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

[Maarten Lankhorst]

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>
---
 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;
 }
-- 
2.20.1