Re: [PATCH] clk: Add device tree binding to clk-fixed-factor

[Christian Ruppert]

Hi Gregory,

We use derived clocks with fixed ratios for our TB10x platform. I
originally had this in the platform code but Vineet (the platform
maintainer) rightly pointed out that the common clock framework would
be the correct place for it.
Is there any reason not to support this functionality? After all, the
generic fixed rate clock also has a device tree binding and I'd guess
we're not the only ones statically deriving one clock from another in
our SOCs.

Greetings,
  Christian

On Wed, Apr 10, 2013 at 05:56:25PM +0200, Gregory CLEMENT wrote:
> Hi Christian,
> 
> On 04/10/2013 05:40 PM, Christian Ruppert wrote:
> > This patch adds a device tree binding for the simple fixed factor clock
> > divider/multiplier of the common clock tree binding.
> 
> This patch remind me of something :
> http://lists.infradead.org/pipermail/linux-arm-kernel/2012-August/116405.html
> 
> Do you have a use case for it, this time?
> 
> My version have been hold off waiting for an user for it.
> Will you need it for a driver?
> 
> Regards,
> 
> > 
> > Signed-off-by: Christian Ruppert <christian.ruppert@xxxxxxxxxx>
> > ---
> >  .../bindings/clock/fixed-factor-clkdiv.txt         |   24 +++++++++++++++
> >  drivers/clk/clk-fixed-factor.c                     |   32 ++++++++++++++++++++
> >  include/linux/clk-provider.h                       |    1 +
> >  3 files changed, 57 insertions(+), 0 deletions(-)
> >  create mode 100644 Documentation/devicetree/bindings/clock/fixed-factor-clkdiv.txt
> > 
> > diff --git a/Documentation/devicetree/bindings/clock/fixed-factor-clkdiv.txt b/Documentation/devicetree/bindings/clock/fixed-factor-clkdiv.txt
> > new file mode 100644
> > index 0000000..352bac4
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/clock/fixed-factor-clkdiv.txt
> > @@ -0,0 +1,24 @@
> > +Device Tree Clock bindings for plat-tb10x
> > +
> > +This binding uses the common clock binding[1].
> > +
> > +[1] Documentation/devicetree/bindings/clock/clock-bindings.txt
> > +
> > +Required properties:
> > +- compatible : shall be "fixed-factor-clkdiv"
> > +- #clock-cells: from common clock binding; shall be set to 0
> > +- clocks: shall be the input parent clock phandle for the clock.
> > +- clock-mult: defines the multiplication factor of the output clock frequency
> > +  wrt. the input clock frequency.
> > +- clock-div: defines the division factor of the output clock frequency wrt.
> > +  the input clock frequency.
> > +
> > +Example:
> > +cpu_clk: clkdiv_cpu {	/* CPU clock derived from pll0. 1/2 of pll frequency */
> > +	compatible = "fixed-factor-clkdiv";
> > +	#clock-cells = <0>;
> > +	clocks = <&pll0>;
> > +	clock-mult = <1>;
> > +	clock-div = <2>;
> > +	clock-output-names = "cpu_clk";
> > +};
> > diff --git a/drivers/clk/clk-fixed-factor.c b/drivers/clk/clk-fixed-factor.c
> > index 1ef271e..85e45f1 100644
> > --- a/drivers/clk/clk-fixed-factor.c
> > +++ b/drivers/clk/clk-fixed-factor.c
> > @@ -11,6 +11,7 @@
> >  #include <linux/clk-provider.h>
> >  #include <linux/slab.h>
> >  #include <linux/err.h>
> > +#include <linux/of.h>
> >  
> >  /*
> >   * DOC: basic fixed multiplier and divider clock that cannot gate
> > @@ -96,3 +97,34 @@ struct clk *clk_register_fixed_factor(struct device *dev, const char *name,
> >  
> >  	return clk;
> >  }
> > +
> > +#ifdef CONFIG_OF
> > +/**
> > + * of_fixed_factor_clkdiv_setup() - Set up simple fixed factor clock divider
> > + */
> > +void of_fixed_factor_clkdiv_setup(struct device_node *node)
> > +{
> > +	struct clk *clk;
> > +	const char *clk_name = node->name;
> > +	const char *parent_name;
> > +	u32 mult, div;
> > +
> > +	if (of_property_read_u32(node, "clock-mult", &mult))
> > +		return;
> > +
> > +	if (of_property_read_u32(node, "clock-div", &div))
> > +		return;
> > +
> > +	parent_name = of_clk_get_parent_name(node, 0);
> > +
> > +	of_property_read_string(node, "clock-output-names", &clk_name);
> > +
> > +	clk = clk_register_fixed_factor(NULL, clk_name, parent_name, 0,
> > +					mult, div);
> > +	if (!IS_ERR(clk))
> > +		of_clk_add_provider(node, of_clk_src_simple_get, clk);
> > +}
> > +EXPORT_SYMBOL_GPL(of_fixed_factor_clkdiv_setup);
> > +CLK_OF_DECLARE(fixed_clkdiv, "fixed-factor-clkdiv",
> > +		of_fixed_factor_clkdiv_setup);
> > +#endif
> > diff --git a/include/linux/clk-provider.h b/include/linux/clk-provider.h
> > index 7f197d7..d4937cf 100644
> > --- a/include/linux/clk-provider.h
> > +++ b/include/linux/clk-provider.h
> > @@ -184,6 +184,7 @@ struct clk *clk_register_fixed_rate(struct device *dev, const char *name,
> >  		unsigned long fixed_rate);
> >  
> >  void of_fixed_clk_setup(struct device_node *np);
> > +void of_fixed_factor_clkdiv_setup(struct device_node *node);
> >  
> >  /**
> >   * struct clk_gate - gating clock
> > 
> 
> 
> -- 
> Gregory Clement, Free Electrons
> Kernel, drivers, real-time and embedded Linux
> development, consulting, training and support.
> http://free-electrons.com

-- 
  Christian Ruppert              ,          <christian.ruppert@xxxxxxxxxx>
                                /|
  Tel: +41/(0)22 816 19-42     //|                 3, Chemin du Pré-Fleuri
                             _// | bilis Systems   CH-1228 Plan-les-Ouates
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