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Message-ID: <20130529173938.6058.96646@quantum>
Date: Wed, 29 May 2013 10:39:38 -0700
From: Mike Turquette <mturquette@...aro.org>
To: James Hogan <james.hogan@...tec.com>,
<linux-arm-kernel@...ts.infradead.org>
Cc: <devicetree-discuss@...ts.ozlabs.org>, <linux-doc@...r.kernel.org>,
<linux-kernel@...r.kernel.org>,
James Hogan <james.hogan@...tec.com>,
"Grant Likely" <grant.likely@...retlab.ca>,
Rob Herring <rob.herring@...xeda.com>,
Rob Landley <rob@...dley.net>, Arnd Bergmann <arnd@...db.de>,
Linus Walleij <linus.walleij@...aro.org>,
Mark Brown <broonie@...nsource.wolfsonmicro.com>,
Lars-Peter Clausen <lars@...afoo.de>
Subject: Re: [PATCH] clk: add specified-rate clock
Quoting James Hogan (2013-05-10 05:44:22)
> The frequency of some SoC's external oscillators (for example TZ1090's
> XTAL1) are configured by the board using pull-ups/pull-downs of
> configuration pins, the logic values of which are automatically latched
> on reset and available in an SoC register. Add a generic clock component
> and DT bindings to handle this.
>
> It behaves similar to a fixed rate clock (read-only), except it needs
> information about a register field (reg, shift, width), and the
> clock-frequency is a mapping from register field values to clock
> frequencies.
>
James,
Thanks for sending this! It looks mostly good and is a useful clock
type to support. Comments below.
<snip>
> diff --git a/Documentation/devicetree/bindings/clock/specified-clock.txt b/Documentation/devicetree/bindings/clock/specified-clock.txt
> new file mode 100644
> index 0000000..b36ccf9
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/clock/specified-clock.txt
> @@ -0,0 +1,39 @@
> +Binding for fixed-rate clock sources with readable configuration.
> +
> +This binding uses the common clock binding[1].
> +
> +[1] Documentation/devicetree/bindings/clock/clock-bindings.txt
> +
> +Required properties:
> +- compatible : Shall be "specified-clock".
> +- #clock-cells : From common clock binding; shall be set to 0.
> +- reg : Address of configuration register.
> +- shift : Shift of config value field in configuration register.
> +- width : Width of config value field in configuration register.
It might be better to make this a mask instead of the width. We have
already hit this issue with the mux table on Nvidia where arbitrary
masks are necessary. Mask + shift probably helps future-proof us a bit.
The rest of the binding looks good.
<snip>
> diff --git a/drivers/clk/Makefile b/drivers/clk/Makefile
> index e7f7fe9..1343179 100644
> --- a/drivers/clk/Makefile
> +++ b/drivers/clk/Makefile
> @@ -8,6 +8,7 @@ obj-$(CONFIG_COMMON_CLK) += clk-fixed-rate.o
> obj-$(CONFIG_COMMON_CLK) += clk-gate.o
> obj-$(CONFIG_COMMON_CLK) += clk-mux.o
> obj-$(CONFIG_COMMON_CLK) += clk-composite.o
> +obj-$(CONFIG_COMMON_CLK) += clk-specified-rate.o
One thing that does occur to me is that this could potentially be
combined with the fixed-rate clock. If the properties for a specified
rate existing in the DT data then this code applies, otherwise the
existing fixed-rate code is used. I don't have a strong opinion about
combining the code, but something to consider.
<snip>
> +#ifdef CONFIG_OF
> +/**
> + * of_specified_clk_setup() - Setup function for specified fixed rate clock
> + */
> +void __init of_specified_clk_setup(struct device_node *node)
> +{
> + struct clk *clk;
> + const char *clk_name = node->name;
> + u32 shift, width, rate;
> + void __iomem *reg;
> + int len, num_rates, i;
> + struct property *prop;
> + struct clk_specified_rate_entry *rates;
> + const __be32 *p;
> +
> + of_property_read_string(node, "clock-output-names", &clk_name);
> +
> + if (of_property_read_u32(node, "shift", &shift)) {
> + pr_err("%s(%s): could not read shift property\n",
> + __func__, clk_name);
> + return;
> + }
> +
> + if (of_property_read_u32(node, "width", &width)) {
> + pr_err("%s(%s): could not read width property\n",
> + __func__, clk_name);
> + return;
> + }
> +
> + reg = of_iomap(node, 0);
> + if (!reg) {
> + pr_err("%s(%s): of_iomap failed\n",
> + __func__, clk_name);
> + return;
> + }
> +
> + /* check clock-frequency exists */
> + prop = of_find_property(node, "clock-frequency", &len);
> + if (!prop) {
> + pr_err("%s(%s): could not find clock-frequency property\n",
> + __func__, clk_name);
> + goto err_iounmap;
> + }
> +
> + if (len & (sizeof(u32)*2 - 1)) {
> + pr_err("%s(%s): clock-frequency has invalid size of %d bytes\n",
> + __func__, clk_name, len);
> + goto err_iounmap;
> + }
> + num_rates = len / (sizeof(*rates)*2);
This tripped me up for a few minutes. I think it is a bit weird to
count bytes as a way to validate length and determine the number of
pairs.
I have written a binding for mux clocks which can have a table of
parents and the code below shows how I parsed the table:
+ u32 pair[2];
+
+ table_size = of_count_phandle_with_args(node, "table", "#clock-cells");
+
+ if (table_size < 1)
+ return NULL;
+
+ table = kzalloc(sizeof(struct clk_div_table) * table_size, GFP_KERNEL);
+ if (!table) {
+ pr_err("%s: unable to allocate memory for %s table\n", __func__, node->name);
+ return NULL;
+ }
+
+ for (i = 0; i < table_size; i++) {
+ if (!of_property_read_u32_array(node, "table", pair, ARRAY_SIZE(pair))) {
+ table[i].val = pair[0];
+ table[i].div = pair[1];
+ }
+ }
I'll be posting the mux-clock binding soon :-)
Regards,
Mike
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