commit: b03738430c7537d5f87948e0b35d8aaf2688c6b4
From: Zhang Rui <[email protected]>
Date: Wed, 20 Jun 2012 09:48:43 +0800
Subject: ACPI video: Still use ACPI backlight control if _DOS doesn't exist

This fixes a regression in 3.4-rc1 caused by commit
ea9f8856bd6d4ed45885b06a338f7362cd6c60e5
(ACPI video: Harden video bus adding.)

Some platforms don't have _DOS control method, but the ACPI
backlight still works.
We should not invoke _DOS for these platforms.

https://bugzilla.kernel.org/show_bug.cgi?id=43168

Cc: Igor Murzov <[email protected]>
Cc: [email protected]
Signed-off-by: Zhang Rui <[email protected]>
Signed-off-by: Len Brown <[email protected]>
---
 drivers/acpi/video.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/drivers/acpi/video.c b/drivers/acpi/video.c
index 9577b6f..4134b30 100644
--- a/drivers/acpi/video.c
+++ b/drivers/acpi/video.c
@@ -558,6 +558,8 @@ acpi_video_bus_DOS(struct acpi_video_bus *video, int 
bios_flag, int lcd_flag)
        union acpi_object arg0 = { ACPI_TYPE_INTEGER };
        struct acpi_object_list args = { 1, &arg0 };
 
+       if (!video->cap._DOS)
+               return 0;
 
        if (bios_flag < 0 || bios_flag > 3 || lcd_flag < 0 || lcd_flag > 1)
                return -EINVAL;
-- 
1.7.3.4
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