Re: [PATCH 2/5] drm/i915/backlight: Fix backlight takeover on LPT, v3.

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

On Tue, 08 Jan 2019, Maarten Lankhorst <maarten.lankhorst@linux.intel.com> wrote:
> On lynxpoint the bios sometimes sets up the backlight using the CPU
> display, but the driver expects using the PWM PCH override register.
>
> Read the value from the CPU register, then convert it to the other
> units by converting from the old duty cycle, to freq, to the new units.
>
> This value is then programmed in the override register, after which
> we set the override and disable the CPU display control. This allows
> us to switch the source without flickering, and make the backlight
> controls work in the driver.
>
> Changes since v1:
> - Read BLC_PWM_CPU_CTL2 to cpu_ctl2.
> - Clean up cpu_mode if slightly.
> - Always disable BLM_PWM_ENABLE in cpu_ctl2.
> Changes since v2:
> - Simplify cpu_mode handling (Jani)
>
> Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=108225
> Cc: Basil Eric Rabi <ericbasil.rabi@gmail.com>
> Cc: Hans de Goede <jwrdegoede@fedoraproject.org>
> Cc: Tolga Cakir <cevelnet@gmail.com>
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Tested-by: Tolga Cakir <cevelnet@gmail.com>
> Cc: Jani Nikula <jani.nikula@linux.intel.com>

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

> ---
>  drivers/gpu/drm/i915/intel_panel.c | 26 ++++++++++++++++++++++----
>  1 file changed, 22 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_panel.c b/drivers/gpu/drm/i915/intel_panel.c
> index f71b33cf1c97..1c9ef54d58fe 100644
> --- a/drivers/gpu/drm/i915/intel_panel.c
> +++ b/drivers/gpu/drm/i915/intel_panel.c
> @@ -1493,8 +1493,8 @@ static int lpt_setup_backlight(struct intel_connector *connector, enum pipe unus
>  {
>  	struct drm_i915_private *dev_priv = to_i915(connector->base.dev);
>  	struct intel_panel *panel = &connector->panel;
> -	u32 pch_ctl1, pch_ctl2, val;
> -	bool alt;
> +	u32 cpu_ctl2, pch_ctl1, pch_ctl2, val;
> +	bool alt, cpu_mode;
>  
>  	if (HAS_PCH_LPT(dev_priv))
>  		alt = I915_READ(SOUTH_CHICKEN2) & LPT_PWM_GRANULARITY;
> @@ -1508,6 +1508,8 @@ static int lpt_setup_backlight(struct intel_connector *connector, enum pipe unus
>  	pch_ctl2 = I915_READ(BLC_PWM_PCH_CTL2);
>  	panel->backlight.max = pch_ctl2 >> 16;
>  
> +	cpu_ctl2 = I915_READ(BLC_PWM_CPU_CTL2);
> +
>  	if (!panel->backlight.max)
>  		panel->backlight.max = get_backlight_max_vbt(connector);
>  
> @@ -1516,12 +1518,28 @@ static int lpt_setup_backlight(struct intel_connector *connector, enum pipe unus
>  
>  	panel->backlight.min = get_backlight_min_vbt(connector);
>  
> -	val = lpt_get_backlight(connector);
> +	panel->backlight.enabled = pch_ctl1 & BLM_PCH_PWM_ENABLE;
> +
> +	cpu_mode = panel->backlight.enabled && HAS_PCH_LPT(dev_priv) &&
> +		   !(pch_ctl1 & BLM_PCH_OVERRIDE_ENABLE) &&
> +		   (cpu_ctl2 & BLM_PWM_ENABLE);
> +	if (cpu_mode)
> +		val = pch_get_backlight(connector);
> +	else
> +		val = lpt_get_backlight(connector);
>  	val = intel_panel_compute_brightness(connector, val);
>  	panel->backlight.level = clamp(val, panel->backlight.min,
>  				       panel->backlight.max);
>  
> -	panel->backlight.enabled = pch_ctl1 & BLM_PCH_PWM_ENABLE;
> +	if (cpu_mode) {
> +		DRM_DEBUG_KMS("CPU backlight register was enabled, switching to PCH override\n");
> +
> +		/* Write converted CPU PWM value to PCH override register */
> +		lpt_set_backlight(connector->base.state, panel->backlight.level);
> +		I915_WRITE(BLC_PWM_PCH_CTL1, pch_ctl1 | BLM_PCH_OVERRIDE_ENABLE);
> +
> +		I915_WRITE(BLC_PWM_CPU_CTL2, cpu_ctl2 & ~BLM_PWM_ENABLE);
> +	}
>  
>  	return 0;
>  }

-- 
Jani Nikula, Intel Open Source Graphics Center
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