[Intel-gfx] [PATCH] drm/i915: Allow user to override PWM backlight frequency and duty cycle

[Alex Ivanov]

Since vendor may set bad defaults or user just generally may prefer her health over
display life.
1. Allow overriding of PWM frequency otherwise people use solutions like
http://devbraindom.blogspot.ru/2013/03/eliminate-led-screen-flicker-with-intel.html
which are bad because
I. frequency convertation logic varies from chip to chip, so people set totally wrong
frequences in most cases
II. writing to backlight control registers directly goes into conflict with
i915 driver doing the same
2. Allow to override minimal brightness. Even if vendor limit was totally correct,
it may be too bright to use in night, plus the default will become most likely wrong
now, since frequency was overriden

---
 drivers/gpu/drm/i915/i915_params.c |  6 ++++++
 drivers/gpu/drm/i915/i915_params.h |  2 ++
 drivers/gpu/drm/i915/intel_panel.c | 17 +++++++++++++++++
 3 files changed, 25 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_params.c b/drivers/gpu/drm/i915/i915_params.c
index b4faeb6aa2bd..ba37257846b0 100644
--- a/drivers/gpu/drm/i915/i915_params.c
+++ b/drivers/gpu/drm/i915/i915_params.c
@@ -190,3 +190,9 @@ i915_param_named(enable_dpcd_backlight, bool, 0600,
 
 i915_param_named(enable_gvt, bool, 0400,
 	"Enable support for Intel GVT-g graphics virtualization host support(default:false)");
+
+i915_param_named_unsafe(backlight_freq, uint, 0400,
+	"Override PWM backlight frequency (set in Hz, 0=ignore [default])");
+
+i915_param_named_unsafe(backlight_min_level, uint, 0400,
+	"Override PWM backlight minimum level (duty cycle, 0=ignore [default])");
diff --git a/drivers/gpu/drm/i915/i915_params.h b/drivers/gpu/drm/i915/i915_params.h
index c7292268ed43..7aba85db3da2 100644
--- a/drivers/gpu/drm/i915/i915_params.h
+++ b/drivers/gpu/drm/i915/i915_params.h
@@ -53,6 +53,8 @@
 	param(int, edp_vswing, 0) \
 	param(int, reset, 2) \
 	param(unsigned int, inject_load_failure, 0) \
+	param(unsigned int, backlight_freq, 0) \
+	param(unsigned int, backlight_min_level, 0) \
 	/* leave bools at the end to not create holes */ \
 	param(bool, alpha_support, IS_ENABLED(CONFIG_DRM_I915_ALPHA_SUPPORT)) \
 	param(bool, enable_cmd_parser, true) \
diff --git a/drivers/gpu/drm/i915/intel_panel.c b/drivers/gpu/drm/i915/intel_panel.c
index adc51e452e3e..f188d7c1d2de 100644
--- a/drivers/gpu/drm/i915/intel_panel.c
+++ b/drivers/gpu/drm/i915/intel_panel.c
@@ -1479,6 +1479,12 @@ static u32 get_backlight_min_vbt(struct intel_connector *connector)
 
 	WARN_ON(panel->backlight.max == 0);
 
+	if (i915_modparams.backlight_min_level) {
+		DRM_DEBUG_KMS("Override backlight duty cycle %u\n",
+						i915_modparams.backlight_min_level);
+		return i915_modparams.backlight_min_level;
+	}
+
 	/*
 	 * XXX: If the vbt value is 255, it makes min equal to max, which leads
 	 * to problems. There are such machines out there. Either our
@@ -1795,6 +1801,7 @@ int intel_panel_setup_backlight(struct drm_connector *connector, enum pipe pipe)
 	struct intel_connector *intel_connector = to_intel_connector(connector);
 	struct intel_panel *panel = &intel_connector->panel;
 	int ret;
+	u32 pwm;
 
 	if (!dev_priv->vbt.backlight.present) {
 		if (dev_priv->quirks & QUIRK_BACKLIGHT_PRESENT) {
@@ -1812,6 +1819,16 @@ int intel_panel_setup_backlight(struct drm_connector *connector, enum pipe pipe)
 	/* set level and max in panel struct */
 	mutex_lock(&dev_priv->backlight_lock);
 	ret = panel->backlight.setup(intel_connector, pipe);
+	if (i915_modparams.backlight_freq) {
+		if (panel->backlight.hz_to_pwm &&
+				(pwm = panel->backlight.hz_to_pwm(intel_connector, i915_modparams.backlight_freq))) {
+			panel->backlight.max = pwm;
+			DRM_DEBUG_KMS("Override backlight frequency %u Hz\n",
+							i915_modparams.backlight_freq);
+		} else {
+			DRM_DEBUG_KMS("failed to override backlight frequency\n");
+		}
+	}
 	mutex_unlock(&dev_priv->backlight_lock);
 
 	if (ret) {
-- 
2.15.1