Subject: [PATCH v3 3/5] clk: dt: binding for basic multiplexer clock

From: [email-masked] (Mike Turquette)
Date: Tue, 09 Jul 2013 06:58:08 -0700

Quoting Mark Rutland (2013-06-26 01:40:58)
> Hi,
> 
> I have a couple of minor comments.
> 
> On Fri, Jun 21, 2013 at 07:14:14AM +0100, Mike Turquette wrote:
> > Device Tree binding for the basic clock multiplexer, plus the setup
> > function to register the clock.  Based on the existing fixed-clock
> > binding.
> > 
> > Includes minor beautification of clk-provider.h where some whitespace is
> > added and of_fixed_factor_clock_setup is relocated to maintain a
> > consistent style.
> > 
> > Tero Kristo contributed helpful bug fixes to this patch.
> > 
> > Signed-off-by: Mike Turquette <[email-masked]>
> > ---
> > Changes since v2:
> > * added hiword-mask property to the binding
> > * changed bit-shift property from u8 to u32 in the dt binding
> > 
> > Changes since v1:
> > * pass shift value into clk_register_mux_table
> > * s/multiplexor/multiplexer/
> > * removed debug prints
> > * mask is u32, shift is u8
> > * DT property names use dashes instead of underscores
> > * DT property names are more verbose
> > * shift property is optional in binding and can be auto-generated from a
> >   full 32-bit mask
> > 
> >  .../devicetree/bindings/clock/mux-clock.txt        | 79 ++++++++++++++++++++++
> >  drivers/clk/clk-mux.c                              | 65 +++++++++++++++++-
> >  include/linux/clk-provider.h                       |  5 +-
> >  3 files changed, 147 insertions(+), 2 deletions(-)
> >  create mode 100644 Documentation/devicetree/bindings/clock/mux-clock.txt
> > 
> > diff --git a/Documentation/devicetree/bindings/clock/mux-clock.txt b/Documentation/devicetree/bindings/clock/mux-clock.txt
> > new file mode 100644
> > index 0000000..54cb8d1
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/clock/mux-clock.txt
> > @@ -0,0 +1,79 @@
> > +Binding for simple mux clock.
> > +
> > +This binding uses the common clock binding[1].  It assumes a
> > +register-mapped multiplexer with multiple input clock signals or
> > +parents, one of which can be selected as output.  This clock does not
> > +gate or adjust the parent rate via a divider or multiplier.
> > +
> > +By default the "clocks" property lists the parents in the same order
> > +as they are programmed into the regster.  E.g:
> > +
> > +     clocks = <&foo_clock>, <&bar_clock>, <&baz_clock>;
> > +
> > +results in programming the register as follows:
> > +
> > +register value               selected parent clock
> > +0                    foo_clock
> > +1                    bar_clock
> > +2                    baz_clock
> > +
> > +Some clock controller IPs do not allow a value of zero to be programmed
> > +into the register, instead indexing begins at 1.  The optional property
> > +"index_one" modified the scheme as follows:
> 
> I assume this is meant to be "index-starts-at-one", given the code and
> changelog?
> 
> > +
> > +register value               selected clock parent
> > +1                    foo_clock
> > +2                    bar_clock
> > +3                    baz_clock
> > +
> > +Additionally an optional table of bit and parent pairs may be supplied
> > +like so:
> > +
> > +     table = <&foo_clock 0x0>, <&bar_clock, 0x2>, <&baz_clock, 0x4>;
> > +
> > +where the first value in the pair is the parent clock and the second
> > +value is the bitfield to be programmed into the register.
> > +
> > +The binding must provide the register to control the mux and the mask
> > +for the corresponding control bits.  Optionally the number of bits to
> > +shift that mask if necessary.  If the shift value is missing it is the
> > +same as supplying a zero shift.
> > +
> > +[1] Documentation/devicetree/bindings/clock/clock-bindings.txt
> > +
> > +Required properties:
> > +- compatible : shall be "mux-clock".
> > +- #clock-cells : from common clock binding; shall be set to 0.
> > +- clocks : link phandles of parent clocks
> > +- reg : base address for register controlling adjustable mux
> > +- bit-mask : arbitrary bitmask for programming the adjustable mux
> > +
> > +Optional properties:
> > +- clock-output-names : From common clock binding.
> > +- table : array of integer pairs defining parents & bitfield values
> > +- bit-shift : number of bits to shift the bit-mask, defaults to
> > +  (ffs(mask) - 1) if not present
> > +- index-starts-at-one : valid input select programming starts at 1, not
> > +  zero
> > +- hiword-mask : lower half of the register programs the mux, upper half
> > +  of the register indicates bits that were updated in the lower half
> > +
> > +Examples:
> > +     clock: clock at 4a008100 {
> > +             compatible = "mux-clock";
> > +             #clock-cells = <0>;
> > +             clocks = <&clock_foo>, <&clock_bar>, <&clock_baz>;
> > +             reg = <0x4a008100 0x4>
> > +             mask = <0x3>;
> > +             index_one;
> 
> And here too?
> 
> [...]
> 
> > +/**
> > + * of_mux_clk_setup() - Setup function for simple mux rate clock
> > + */
> > +void of_mux_clk_setup(struct device_node *node)
> > +{
> > +     struct clk *clk;
> > +     const char *clk_name = node->name;
> > +     void __iomem *reg;
> > +     int num_parents;
> > +     const char **parent_names;
> > +     int i;
> > +     u8 clk_mux_flags = 0;
> > +     u32 mask = 0;
> > +     u32 shift = 0;
> > +
> > +     of_property_read_string(node, "clock-output-names", &clk_name);
> > +
> > +     num_parents = of_clk_get_parent_count(node);
> > +     if (num_parents < 1) {
> > +             pr_err("%s: mux-clock %s must have parent(s)\n",
> > +                             __func__, node->name);
> > +             return;
> > +     }
> > +
> > +     parent_names = kzalloc((sizeof(char*) * num_parents),
> > +                     GFP_KERNEL);
> > +
> > +     for (i = 0; i < num_parents; i++)
> > +             parent_names[i] = of_clk_get_parent_name(node, i);
> > +
> > +     reg = of_iomap(node, 0);
> 
> Would it not be a good idea to check this isn't NULL before we pass it
> to clk_register_mux_table later?
> 
> > +
> > +     if (of_property_read_u32(node, "bit-mask", &mask)) {
> > +             pr_err("%s: missing bit-mask property for %s\n", __func__, node->name);
> > +             return;
> > +     }
> > +
> > +     if (of_property_read_u32(node, "bit-shift", &shift)) {
> > +             shift = __ffs(mask);
> > +             pr_debug("%s: bit-shift property defaults to 0x%x for %s\n",
> > +                             __func__, shift, node->name);
> > +     }
> > +
> > +     if (of_property_read_bool(node, "index-starts-at-one"))
> > +             clk_mux_flags |= CLK_MUX_INDEX_ONE;
> > +
> > +     if (of_property_read_bool(node, "hiword-mask"))
> > +             clk_mux_flags |= CLK_MUX_HIWORD_MASK;
> > +
> > +     clk = clk_register_mux_table(NULL, clk_name, parent_names, num_parents,
> > +                     0, reg, (u8) shift, mask, clk_mux_flags,
> > +                     NULL, NULL);
> 
> Why do you need the (u8) cast on shift? Isn't that implicit?

All of your suggestions are good. I'll roll them into the next version.

Regards,
Mike
> Thanks,
> Mark.