Re: [PATCH] clk: add gpio gated clock

[Mike Turquette]

Quoting Jyri Sarha (2014-09-05 05:21:34)
> The added gpio-gate-clock is a basic clock that can be enabled and
> disabled trough a gpio output. The DT binding document for the clock
> is also added. For EPROBE_DEFER handling the registering of the clock
> has to be delayed until of_clk_get() call time.
> 
> Signed-off-by: Jyri Sarha <jsarha@xxxxxx>
> ---
> 
> This is my final attempt to get this generic gpio controlled basic
> clock into mainline. Of course I gladly fix any issues that the patch
> may have. However, if there is no response, I give up and move it to TI
> specific clocks.
> 

I searched through my archives and found a post from January. You Cc'd
me as "<mturquette@xxxxxxxxxx>". Note that the address is wrapped in
chevrons but there is no name string (e.g. "Mike Turquette").

My mailer doesn't parse this well it was not flagged as to:me in my
filters. Maybe other mailers handle this better? If you leave out the
name string in the future then it would probably be best to drop the
chevrons.

> I've been sending this patch as a part of Beaglebone-Black HDMI audio
> patch series since last autumn. Since the previous version I have done
> some minor cleanups and changed the clock's compatible property from
> "gpio-clock" to "gpio-gate-clock". All the file names, comments,
> etc. have also been changed accordingly.

Is your platform the only one to take advantage of this clock type so
far? I feel that it is esoteric enough that it shouldn't be made
generic.

The main reason is that all of the generic clock types needs to be
overhauled at some point. E.g. the clk-gate should have its
machine-specific logic separated from its machine-independent logic. If
the gate clock were to populate .enable and .disable callbacks and then
leave the actual register banging, or regmap'ing, or gpio'ing up to your
backend driver then that would be a big improvement and would avoid the
need to create this new clock type outright.

So that's on my todo list, but it's not done yet. For your patch I think
that putting this code into drivers/clk/ti would probably be best,
unless other folks could use it as-is. Even if others could use it today
I would want to remove it eventually for the reasons stated in the
paragraph above.

Regards,
Mike

> 
> Best regards,
> Jyri
> 
>  .../devicetree/bindings/clock/gpio-gate-clock.txt  |   21 ++
>  drivers/clk/Makefile                               |    1 +
>  drivers/clk/clk-gpio-gate.c                        |  204 ++++++++++++++++++++
>  include/linux/clk-provider.h                       |   22 +++
>  4 files changed, 248 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/clock/gpio-gate-clock.txt
>  create mode 100644 drivers/clk/clk-gpio-gate.c
> 
> diff --git a/Documentation/devicetree/bindings/clock/gpio-gate-clock.txt b/Documentation/devicetree/bindings/clock/gpio-gate-clock.txt
> new file mode 100644
> index 0000000..d3379ff
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/clock/gpio-gate-clock.txt
> @@ -0,0 +1,21 @@
> +Binding for simple gpio gated clock.
> +
> +This binding uses the common clock binding[1].
> +
> +[1] Documentation/devicetree/bindings/clock/clock-bindings.txt
> +
> +Required properties:
> +- compatible : shall be "gpio-gate-clock".
> +- #clock-cells : from common clock binding; shall be set to 0.
> +- enable-gpios : GPIO reference for enabling and disabling the clock.
> +
> +Optional properties:
> +- clocks: Maximum of one parent clock is supported.
> +
> +Example:
> +       clock {
> +               compatible = "gpio-gate-clock";
> +               clocks = <&parentclk>;
> +               #clock-cells = <0>;
> +               enable-gpios = <&gpio 1 GPIO_ACTIVE_HIGH>;
> +       };
> diff --git a/drivers/clk/Makefile b/drivers/clk/Makefile
> index f537a0b..5d78710 100644
> --- a/drivers/clk/Makefile
> +++ b/drivers/clk/Makefile
> @@ -9,6 +9,7 @@ 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-fractional-divider.o
> +obj-$(CONFIG_COMMON_CLK)       += clk-gpio-gate.o
>  ifeq ($(CONFIG_OF), y)
>  obj-$(CONFIG_COMMON_CLK)       += clk-conf.o
>  endif
> diff --git a/drivers/clk/clk-gpio-gate.c b/drivers/clk/clk-gpio-gate.c
> new file mode 100644
> index 0000000..9dde885
> --- /dev/null
> +++ b/drivers/clk/clk-gpio-gate.c
> @@ -0,0 +1,204 @@
> +/*
> + * Copyright (C) 2013 - 2014 Texas Instruments Incorporated - http://www.ti.com
> + * Author: Jyri Sarha <jsarha@xxxxxx>
> + *
> + * 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
> + * published by the Free Software Foundation.
> + *
> + * Gpio gated clock implementation
> + */
> +
> +#include <linux/clk-provider.h>
> +#include <linux/module.h>
> +#include <linux/slab.h>
> +#include <linux/gpio.h>
> +#include <linux/of_gpio.h>
> +#include <linux/err.h>
> +#include <linux/device.h>
> +
> +/**
> + * DOC: basic gpio gated clock which can be enabled and disabled
> + *      with gpio output
> + * Traits of this clock:
> + * prepare - clk_(un)prepare only ensures parent is (un)prepared
> + * enable - clk_enable and clk_disable are functional & control gpio
> + * rate - inherits rate from parent.  No clk_set_rate support
> + * parent - fixed parent.  No clk_set_parent support
> + */
> +
> +#define to_clk_gpio(_hw) container_of(_hw, struct clk_gpio, hw)
> +
> +static int clk_gpio_gate_enable(struct clk_hw *hw)
> +{
> +       struct clk_gpio *clk = to_clk_gpio(hw);
> +
> +       gpiod_set_value(clk->gpiod, 1);
> +
> +       return 0;
> +}
> +
> +static void clk_gpio_gate_disable(struct clk_hw *hw)
> +{
> +       struct clk_gpio *clk = to_clk_gpio(hw);
> +
> +       gpiod_set_value(clk->gpiod, 0);
> +}
> +
> +static int clk_gpio_gate_is_enabled(struct clk_hw *hw)
> +{
> +       struct clk_gpio *clk = to_clk_gpio(hw);
> +
> +       return gpiod_get_value(clk->gpiod);
> +}
> +
> +const struct clk_ops clk_gpio_gate_ops = {
> +       .enable = clk_gpio_gate_enable,
> +       .disable = clk_gpio_gate_disable,
> +       .is_enabled = clk_gpio_gate_is_enabled,
> +};
> +EXPORT_SYMBOL_GPL(clk_gpio_gate_ops);
> +
> +/**
> + * clk_register_gpio - register a gpip clock with the clock framework
> + * @dev: device that is registering this clock
> + * @name: name of this clock
> + * @parent_name: name of this clock's parent
> + * @gpiod: gpio descriptor to gate this clock
> + */
> +struct clk *clk_register_gpio_gate(struct device *dev, const char *name,
> +               const char *parent_name, struct gpio_desc *gpiod,
> +               unsigned long flags)
> +{
> +       struct clk_gpio *clk_gpio = NULL;
> +       struct clk *clk = ERR_PTR(-EINVAL);
> +       struct clk_init_data init = { NULL };
> +       unsigned long gpio_flags;
> +       int err;
> +
> +       if (gpiod_is_active_low(gpiod))
> +               gpio_flags = GPIOF_OUT_INIT_HIGH;
> +       else
> +               gpio_flags = GPIOF_OUT_INIT_LOW;
> +
> +       if (dev)
> +               err = devm_gpio_request_one(dev, desc_to_gpio(gpiod),
> +                                           gpio_flags, name);
> +       else
> +               err = gpio_request_one(desc_to_gpio(gpiod), gpio_flags, name);
> +
> +       if (err) {
> +               pr_err("%s: %s: Error requesting clock control gpio %u\n",
> +                      __func__, name, desc_to_gpio(gpiod));
> +               return ERR_PTR(err);
> +       }
> +
> +       if (dev)
> +               clk_gpio = devm_kzalloc(dev, sizeof(struct clk_gpio),
> +                                       GFP_KERNEL);
> +       else
> +               clk_gpio = kzalloc(sizeof(struct clk_gpio), GFP_KERNEL);
> +
> +       if (!clk_gpio) {
> +               clk = ERR_PTR(-ENOMEM);
> +               goto clk_register_gpio_gate_err;
> +       }
> +
> +       init.name = name;
> +       init.ops = &clk_gpio_gate_ops;
> +       init.flags = flags | CLK_IS_BASIC;
> +       init.parent_names = (parent_name ? &parent_name : NULL);
> +       init.num_parents = (parent_name ? 1 : 0);
> +
> +       clk_gpio->gpiod = gpiod;
> +       clk_gpio->hw.init = &init;
> +
> +       clk = clk_register(dev, &clk_gpio->hw);
> +
> +       if (!IS_ERR(clk))
> +               return clk;
> +
> +       if (!dev)
> +               kfree(clk_gpio);
> +
> +clk_register_gpio_gate_err:
> +       gpiod_put(gpiod);
> +
> +       return clk;
> +}
> +EXPORT_SYMBOL_GPL(clk_register_gpio_gate);
> +
> +#ifdef CONFIG_OF
> +/**
> + * The clk_register_gpio_gate has to be delayed, because the EPROBE_DEFER
> + * can not be handled properly at of_clk_init() call time.
> + */
> +
> +struct clk_gpio_gate_delayed_register_data {
> +       struct device_node *node;
> +       struct mutex lock;
> +       struct clk *clk;
> +};
> +
> +static struct clk *of_clk_gpio_gate_delayed_register_get(
> +               struct of_phandle_args *clkspec,
> +               void *_data)
> +{
> +       struct clk_gpio_gate_delayed_register_data *data = _data;
> +       struct clk *clk;
> +       const char *clk_name = data->node->name;
> +       const char *parent_name;
> +       struct gpio_desc *gpiod;
> +       int gpio;
> +
> +       mutex_lock(&data->lock);
> +
> +       if (data->clk) {
> +               mutex_unlock(&data->lock);
> +               return data->clk;
> +       }
> +
> +       gpio = of_get_named_gpio_flags(data->node, "enable-gpios", 0, NULL);
> +       if (gpio < 0) {
> +               mutex_unlock(&data->lock);
> +               if (gpio != -EPROBE_DEFER)
> +                       pr_err("%s: %s: Can't get 'enable-gpios' DT property\n",
> +                              __func__, clk_name);
> +               return ERR_PTR(gpio);
> +       }
> +       gpiod = gpio_to_desc(gpio);
> +
> +       parent_name = of_clk_get_parent_name(data->node, 0);
> +
> +       clk = clk_register_gpio_gate(NULL, clk_name, parent_name, gpiod, 0);
> +       if (IS_ERR(clk)) {
> +               mutex_unlock(&data->lock);
> +               return clk;
> +       }
> +
> +       data->clk = clk;
> +       mutex_unlock(&data->lock);
> +
> +       return clk;
> +}
> +
> +/**
> + * of_gpio_gate_clk_setup() - Setup function for gpio controlled clock
> + */
> +void __init of_gpio_gate_clk_setup(struct device_node *node)
> +{
> +       struct clk_gpio_gate_delayed_register_data *data;
> +
> +       data = kzalloc(sizeof(struct clk_gpio_gate_delayed_register_data),
> +                      GFP_KERNEL);
> +       if (!data)
> +               return;
> +
> +       data->node = node;
> +       mutex_init(&data->lock);
> +
> +       of_clk_add_provider(node, of_clk_gpio_gate_delayed_register_get, data);
> +}
> +EXPORT_SYMBOL_GPL(of_gpio_gate_clk_setup);
> +CLK_OF_DECLARE(gpio_gate_clk, "gpio-gate-clock", of_gpio_gate_clk_setup);
> +#endif
> diff --git a/include/linux/clk-provider.h b/include/linux/clk-provider.h
> index 411dd7e..ec1581b 100644
> --- a/include/linux/clk-provider.h
> +++ b/include/linux/clk-provider.h
> @@ -488,6 +488,28 @@ struct clk *clk_register_composite(struct device *dev, const char *name,
>                 struct clk_hw *gate_hw, const struct clk_ops *gate_ops,
>                 unsigned long flags);
>  
> +/***
> + * struct clk_gpio_gate - gpio gated clock
> + *
> + * @hw:                handle between common and hardware-specific interfaces
> + * @gpiod:     gpio descriptor
> + *
> + * Clock with a gpio control for enabling and disabling the parent clock.
> + * Implements .enable, .disable and .is_enabled
> + */
> +
> +struct clk_gpio {
> +       struct clk_hw   hw;
> +       struct gpio_desc *gpiod;
> +};
> +
> +extern const struct clk_ops clk_gpio_gate_ops;
> +struct clk *clk_register_gpio_gate(struct device *dev, const char *name,
> +               const char *parent_name, struct gpio_desc *gpio,
> +               unsigned long flags);
> +
> +void of_gpio_clk_gate_setup(struct device_node *node);
> +
>  /**
>   * clk_register - allocate a new clock, register it and return an opaque cookie
>   * @dev: device that is registering this clock
> -- 
> 1.7.9.5
> 
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