By default the PMIC DA9063 2-wire interface is SMBus compliant. This
means the PMIC will automatically reset the interface when the clock
signal ceases for more than the SMBus timeout of 35 ms.

If the I2C driver / device is not capable of creating atomic I2C
transactions, a context change can cause a ceasing of the clock signal.
This can happen if for example a real-time thread is scheduled. Then
the DA9063 in SMBus mode will reset the 2-wire interface. Subsequently
a write message could end up in the wrong register. This could cause
unpredictable system behavior.

The DA9063 PMIC also supports an I2C compliant mode for the 2-wire
interface. This mode does not reset the interface when the clock
signal ceases. Thus the problem depicted above does not occur.

This patch tests for the bus functionality "I2C_FUNC_I2C". It can
reasonably be assumed that the bus cannot obey SMBus timings if
this functionality is set. SMBus commands most probably are emulated
in this case which is prone to the latency issue described above.

This patch enables the I2C bus mode if I2C_FUNC_I2C is set or
otherwise keeps the default SMBus mode.
Signed-off-by: Hubert Streidl <hubert.streidl@de.bosch.com>
Signed-off-by: Mark Jonas <mark.jonas@de.bosch.com>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>