drm/i915: Refactor panel backlight controls

There were two instances of code to control the panel backlight and
neither handled the complete set of device variations.

Fixes:

  Bug 29716 - [GM965] Regression: Backlight resets to minimum when changing resolution
  https://bugs.freedesktop.org/show_bug.cgi?id=29716

And a bug on one of my PineView boxes which overflowed the backlight
value.

Incorporates part of a similar patch by Matthew Garrett that exposes a
native Intel backlight controller.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

1 files changed, 109 insertions, 0 deletions

diff --git a/drivers/gpu/drm/i915/intel_panel.c b/drivers/gpu/drm/i915/intel_panel.c
index e7f5299d9d5..30abe7afc94 100644
--- a/drivers/gpu/drm/i915/intel_panel.c
+++ b/drivers/gpu/drm/i915/intel_panel.c
@@ -30,6 +30,8 @@
 
 #include "intel_drv.h"
 
+#define PCI_LBPC 0xf4 /* legacy/combination backlight modes */
+
 void
 intel_fixed_panel_mode(struct drm_display_mode *fixed_mode,
 		       struct drm_display_mode *adjusted_mode)
@@ -109,3 +111,110 @@ done:
 	dev_priv->pch_pf_pos = (x << 16) | y;
 	dev_priv->pch_pf_size = (width << 16) | height;
 }
+
+static int is_backlight_combination_mode(struct drm_device *dev)
+{
+	struct drm_i915_private *dev_priv = dev->dev_private;
+
+	if (IS_I965G(dev))
+		return I915_READ(BLC_PWM_CTL2) & BLM_COMBINATION_MODE;
+
+	if (IS_GEN2(dev))
+		return I915_READ(BLC_PWM_CTL) & BLM_LEGACY_MODE;
+
+	return 0;
+}
+
+u32 intel_panel_get_max_backlight(struct drm_device *dev)
+{
+	struct drm_i915_private *dev_priv = dev->dev_private;
+	u32 max;
+
+	if (HAS_PCH_SPLIT(dev)) {
+		max = I915_READ(BLC_PWM_PCH_CTL2) >> 16;
+	} else {
+		max = I915_READ(BLC_PWM_CTL);
+		if (IS_PINEVIEW(dev)) {
+			max >>= 17;
+		} else {
+			max >>= 16;
+			if (!IS_I965G(dev))
+				max &= ~1;
+		}
+
+		if (is_backlight_combination_mode(dev))
+			max *= 0xff;
+	}
+
+	if (max == 0) {
+		/* XXX add code here to query mode clock or hardware clock
+		 * and program max PWM appropriately.
+		 */
+		DRM_ERROR("fixme: max PWM is zero.\n");
+		max = 1;
+	}
+
+	DRM_DEBUG_DRIVER("max backlight PWM = %d\n", max);
+	return max;
+}
+
+u32 intel_panel_get_backlight(struct drm_device *dev)
+{
+	struct drm_i915_private *dev_priv = dev->dev_private;
+	u32 val;
+
+	if (HAS_PCH_SPLIT(dev)) {
+		val = I915_READ(BLC_PWM_CPU_CTL) & BACKLIGHT_DUTY_CYCLE_MASK;
+	} else {
+		val = I915_READ(BLC_PWM_CTL) & BACKLIGHT_DUTY_CYCLE_MASK;
+		if (IS_PINEVIEW(dev))
+			val >>= 1;
+
+		if (is_backlight_combination_mode(dev)){
+			u8 lbpc;
+
+			val &= ~1;
+			pci_read_config_byte(dev->pdev, PCI_LBPC, &lbpc);
+			val *= lbpc;
+			val >>= 1;
+		}
+	}
+
+	DRM_DEBUG_DRIVER("get backlight PWM = %d\n", val);
+	return val;
+}
+
+static void intel_pch_panel_set_backlight(struct drm_device *dev, u32 level)
+{
+	struct drm_i915_private *dev_priv = dev->dev_private;
+	u32 val = I915_READ(BLC_PWM_CPU_CTL) & ~BACKLIGHT_DUTY_CYCLE_MASK;
+	I915_WRITE(BLC_PWM_CPU_CTL, val | level);
+}
+
+void intel_panel_set_backlight(struct drm_device *dev, u32 level)
+{
+	struct drm_i915_private *dev_priv = dev->dev_private;
+	u32 tmp;
+
+	DRM_DEBUG_DRIVER("set backlight PWM = %d\n", level);
+
+	if (HAS_PCH_SPLIT(dev))
+		return intel_pch_panel_set_backlight(dev, level);
+
+	if (is_backlight_combination_mode(dev)){
+		u32 max = intel_panel_get_max_backlight(dev);
+		u8 lpbc;
+
+		lpbc = level * 0xfe / max + 1;
+		level /= lpbc;
+		pci_write_config_byte(dev->pdev, PCI_LBPC, lpbc);
+	}
+
+	tmp = I915_READ(BLC_PWM_CTL);
+	if (IS_PINEVIEW(dev)) {
+		tmp &= ~(BACKLIGHT_DUTY_CYCLE_MASK - 1);
+		level <<= 1;
+	} else
+		tmp &= ~BACKLIGHT_DUTY_CYCLE_MASK;
+	I915_WRITE(BLC_PWM_CTL, tmp | level);
+}