Fix light sensor readings on newer MacBooks

The light sensors ALV0 and ALV1 on newer MacBooks (early 2008 and
later) changed to report 10 bytes instead the earlier 6, and the
sensor encoding subsequently changed. As a result, the reported light
sensors readings are much too low.

From experiments leading up to this patch, it seems only the ALV0 is
reporting data, and the most useful value therein is a 10-bit
big-endian value at offset 6. This suggests that a new protocol was
added as a backward-compatible replacement on top of the old one.

This patch makes applesmc report the improved light sensor reading for
the new machines, on a scale in conformance with earlier ones.

This patch has also been sent to kernel.org

Signed-off-by: Alex Murray <murray.alex@gmail.com>
Signed-off-by: Henrik Rydberg <rydberg@euromail.se>

1 files changed, 5 insertions, 0 deletions

diff --git a/usr/src/dkms_source_tree/applesmc.c b/usr/src/dkms_source_tree/applesmc.c
index acd818f..ebf4c03 100644
--- a/usr/src/dkms_source_tree/applesmc.c
+++ b/usr/src/dkms_source_tree/applesmc.c
@@ -590,6 +590,11 @@ static ssize_t applesmc_light_show(struct device *dev,
         }
 
         ret = applesmc_read_key(LIGHT_SENSOR_LEFT_KEY, buffer, data_length);
+        /* newer macbooks report a single 10-bit bigendian value */
+        if (data_length == 10) {
+                left = be16_to_cpu(*(__be16 *)(buffer + 6)) >> 2;
+                goto out;
+        }
         left = buffer[2];
         if (ret)
                 goto out;