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SubjectStill use ACPI backlight control if _DOS doesn't exist
Date
This is a regression introduced by commit
ea9f8856bd6d4ed45885b06a338f7362cd6c60e5

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

Some platforms don't have _DOS control method, but the ACPI
backlight still works.
We do not want to lose the backlight control ability on these platforms.

[airlied: this is breaking nouveau really badly on 3.4 and after and there is
no movement on sending it upstream, so please apply]

Cc: Igor Murzov <intergalactic.anonymous@gmail.com>
Cc: stable@vger.kernel.org
Cc: len.brown@intel.com
Signed-off-by: Zhang Rui <rui.zhang@intel.com>
---
drivers/acpi/video.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)

Index: rtd3/drivers/acpi/video.c
===================================================================
--- rtd3.orig/drivers/acpi/video.c
+++ rtd3/drivers/acpi/video.c
@@ -565,8 +565,14 @@ acpi_video_bus_DOS(struct acpi_video_bus
video->dos_setting = arg0.integer.value;
status = acpi_evaluate_object(video->device->handle, "_DOS",
&args, NULL);
- if (ACPI_FAILURE(status))
- return -EIO;
+ if (ACPI_FAILURE(status)) {
+ /*
+ * some platforms don't have _DOS, but the ACPI
+ * backlight control still works
+ */
+ ACPI_DEBUG_PRINT((ACPI_DB_INFO, "No _DOS\n"));
+ return 0;
+ }

return 0;
}

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