i2c: bcm2835: Model Divider in CCF

i2c: bcm2835: Model Divider in CCF

Model the I2C bus clock divider as a part of the Core Clock Framework.
Primarily this removes the clk_get_rate() call from each transfer.
This call causes problems for slave drivers that themselves have
internal clock components that are controlled by an I2C interface.
When the slave's internal clock component is prepared, the prepare
lock is obtained, and it makes calls to the I2C subsystem to
command the hardware to activate the clock.  In order to perform
the I2C transfer, this driver sets the divider, which requires
it to get the parent clock rate, which it does with clk_get_rate().
Unfortunately, this function will try to take the clock prepare
lock, which is already held by the slave's internal clock calls
creating a deadlock.

Modeling the divider in the CCF natively removes this dependency
and the divider value is only set upon changing the bus clock
frequency or changes in the parent clock that cascade down to this
divisor.  This obviates the need to set the divider with every
transfer and avoids the deadlock described above.  It also should
provide better clock debugging and save a few cycles on each
transfer due to not having to recalcuate the divider value.

Signed-off-by: Annaliese McDermond <nh6z@nh6z.net>
Acked-by: Stefan Wahren <stefan.wahren@i2se.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>