Re: [PATCH 1/3] drm/i915: add PWM and BLC assertion checks

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

On Mon, 31 Mar 2014, Jesse Barnes <jbarnes@virtuousgeek.org> wrote:
> To make sure we properly follow the enable/disable sequences.
>
> Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
> ---
>  drivers/gpu/drm/i915/intel_dp.c    | 62 ++++++++++++++++++++++++++++++++++++--
>  drivers/gpu/drm/i915/intel_drv.h   |  1 +
>  drivers/gpu/drm/i915/intel_panel.c |  5 ++-
>  3 files changed, 65 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index bf73771..b6f7087 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -301,6 +301,20 @@ static u32 _pp_stat_reg(struct intel_dp *intel_dp)
>  		return VLV_PIPE_PP_STATUS(vlv_power_sequencer_pipe(intel_dp));
>  }
>  
> +static void assert_pwm(struct intel_connector *connector,
> +		       bool expected_state)
> +{
> +	bool state;
> +
> +	state = intel_panel_get_backlight(connector);

If the duty cycle is regarded as a binary on/off, I'd rather add an
additional "is enabled" call to intel_panel.c. Especially so because the
duty cycle value returned by intel_panel_get_backlight is meaningless
without the max value.

> +
> +	WARN(state != expected_state, "pwm state failure, expected %d, found "
> +	     "%d\n", expected_state, state);
> +}
> +
> +#define assert_pwm_enabled(c) assert_pwm((c), true)
> +#define assert_pwm_disabled(c) assert_pwm((c), false)
> +
>  static bool edp_have_panel_power(struct intel_dp *intel_dp)
>  {
>  	struct drm_device *dev = intel_dp_to_dev(intel_dp);
> @@ -884,6 +898,8 @@ static void intel_dp_mode_set(struct intel_encoder *encoder)
>  	struct intel_crtc *crtc = to_intel_crtc(encoder->base.crtc);
>  	struct drm_display_mode *adjusted_mode = &crtc->config.adjusted_mode;
>  
> +	assert_pwm_disabled(intel_dp->attached_connector);
> +
>  	/*
>  	 * There are four kinds of DP registers:
>  	 *
> @@ -1167,6 +1183,23 @@ static void edp_panel_vdd_off(struct intel_dp *intel_dp, bool sync)
>  	}
>  }
>  
> +/*
> + * For this and the disable sequence below, Google for actual eDP LCD timing
> + * diagrams or check the eDP spec.  Below is for reference on asserts and
> + * does not contain Tx values for delays between steps.
> + *
> + * For panel on, the sequence should be:
> + * - LCD power supply on (PP regs or VDD AUX)
> + *   - eDP should display black at this point
> + * - HPD (if present) should go high
> + * - AUX channel becomes available
> + * - link training begins
> + * - LED backlight power on
> + * - LED PWM_EN goes high, duty cycle >min (PWM regs)
> + * - link training completes
> + * - LED_EN goes high (PP BLC_EN bit)
> + */
> +
>  void intel_edp_panel_on(struct intel_dp *intel_dp)
>  {
>  	struct drm_device *dev = intel_dp_to_dev(intel_dp);
> @@ -1212,6 +1245,19 @@ void intel_edp_panel_on(struct intel_dp *intel_dp)
>  	}
>  }
>  
> +/*
> + * For panel off the sequence should be:
> + * - LED_EN goes low (BLC_EN in our PP regs)
> + * - LED PWM_EN goes low (PWM duty cycle 0 and PWM enable = 0)
> + *   - eDP should display black video at this point
> + * - LED VCCS goes low (power for backlight)
> + * - DP link goes to idle or off
> + * - AUX goes down
> + * - HPD line (if present) drops to low
> + * - eDP black video stops
> + * - LCD power supply shuts down (PP regs and VDD AUX)
> + */
> +
>  void intel_edp_panel_off(struct intel_dp *intel_dp)
>  {
>  	struct intel_digital_port *intel_dig_port = dp_to_dig_port(intel_dp);
> @@ -1231,11 +1277,17 @@ void intel_edp_panel_off(struct intel_dp *intel_dp)
>  
>  	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 */
> +	assert_pwm_disabled(intel_dp->attached_connector);
> +
>  	pp = ironlake_get_pp_control(intel_dp);
> +
> +	WARN(pp & EDP_BLC_ENABLE,
> +	     "backlight controller still on at panel off time\n");
> +
>  	/* We need to switch off panel power _and_ force vdd, for otherwise some
>  	 * panels get very unhappy and cease to work. */
> -	pp &= ~(POWER_TARGET_ON | PANEL_POWER_RESET | EDP_FORCE_VDD |
> -		EDP_BLC_ENABLE);
> +	pp &= ~(POWER_TARGET_ON | PANEL_POWER_RESET | EDP_FORCE_VDD);
>  
>  	pp_ctrl_reg = _pp_ctrl_reg(intel_dp);
>  
> @@ -1271,6 +1323,9 @@ void intel_edp_backlight_on(struct intel_dp *intel_dp)
>  	 * allowing it to appear.
>  	 */
>  	wait_backlight_on(intel_dp);
> +
> +	assert_pwm_enabled(intel_dp->attached_connector);
> +
>  	pp = ironlake_get_pp_control(intel_dp);
>  	pp |= EDP_BLC_ENABLE;
>  
> @@ -1292,6 +1347,9 @@ void intel_edp_backlight_off(struct intel_dp *intel_dp)
>  	if (!is_edp(intel_dp))
>  		return;
>  
> +	/* 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");
> diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
> index 9002e77..0e91c40 100644
> --- a/drivers/gpu/drm/i915/intel_drv.h
> +++ b/drivers/gpu/drm/i915/intel_drv.h
> @@ -861,6 +861,7 @@ void intel_gmch_panel_fitting(struct intel_crtc *crtc,
>  			      int fitting_mode);
>  void intel_panel_set_backlight(struct intel_connector *connector, u32 level,
>  			       u32 max);
> +u32 intel_panel_get_backlight(struct intel_connector *connector);
>  int intel_panel_setup_backlight(struct drm_connector *connector);
>  void intel_panel_enable_backlight(struct intel_connector *connector);
>  void intel_panel_disable_backlight(struct intel_connector *connector);
> diff --git a/drivers/gpu/drm/i915/intel_panel.c b/drivers/gpu/drm/i915/intel_panel.c
> index cb05840..21c5e6f 100644
> --- a/drivers/gpu/drm/i915/intel_panel.c
> +++ b/drivers/gpu/drm/i915/intel_panel.c
> @@ -384,6 +384,9 @@ static u32 _vlv_get_backlight(struct drm_device *dev, enum pipe pipe)
>  {
>  	struct drm_i915_private *dev_priv = dev->dev_private;
>  
> +	if (I915_READ(VLV_BLC_PWM_CTL2(pipe) & BLM_PWM_ENABLE))
> +		return 0;
> +

If our internal state is consistent, I don't think this should be
necessary. And if our internal state isn't consistent, we should fix
that and maybe add internal asserts within intel_panel.c.

>  	return I915_READ(VLV_BLC_PWM_CTL(pipe)) & BACKLIGHT_DUTY_CYCLE_MASK;
>  }
>  
> @@ -395,7 +398,7 @@ static u32 vlv_get_backlight(struct intel_connector *connector)
>  	return _vlv_get_backlight(dev, pipe);
>  }
>  
> -static u32 intel_panel_get_backlight(struct intel_connector *connector)
> +u32 intel_panel_get_backlight(struct intel_connector *connector)
>  {
>  	struct drm_device *dev = connector->base.dev;
>  	struct drm_i915_private *dev_priv = dev->dev_private;
> -- 
> 1.8.4.2
>
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-- 
Jani Nikula, Intel Open Source Technology Center