• Alex Elder's avatar
    clk: bcm281xx: add initial clock framework support · 1f27f152
    Alex Elder authored
    Add code for device tree support of clocks in the BCM281xx family of
    SoCs.  Machines in this family use peripheral clocks implemented by
    "Kona" clock control units (CCUs).  (Other Broadcom SoC families use
    Kona style CCUs as well, but support for them is not yet upstream.)
    
    A BCM281xx SoC has multiple CCUs, each of which manages a set of
    clocks on the SoC.  A Kona peripheral clock is composite clock that
    may include a gate, a parent clock multiplexor, and zero, one
    or two dividers.  There is a variety of gate types, and many gates
    implement hardware-managed gating (often called "auto-gating").
    Most dividers divide their input clock signal by an integer value
    (one or more).  There are also "fractional" dividers which allow
    division by non-integer values.  To accomodate such dividers,
    clock rates and dividers are generally maintained by the code in
    "scaled" form, which allows integer and fractional dividers to
    be handled in a uniform way.
    
    If present, the gate for a Kona peripheral clock must be enabled
    when a change is made to its multiplexor or one of its dividers.
    Additionally, dividers and multiplexors have trigger registers which
    must be used whenever the divider value or selected parent clock is
    changed.  The same trigger is often used for a divider and
    multiplexor, and a BCM281xx peripheral clock occasionally has two
    triggers.
    
    The gate, dividers, and parent clock selector are treated in this
    code as "components" of a peripheral clock.  Their functionality is
    implemented directly--e.g. the common clock framework gate
    implementation is not used for a Kona peripheral clock gate.  (This
    has being considered though, and the intention is to evolve this
    code to leverage common code as much as possible.)
    
    The source code is divided into three general portions:
    
        drivers/clk/bcm/clk-kona.h
        drivers/clk/bcm/clk-kona.c
            These implement the basic Kona clock functionality,
            including the clk_ops methods and various routines to
            manipulate registers and interpret their values.  This
            includes some functions used to set clocks to a desired
            initial state (though this feature is only partially
            implemented here).
    
        drivers/clk/bcm/clk-kona-setup.c
            This contains generic run-time initialization code for
            data structures representing Kona CCUs and clocks.  This
            encapsulates the clock structure initialization that can't
            be done statically.  Note that there is a great deal of
            validity-checking code here, making explicit certain
            assumptions in the code.   This is mostly useful for adding
            new clock definitions and could possibly be disabled for
            production use.
    
        drivers/clk/bcm/clk-bcm281xx.c
            This file defines the specific CCUs used by BCM281XX family
            SoCs, as well as the specific clocks implemented by each.
            It declares a device tree clock match entry for each CCU
            defined.
    
        include/dt-bindings/clock/bcm281xx.h
            This file defines the selector (index) values used to
            identify a particular clock provided by a CCU.  It consists
            entirely of C preprocessor constants, to be used by both the
            C source and device tree source files.
    Signed-off-by: default avatarAlex Elder <elder@linaro.org>
    Reviewed-by: default avatarTim Kryger <tim.kryger@linaro.org>
    Reviewed-by: default avatarMatt Porter <mporter@linaro.org>
    Acked-by: default avatarMike Turquette <mturquette@linaro.org>
    Signed-off-by: default avatarMatt Porter <mporter@linaro.org>
    1f27f152
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