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

[Hans de Goede]

On 08-01-19 17:08, Maarten Lankhorst 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 at linux.intel.com>
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=108225
> Cc: Basil Eric Rabi <ericbasil.rabi at gmail.com>
> Cc: Hans de Goede <jwrdegoede at fedoraproject.org>
> Cc: Tolga Cakir <cevelnet at gmail.com>
> Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
> Tested-by: Tolga Cakir <cevelnet at gmail.com>
> Cc: Jani Nikula <jani.nikula at linux.intel.com>

Reviewed-by: Hans de Goede <hdegoede at redhat.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;
>   }
>