Message-Id: <2A930389-012E-45C3-93EB-6B4A41DB2EF5@codeaurora.org>
Date:	Wed, 28 Aug 2013 10:50:10 -0500
From:	Kumar Gala <galak@...eaurora.org>
To:	Mike Turquette <mturquette@...aro.org>
Cc:	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	Matt Sealey <neko@...uhatsu.net>,
	Stephen Boyd <sboyd@...eaurora.org>,
	Haojian Zhuang <haojian.zhuang@...aro.org>,
	Tero Kristo <t-kristo@...com>,
	Heiko Stübner <heiko@...ech.de>,
	devicetree@...r.kernel.org
Subject: Re: [PATCH v4 3/5] clk: dt: binding for basic multiplexer clock


On Aug 22, 2013, at 12:53 AM, 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 <mturquette@...aro.org>
> Tested-by: Heiko Stuebner <heiko@...ech.de>
> Reviewed-by: Heiko Stuebner <heiko@...ech.de>
> ---
> Changes since v3:
> * replaced underscores with dashes in DT property names
> * bail from of clock setup function early if of_iomap fails
> * removed unecessary explict cast
> 
> .../devicetree/bindings/clock/mux-clock.txt        | 79 ++++++++++++++++++++++
> drivers/clk/clk-mux.c                              | 68 ++++++++++++++++++-
> include/linux/clk-provider.h                       |  5 +-
> 3 files changed, 150 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..21eb3b3
> --- /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-starts-at-one" modified the scheme as follows:
> +
> +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>;
> +

I think this is going way too far for what should be in a device tree.  Why should this not just be encoded in tables in the code?

> +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@...08100 {
> +		compatible = "mux-clock";
> +		#clock-cells = <0>;
> +		clocks = <&clock_foo>, <&clock_bar>, <&clock_baz>;
> +		reg = <0x4a008100 0x4>
> +		mask = <0x3>;
> +		index-starts-at-one;
> +	};
> +
> +	clock: clock@...08100 {
> +		#clock-cells = <0>;
> +		compatible = "mux-clock";
> +		clocks = <&clock_foo>, <&clock_bar>, <&clock_baz>;
> +		reg = <0x4a008100 0x4>;
> +		mask = <0x3>;
> +		shift = <0>;
> +		table = <&clock_foo 1>, <&clock_bar 2>, <&clock_baz 3>;
> +	};
> diff --git a/drivers/clk/clk-mux.c b/drivers/clk/clk-mux.c
> index 0811633..9292253 100644
> --- a/drivers/clk/clk-mux.c
> +++ b/drivers/clk/clk-mux.c
> @@ -1,7 +1,7 @@
> /*
>  * Copyright (C) 2011 Sascha Hauer, Pengutronix <s.hauer@...gutronix.de>
>  * Copyright (C) 2011 Richard Zhao, Linaro <richard.zhao@...aro.org>
> - * Copyright (C) 2011-2012 Mike Turquette, Linaro Ltd <mturquette@...aro.org>
> + * Copyright (C) 2011-2013 Mike Turquette, Linaro Ltd <mturquette@...aro.org>
>  *
>  * This program is free software; you can redistribute it and/or modify
>  * it under the terms of the GNU General Public License version 2 as
> @@ -16,6 +16,8 @@
> #include <linux/slab.h>
> #include <linux/io.h>
> #include <linux/err.h>
> +#include <linux/of.h>
> +#include <linux/of_address.h>
> 
> /*
>  * DOC: basic adjustable multiplexer clock that cannot gate
> @@ -177,3 +179,67 @@ struct clk *clk_register_mux(struct device *dev, const char *name,
> 				      NULL, lock);
> }
> EXPORT_SYMBOL_GPL(clk_register_mux);
> +
> +#ifdef CONFIG_OF
> +/**
> + * 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);
> +	if (!reg) {
> +		pr_err("%s: no memory mapped for property reg\n", __func__);
> +		return;
> +	}
> +
> +	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, shift, mask, clk_mux_flags, NULL, NULL);
> +
> +	if (!IS_ERR(clk))
> +		of_clk_add_provider(node, of_clk_src_simple_get, clk);
> +}
> +EXPORT_SYMBOL_GPL(of_mux_clk_setup);
> +CLK_OF_DECLARE(mux_clk, "mux-clock", of_mux_clk_setup);
> +#endif
> diff --git a/include/linux/clk-provider.h b/include/linux/clk-provider.h
> index 5497739..e019212 100644
> --- a/include/linux/clk-provider.h
> +++ b/include/linux/clk-provider.h
> @@ -350,7 +350,7 @@ struct clk *clk_register_mux_table(struct device *dev, const char *name,
> 		void __iomem *reg, u8 shift, u32 mask,
> 		u8 clk_mux_flags, u32 *table, spinlock_t *lock);
> 
> -void of_fixed_factor_clk_setup(struct device_node *node);
> +void of_mux_clk_setup(struct device_node *node);
> 
> /**
>  * struct clk_fixed_factor - fixed multiplier and divider clock
> @@ -371,10 +371,13 @@ struct clk_fixed_factor {
> };
> 
> extern struct clk_ops clk_fixed_factor_ops;
> +
> struct clk *clk_register_fixed_factor(struct device *dev, const char *name,
> 		const char *parent_name, unsigned long flags,
> 		unsigned int mult, unsigned int div);
> 
> +void of_fixed_factor_clk_setup(struct device_node *node);
> +
> /***
>  * struct clk_composite - aggregate clock of mux, divider and gate clocks
>  *
> -- 
> 1.8.1.2
> 
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