• Tony Lindgren's avatar
    Documentation: dt-bindings: Add binding documentation for TI clkctrl clocks · 35395a9c
    Tony Lindgren authored
    Texas Instruments omap variant SoCs starting with omap4 have a clkctrl
    clock controller instance for each interconnect target module. The clkctrl
    controls functional and interface clocks for the module.
    
    The clkctrl clocks are currently handled by arch/arm/mach-omap2 hwmod code.
    With this binding and a related clock device driver we can start moving the
    clkctrl clock handling to live in drivers/clk/ti.
    
    Note that this binding allows keeping the clockdomain related parts out of
    drivers/clock. The CLKCTCTRL and DYNAMICDEP registers can be handled by
    a separate driver in drivers/soc/ti and genpd. If the clockdomain driver
    needs to know it's clocks, we can just set the the clkctrl device
    instances to be children of the related clockdomain device.
    
    Each clkctrl clock can have multiple optional gate clocks, and multiple
    optional mux clocks. To represent this in device tree, it seems that
    it is best done using four clock cells #clock-cells = <2> property.
    
    The reasons for using #clock-cells = <2> are:
    
    1. We need to specify the clkctrl offset from the instance base. Otherwise
       we end up with a large number of device tree nodes that need to be
       patched when new clocks are discovered in a clkctrl clock with minor
       hardware revision changes for example
    
    2. On omap5 CM_L3INIT_USB_HOST_HS_CLKCTRL has ten OPTFCLKEN bits. So we
       need to use a separate cell for optional gate clocks to avoid address
       space conflicts
    
    There is probably no need to list input clocks for each clkctrl clock
    instance in the binding. If we want to add them, the standard clocks
    binding can be used for that.
    
    For hardware reference, see omap4430 TRM "Table 3-1312. L4PER_CM2 Registers
    Mapping Summary" for example. It shows one instance of a clkctrl clock
    controller with multiple clkctrl registers.
    
    Cc: Paul Walmsley <paul@pwsan.com>
    Acked-by: default avatarRob Herring <robh@kernel.org>
    Signed-off-by: default avatarTony Lindgren <tony@atomide.com>
    Signed-off-by: default avatarTero Kristo <t-kristo@ti.com>
    35395a9c
ti-clkctrl.txt 1.83 KB