hwmon: (applesmc) Always read until end of data
commit 25f2bd7f upstream. The crash reported and investigated in commit 5f4513 turned out to be caused by a change to the read interface on newer (2012) SMCs. Tests by Chris show that simply reading the data valid line is enough for the problem to go away. Additional tests show that the newer SMCs no longer wait for the number of requested bytes, but start sending data right away. Apparently the number of bytes to read is no longer specified as before, but instead found out by reading until end of data. Failure to read until end of data confuses the state machine, which eventually causes the crash. As a remedy, assuming bit0 is the read valid line, make sure there is nothing more to read before leaving the read function. Tested to resolve the original problem, and runtested on MBA3,1, MBP4,1, MBP8,2, MBP10,1, MBP10,2. The patch seems to have no effect on machines before 2012. Tested-by: Chris Murphy <chris@cmurf.com> Signed-off-by: Henrik Rydberg <rydberg@euromail.se> Signed-off-by: Guenter Roeck <linux@roeck-us.net> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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