG_KMS("\n");
> +
> +	intel_panel_enable_backlight(intel_dp->attached_connector);
> +
>  	/*
>  	 * If we enable the backlight right away following a panel power
>  	 * on, we may see slight flicker as the panel syncs with the eDP
> @@ -1333,8 +1334,6 @@ void intel_edp_backlight_on(struct intel_dp *intel_dp)
>  
>  	I915_WRITE(pp_ctrl_reg, pp);
>  	POSTING_READ(pp_ctrl_reg);
> -
> -	intel_panel_enable_backlight(intel_dp->attached_connector);
>  }
>  
>  void intel_edp_backlight_off(struct intel_dp *intel_dp)
> @@ -1350,8 +1349,6 @@ void intel_edp_backlight_off(struct intel_dp *intel_dp)
>  	/* PWM must still be enabled here */
>  	assert_pwm_enabled(intel_dp->attached_connector);
>  
> -	intel_panel_disable_backlight(intel_dp->attached_connector);
> -
>  	DRM_DEBUG_KMS("\n");
>  	pp = ironlake_get_pp_control(intel_dp);
>  	pp &= ~EDP_BLC_ENABLE;
> @@ -1361,6 +1358,10 @@ void intel_edp_backlight_off(struct intel_dp *intel_dp)
>  	I915_WRITE(pp_ctrl_reg, pp);
>  	POSTING_READ(pp_ctrl_reg);
>  	intel_dp->last_backlight_off = jiffies;
> +
> +	edp_wait_backlight_off(intel_dp);
> +
> +	intel_panel_disable_backlight(intel_dp->attached_connector);
>  }
>  
>  static void ironlake_edp_pll_on(struct intel_dp *intel_dp)
> -- 
> 1.8.4.2
>
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-- 
Jani Nikula, Intel Open Source Technology Center