Compared to the earlier TI SoCs, am65 has an additional level of dedicated
multiplexing registers for the timer IO pads.

There are timer IO pads in the MCU domain, and in the MAIN domain. These
pads can be muxed for the related timers.

There are timer IO control registers for input and output. The registers
for CTRLMMR_TIMER*_CTRL and CTRLMMR_MCU_TIMER*_CTRL are used to control
the input. The registers for CTCTRLMMR_TIMERIO*_CTRL and
CTRLMMR_MCU_TIMERIO*_CTRL the output.

The multiplexing is documented in TRM "5.1.2.3.1.4 Timer IO Muxing Control
Registers" and "5.1.3.3.1.5 Timer IO Muxing Control Registers", and the
CASCADE_EN bit is documented in TRM "12.8.3.1 Timers Overview".

For chaining timers, the timer IO control registers also have a CASCADE_EN
input bit in the CTRLMMR_TIMER*_CTRL in the registers. The CASCADE_EN bit
muxes the previous timer output, or possibly and external TIMER_IO pad
source, to the input clock of the selected timer instance for odd numered
timers. For the even numbered timers, the CASCADE_EN bit does not do
anything. The timer cascade input routing options are shown in TRM
"Figure 12-3632. Timers Overview". For handling beyond multiplexing, the
driver support for timer cascading should be likely be handled via the
clock framework.

Cc: Keerthy <j-keerthy@ti.com>
Cc: Nishanth Menon <nm@ti.com>
Cc: Vignesh Raghavendra <vigneshr@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Nishanth Menon <nm@ti.com>
Link: https://lore.kernel.org/r/20221115154842.7755-2-tony@atomide.com