The default value of the maximum fan speed limit register is 0,
essentially translating to an unlimited fan speed. When reading
the limit, a value of 0 is reported in this case. However, writing
a value of 0 results in writing a value of 0xffff into the register,
which is inconsistent.
To solve the problem, permit writing a limit of 0 for the maximim fan
speed, effectively translating to "no limit". Write 0 into the register
if a limit value of 0 is written. Otherwise limit the range to
<1..6000000> and write 1..0xffff into the register. This ensures that
reading and writing from and to a limit register return the same value
while at the same time not changing reported values when reading the
speed or limits.
While at it, restrict fan limit writes to non-negative numbers; writing
a negative limit does not make sense and should be reported instead of
being corrected.
Reviewed-by: Quentin Schulz <quentin.schulz@cherry.de>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
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