From: Hans de Goede <hdegoede@redhat.com>
Date: Fri, 9 Jan 2015 14:51:21 +0100
Subject: [PATCH] samsung-laptop: Add use_native_backlight quirk, and enable it
 on some models

Since kernel 3.14 the backlight control has been broken on various Samsung
Atom based netbooks. This has been bisected and this problem happens since
commit b35684b8fa94 ("drm/i915: do full backlight setup at enable time")

This has been reported and discussed in detail here:
http://lists.freedesktop.org/archives/intel-gfx/2014-July/049395.html

Unfortunately no-one has been able to fix this. This only affects Samsung
Atom netbooks, and the Linux kernel and the BIOS of those laptops have never
worked well together. All affected laptops already have a quirk to avoid using
the standard acpi-video interface and instead use the samsung specific SABI
interface which samsung-laptop uses. It seems that recent fixes to the i915
driver have also broken backlight control through the SABI interface.

The intel_backlight driver OTOH works fine, and also allows for finer grained
backlight control. So add a new use_native_backlight quirk, and replace the
broken_acpi_video quirk with this quirk for affected models. This new quirk
disables acpi-video as before and also stops samsung-laptop from registering
the SABI based samsung_laptop backlight interface, leaving only the working
intel_backlight interface.

This commit enables this new quirk for 3 models which are known to be affected,
chances are that it needs to be used on other models too.

BugLink: https://bugzilla.redhat.com/show_bug.cgi?id=1094948 # N145P
BugLink: https://bugzilla.redhat.com/show_bug.cgi?id=1115713 # N250P
Reported-by: Bertrik Sikken <bertrik@sikken.nl> # N150P
Cc: stable@vger.kernel.org # 3.16
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
---
 drivers/platform/x86/samsung-laptop.c | 20 +++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/drivers/platform/x86/samsung-laptop.c b/drivers/platform/x86/samsung-laptop.c
index 864290243e46..477de0a9e1ee 100644
--- a/drivers/platform/x86/samsung-laptop.c
+++ b/drivers/platform/x86/samsung-laptop.c
@@ -353,6 +353,7 @@ struct samsung_quirks {
 	bool broken_acpi_video;
 	bool four_kbd_backlight_levels;
 	bool enable_kbd_backlight;
+	bool use_native_backlight;
 };
 
 static struct samsung_quirks samsung_unknown = {};
@@ -361,6 +362,10 @@ static struct samsung_quirks samsung_broken_acpi_video = {
 	.broken_acpi_video = true,
 };
 
+static struct samsung_quirks samsung_use_native_backlight = {
+	.use_native_backlight = true,
+};
+
 static struct samsung_quirks samsung_np740u3e = {
 	.four_kbd_backlight_levels = true,
 	.enable_kbd_backlight = true,
@@ -1507,7 +1512,7 @@ static struct dmi_system_id __initdata samsung_dmi_table[] = {
 		DMI_MATCH(DMI_PRODUCT_NAME, "N150P"),
 		DMI_MATCH(DMI_BOARD_NAME, "N150P"),
 		},
-	 .driver_data = &samsung_broken_acpi_video,
+	 .driver_data = &samsung_use_native_backlight,
 	},
 	{
 	 .callback = samsung_dmi_matched,
@@ -1517,7 +1522,7 @@ static struct dmi_system_id __initdata samsung_dmi_table[] = {
 		DMI_MATCH(DMI_PRODUCT_NAME, "N145P/N250P/N260P"),
 		DMI_MATCH(DMI_BOARD_NAME, "N145P/N250P/N260P"),
 		},
-	 .driver_data = &samsung_broken_acpi_video,
+	 .driver_data = &samsung_use_native_backlight,
 	},
 	{
 	 .callback = samsung_dmi_matched,
@@ -1557,7 +1562,7 @@ static struct dmi_system_id __initdata samsung_dmi_table[] = {
 		DMI_MATCH(DMI_PRODUCT_NAME, "N250P"),
 		DMI_MATCH(DMI_BOARD_NAME, "N250P"),
 		},
-	 .driver_data = &samsung_broken_acpi_video,
+	 .driver_data = &samsung_use_native_backlight,
 	},
 	{
 	 .callback = samsung_dmi_matched,
@@ -1626,6 +1631,15 @@ static int __init samsung_init(void)
 		pr_info("Disabling ACPI video driver\n");
 		acpi_video_unregister();
 	}
+
+	if (samsung->quirks->use_native_backlight) {
+		pr_info("Using native backlight driver\n");
+		/* Tell acpi-video to not handle the backlight */
+		acpi_video_dmi_promote_vendor();
+		acpi_video_unregister();
+		/* And also do not handle it ourselves */
+		samsung->handle_backlight = false;
+	}
 #endif
 
 	ret = samsung_platform_init(samsung);
-- 
2.1.0