[PATCH v4] drivers: i915: Default backlight PWM frequency

Simon Que
2011-11-11T22:13:07Z

If the firmware did not initialize the backlight PWM registers, set up a
default PWM frequency of 200 Hz. This is determined using the following
formula:

freq = refclk / (128 * pwm_max)

The PWM register allows the max PWM value to be set. So we want to use
the formula, where freq = 200:

pwm_max = refclk / (128 * freq)

This patch will, in the case of missing PWM register initialization
values, look for the reference clock frequency. Based on that, it sets
an appropriate max PWM value for a frequency of 200 Hz.

If no refclk frequency is found, the max PWM will be zero, which results
in no change to the PWM registers.

Signed-off-by: Simon Que <sque@chromium.org>
---
drivers/gpu/drm/i915/intel_panel.c | 38 ++++++++++++++++++++++++++++++-----
1 files changed, 32 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_panel.c b/drivers/gpu/drm/i915/intel_panel.c
index f15388c..dda5de2 100644
--- a/drivers/gpu/drm/i915/intel_panel.c
+++ b/drivers/gpu/drm/i915/intel_panel.c
@@ -32,6 +32,12 @@

#define PCI_LBPC 0xf4 /* legacy/combination backlight modes */

+/* These are used to calculate a reasonable default when firmware has not
+ * configured a maximum PWM frequency, with 200Hz as the current default target.
+ */
+#define DEFAULT_BACKLIGHT_PWM_FREQ 200
+#define BACKLIGHT_REFCLK_DIVISOR 128
+
void
intel_fixed_panel_mode(struct drm_display_mode *fixed_mode,
struct drm_display_mode *adjusted_mode)
@@ -129,12 +135,32 @@ static int is_backlight_combination_mode(struct drm_device *dev)
return 0;
}

+static void i915_set_default_max_backlight(struct drm_i915_private *dev_priv)
+{
+ u32 refclk_freq_mhz = 0;
+ u32 max_pwm;
+
+ if (HAS_PCH_SPLIT(dev_priv->dev))
+ refclk_freq_mhz = I915_READ(PCH_RAWCLK_FREQ) & RAWCLK_FREQ_MASK;
+ else if (dev_priv->lvds_use_ssc)
+ refclk_freq_mhz = dev_priv->lvds_ssc_freq;
+
+ max_pwm = refclk_freq_mhz * 1000000 /
+ (BACKLIGHT_REFCLK_DIVISOR * DEFAULT_BACKLIGHT_PWM_FREQ);
+
+ if (HAS_PCH_SPLIT(dev_priv->dev))
+ dev_priv->saveBLC_PWM_CTL2 = max_pwm << 16;
+ else if (IS_PINEVIEW(dev_priv->dev))
+ dev_priv->saveBLC_PWM_CTL = max_pwm << 17;
+ else
+ dev_priv->saveBLC_PWM_CTL = max_pwm << 16;
+}
+
static u32 i915_read_blc_pwm_ctl(struct drm_i915_private *dev_priv)
{
u32 val;

- /* Restore the CTL value if it lost, e.g. GPU reset */
-
+ /* Restore the CTL value if it was lost, e.g. GPU reset */
if (HAS_PCH_SPLIT(dev_priv->dev)) {
val = I915_READ(BLC_PWM_PCH_CTL2);
if (dev_priv->saveBLC_PWM_CTL2 == 0) {
@@ -168,11 +194,11 @@ u32 intel_panel_get_max_backlight(struct drm_device *dev)

max = i915_read_blc_pwm_ctl(dev_priv);
if (max == 0) {
- /* XXX add code here to query mode clock or hardware clock
- * and program max PWM appropriately.
+ /* If backlight PWM registers have not been set, set them to
+ * default backlight PWM settings.
*/
- printk_once(KERN_WARNING "fixme: max PWM is zero.\n");
- return 1;
+ i915_set_default_max_backlight(dev_priv);
+ max = i915_read_blc_pwm_ctl(dev_priv);
}

if (HAS_PCH_SPLIT(dev)) {
--
1.7.2.3