[PATCH] drm/i915 Trouble with minimum brightness

From: Jay Aurabind <mail@aurabindo.in>
To: Daniel Vetter <daniel.vetter@intel.com>,
	Jani Nikula <jani.nikula@linux.intel.com>,
	David Airlie <airlied@linux.ie>,
	intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org,
	linux-kernel@vger.kernel.org
Subject: [PATCH] drm/i915 Trouble with minimum brightness
Date: Sat, 29 Nov 2014 00:44:50 +0530	[thread overview]
Message-ID: <5478C9AA.2010600@aurabindo.in> (raw)

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Hello all,

I notice that some activity has been going on with the minimum value of display brightness recently (e1c412e7575).

But the minimum value thats currently chosen is not at all acceptable for my eyes. My display is working perfectly without that restriction on minimum intensity.
I tend to stare at the screen a lot and the current minimum settings is straining my eyes.

Even if you say that it may not be good for the devices, I still insist, because I want my *display* to fail first, not my eyes.
So please try providing a way for the needy users to override this minimum settings. I hope adding a module parameter would be easy fix.

Something like this: ? (I dont call myself a kernel programmer yet, just scratching the surface)


Provide provision for users to disable restriction on minimum brightness
value introduced in:

    commit e1c412e75754ab7b7002f3e18a2652d999c40d4b
    Author: Jani Nikula <jani.nikula@intel.com>
    Date:   Wed Nov 5 14:46:31 2014 +0200

        drm/i915: safeguard against too high minimum brightness

There are systems which work reliably without restriction on minimum
value of display brightness. Also the arbitrary value may be too high
for many users as well.

Signed-off-by: Aurabindo J <mail@aurabindo.in>
---
 drivers/gpu/drm/i915/i915_drv.h    |  1 +
 drivers/gpu/drm/i915/i915_params.c |  6 ++++++
 drivers/gpu/drm/i915/intel_panel.c | 14 ++++++++++----
 3 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 16a6f6d..55d2ead 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -2213,6 +2213,7 @@ struct i915_params {
 	int disable_power_well;
 	int enable_ips;
 	int invert_brightness;
+	int restrict_min_brightness;
 	int enable_cmd_parser;
 	/* leave bools at the end to not create holes */
 	bool enable_hangcheck;
diff --git a/drivers/gpu/drm/i915/i915_params.c b/drivers/gpu/drm/i915/i915_params.c
index c91cb20..0601c2a 100644
--- a/drivers/gpu/drm/i915/i915_params.c
+++ b/drivers/gpu/drm/i915/i915_params.c
@@ -46,6 +46,7 @@ struct i915_params i915 __read_mostly = {
 	.prefault_disable = 0,
 	.reset = true,
 	.invert_brightness = 0,
+	.restrict_min_brightness = 1,
 	.disable_display = 0,
 	.enable_cmd_parser = 1,
 	.disable_vtd_wa = 0,
@@ -155,6 +156,11 @@ MODULE_PARM_DESC(invert_brightness,
 	"to dri-devel@lists.freedesktop.org, if your machine needs it. "
 	"It will then be included in an upcoming module version.");

+module_param_named(restrict_min_brightness, i915.restrict_min_brightness, int, 0600);
+MODULE_PARM_DESC(restrict_min_brightness,
+	"Restrict minimum brightness "
+	"(-1 disable restriction, 0 value from VBT, 1 arbitrary value )");
+
 module_param_named(disable_display, i915.disable_display, bool, 0600);
 MODULE_PARM_DESC(disable_display, "Disable display (default: false)");

diff --git a/drivers/gpu/drm/i915/intel_panel.c b/drivers/gpu/drm/i915/intel_panel.c
index 41b3be2..def9f4e 100644
--- a/drivers/gpu/drm/i915/intel_panel.c
+++ b/drivers/gpu/drm/i915/intel_panel.c
@@ -1109,10 +1109,16 @@ static u32 get_backlight_min_vbt(struct intel_connector *connector)
 	 * against this by letting the minimum be at most (arbitrarily chosen)
 	 * 25% of the max.
 	 */
-	min = clamp_t(int, dev_priv->vbt.backlight.min_brightness, 0, 64);
-	if (min != dev_priv->vbt.backlight.min_brightness) {
-		DRM_DEBUG_KMS("clamping VBT min backlight %d/255 to %d/255\n",
-			      dev_priv->vbt.backlight.min_brightness, min);
+	if (i915.restrict_min_brightness < 0)
+		min = 0;
+	else if (i915.restrict_min_brightness == 0)
+		min = dev_priv->vbt.backlight.min_brightness;
+	else {
+		min = clamp_t(int, dev_priv->vbt.backlight.min_brightness, 0, 64);
+		if (min != dev_priv->vbt.backlight.min_brightness) {
+			DRM_DEBUG_KMS("clamping VBT min backlight %d/255 to %d/255\n",
+					dev_priv->vbt.backlight.min_brightness, min);
+	    }
 	}

 	/* vbt value is a coefficient in range [0..255] */
-- 
2.1.3






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