Subject: [RFC 1/2] pwrseq: Add subsystem to handle complex power sequences

From: [email-masked] (Hans de Goede)
Date: Thu, 19 Jun 2014 16:03:54 +0200

Hi,

Overall I like the idea, I've some comments on the implementation inline.

On 06/19/2014 03:04 PM, Ulf Hansson wrote:
> The pwrseq subsystem handles complex power sequences, typically useful
> for subsystems that makes use of discoverable buses, like for example
> MMC and I2C.

I2C is not discoverable, I do agree that this could be useful for spi and
i2c too, so you may want to reword things so that it does not look like
you're suggesting that i2c is discoverable.

> 
> The pwrseq subsystem is dependant on CONFIG_OF to be able to parse a DT
> childnode to find out what power sequence method to bind for a device.
> 
> From the DT childnode, the pwrseq DT parser tries to locate a
> "power-method" property, which string is matched towards the list of
> supported pwrseq methods.
> 
> Each pwrseq method implements it's own power sequence and interfaces
> the pwrseq core through a few callback functions.
> 
> To instantiate a pwrseq method, clients shall use the devm_pwrseq_get()
> API. If needed, clients can explicity drop the references to a pwrseq
> method using devm_pwrseq_put() API.
> 
> Besides instantiation, the pwrseq API provides clients opportunity to
> select a certain power state. In this intial version, PWRSEQ_POWER_ON
> and PWRSEQ_POWER_OFF are supported. Those are also mandatory for each
> pwrseq method to support.
> 
> Signed-off-by: Ulf Hansson <[email-masked]>
> ---
>  .../devicetree/bindings/pwrseq/pwrseq.txt          |   48 ++++++
>  drivers/Makefile                                   |    2 +-
>  drivers/pwrseq/Makefile                            |    2 +
>  drivers/pwrseq/core.c                              |  175 ++++++++++++++++++++
>  drivers/pwrseq/core.h                              |   37 +++++
>  drivers/pwrseq/method.c                            |   38 +++++
>  include/linux/pwrseq.h                             |   50 ++++++
>  7 files changed, 351 insertions(+), 1 deletion(-)
>  create mode 100644 Documentation/devicetree/bindings/pwrseq/pwrseq.txt
>  create mode 100644 drivers/pwrseq/Makefile
>  create mode 100644 drivers/pwrseq/core.c
>  create mode 100644 drivers/pwrseq/core.h
>  create mode 100644 drivers/pwrseq/method.c
>  create mode 100644 include/linux/pwrseq.h
> 
> diff --git a/Documentation/devicetree/bindings/pwrseq/pwrseq.txt b/Documentation/devicetree/bindings/pwrseq/pwrseq.txt
> new file mode 100644
> index 0000000..80848ae
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/pwrseq/pwrseq.txt
> @@ -0,0 +1,48 @@
> +Power sequence DT bindings
> +
> +Each power sequence method has a corresponding "power-method" property string.
> +This property shall be set in a subnode for a device. That subnode should also
> +describe resourses which are specific to that power method.
> +
> +Do note, power sequences as such isn't encoded through DT. Instead those are
> +implemented by each power method.
> +
> +Required subnode properties:
> +- power-method: should contain the string for the power method to bind.
> +
> +	Supported power methods: None.
> +
> +Example:
> +
> +Note, the "clock" power method in this example isn't actually supported, but
> +used to visualize how a childnode could be described.
> +
> +// WLAN SDIO channel
> +sdi1_per2 at 80118000 {
> +	compatible = "arm,pl18x", "arm,primecell";
> +	reg = <0x80118000 0x1000>;
> +	interrupts = <0 50 IRQ_TYPE_LEVEL_HIGH>;
> +
> +	dmas = <&dma 32 0 0x2>, /* Logical - DevToMem */
> +	       <&dma 32 0 0x0>; /* Logical - MemToDev */
> +	dma-names = "rx", "tx";
> +
> +	clocks = <&prcc_kclk 2 4>, <&prcc_pclk 2 6>;
> +	clock-names = "sdi", "apb_pclk";
> +
> +	arm,primecell-periphid = <0x10480180>;
> +	max-frequency = <100000000>;
> +	bus-width = <4>;
> +	non-removable;
> +	pinctrl-names = "default", "sleep";
> +	pinctrl-0 = <&sdi1_default_mode>;
> +	pinctrl-1 = <&sdi1_sleep_mode>;
> +
> +	status = "okay";
> +
> +	pwrseq: pwrseq1 {
> +		power-method = "clock";
> +		clocks = <&someclk 1 2>, <&someclk 3 4>;
> +		clock-names = "pwrseq1", "pwrseq2";
> +	};
> +};
> diff --git a/drivers/Makefile b/drivers/Makefile
> index f98b50d..ac1bf5b 100644
> --- a/drivers/Makefile
> +++ b/drivers/Makefile
> @@ -128,7 +128,7 @@ endif
>  obj-$(CONFIG_DCA)		+= dca/
>  obj-$(CONFIG_HID)		+= hid/
>  obj-$(CONFIG_PPC_PS3)		+= ps3/
> -obj-$(CONFIG_OF)		+= of/
> +obj-$(CONFIG_OF)		+= of/ pwrseq/
>  obj-$(CONFIG_SSB)		+= ssb/
>  obj-$(CONFIG_BCMA)		+= bcma/
>  obj-$(CONFIG_VHOST_RING)	+= vhost/
> diff --git a/drivers/pwrseq/Makefile b/drivers/pwrseq/Makefile
> new file mode 100644
> index 0000000..afb914f
> --- /dev/null
> +++ b/drivers/pwrseq/Makefile
> @@ -0,0 +1,2 @@
> +#Support for the power sequence subsystem
> +obj-y = core.o method.o
> diff --git a/drivers/pwrseq/core.c b/drivers/pwrseq/core.c
> new file mode 100644
> index 0000000..baf7bb6
> --- /dev/null
> +++ b/drivers/pwrseq/core.c
> @@ -0,0 +1,175 @@
> +/*
> + * Core of the power sequence subsystem
> + *
> + * Copyright (C) 2014 Linaro Ltd
> + *
> + * Author: Ulf Hansson <[email-masked]>
> + *
> + * License terms: GNU General Public License (GPL) version 2
> + */
> +
> +#include <linux/kernel.h>
> +#include <linux/export.h>
> +#include <linux/device.h>
> +#include <linux/string.h>
> +#include <linux/err.h>
> +#include <linux/of.h>
> +
> +#include <linux/pwrseq.h>
> +#include "core.h"
> +
> +static int pwrseq_find(const char *power_method)
> +{
> +	int i;
> +
> +	for (i = 0; pwrseq_methods[i].bind_method != NULL; i++)
> +		if (!strcasecmp(power_method, pwrseq_methods[i].method))
> +			return i;
> +	return -ENODEV;
> +}
> +
> +static void devm_pwrseq_release(struct device *dev, void *res)
> +{
> +	struct pwrseq *ps = res;
> +
> +	dev_dbg(dev, "%s: Release method=%s\n", __func__, ps->method);
> +
> +	ps->ps_ops->release(ps);
> +	of_node_put(ps->np_child);
> +}
> +
> +static struct pwrseq *pwrseq_get(struct device *dev,
> +				struct device_node *np,
> +				const char *power_method)
> +{
> +	struct pwrseq *ps;
> +	int ret;
> +
> +	ret = pwrseq_find(power_method);
> +	if (ret < 0)
> +		return ERR_PTR(ret);
> +
> +	ps = devres_alloc(devm_pwrseq_release, sizeof(ps), GFP_KERNEL);
> +	if (!ps)
> +		return ERR_PTR(-ENOMEM);

Why not have the method have a create or init function rather then a
bind function, passing in struct device_node *np to this function,
and let it have a struct containing what ever info it needs like this:

struct pwrseq_method_foo {
	struct pwrseq ps;
	/* more members */
};

And then have it alloc that struct and end with:

	return &pwrseq_method_foo->ps;

That way we only have one alloc rather then 2, and if we ever need to add
refcounting only one struct to refcount.

Also I'm not sold on how you're making this a devm only thing, and
are using devres_alloc to not only allocate memory for resource tracking,
but also the actual backing struct, that is not how devres_alloc is
intended to be used AFAIK.

A problem with having this one always devm managed is that it makes it
hard to use in library functions without side effects.

e.g. if you look at how your using this in mmc_of_parse in the next
patch, this gives mmc_of_parse the side-effect of having allocated
and bound the power-seq method, even if mmc_of_parse later
fails on e.g. gpio binding. If then for some reason the mmc host
probe method decides to not propagate the mmc_of_parse method
error (leading to freeing of all devm managed resources), then this is
undesirable.

Where as with a non devm version, it would be clear that on error
mmc_of_parse would need to explicitly release the pwrseq again.

I realize that pwrseq implementations likely will want to use
devm functions too, and I'm a great fan of devm. But this is something
to keep in mind. At a minimum the description of of_mmc_parse needs
to get updated with info about it having potential side-effects even
when it fails, and that failure should always be treated as a fatal
error and cause the host probe method to fail.

Regards,

Hans

> +
> +	ps->dev = dev;
> +	ps->np_child = np;
> +	ps->method = pwrseq_methods[ret].method;
> +
> +	/*
> +	 * The on/off states is mandatory to be supported. Additional states
> +	 * shall be added by each method during binding.
> +	 */
> +	ps->supported_states = PWRSEQ_POWER_OFF | PWRSEQ_POWER_ON;
> +	/*
> +	 * The default current state is PWRSEQ_POWER_OFF, it may be updated
> +	 * during binding.
> +	 */
> +	ps->current_state = PWRSEQ_POWER_OFF;
> +
> +	ret = pwrseq_methods[ret].bind_method(ps);
> +	if (ret) {
> +		devres_free(ps);
> +		return ERR_PTR(ret);
> +	}
> +
> +	devres_add(dev, ps);
> +	return ps;
> +}
> +
> +static int pwrseq_of_find(struct device *dev,
> +			struct device_node **np_child,
> +			const char **power_method)
> +{
> +	struct device_node *np;
> +	const char *pm;
> +
> +	if (!dev->of_node)
> +		return -ENODEV;
> +
> +	/* Parse childnodes to find a power-method property. */
> +	for_each_child_of_node(dev->of_node, np) {
> +		if (!of_property_read_string(np, "power-method", &pm)) {
> +			*np_child = np;
> +			*power_method = pm;
> +			return 1;
> +		}
> +	}
> +
> +	return 0;
> +}
> +
> +static struct pwrseq *_devm_pwrseq_get(struct device *dev, bool optional)
> +{
> +	struct pwrseq *ps;
> +	struct device_node *np;
> +	const char *pm;
> +	int ret;
> +
> +	if (!dev)
> +		return ERR_PTR(-ENODEV);
> +
> +	ret = pwrseq_of_find(dev, &np, &pm);
> +	if (ret < 0) {
> +		return ERR_PTR(ret);
> +	} else if (ret) {
> +		ps = pwrseq_get(dev, np, pm);
> +		if (IS_ERR(ps))
> +			of_node_put(np);
> +	} else if (optional) {
> +		ps = pwrseq_get(dev, NULL, "dummy");
> +	} else {
> +		return ERR_PTR(-ENODEV);
> +	}
> +
> +	if (!IS_ERR(ps))
> +		dev_dbg(dev, "%s: Bound method=%s\n", __func__, ps->method);
> +
> +	return ps;
> +}
> +
> +struct pwrseq *devm_pwrseq_get_optional(struct device *dev)
> +{
> +	return _devm_pwrseq_get(dev, true);
> +}
> +EXPORT_SYMBOL_GPL(devm_pwrseq_get_optional);
> +
> +struct pwrseq *devm_pwrseq_get(struct device *dev)
> +{
> +	return _devm_pwrseq_get(dev, false);
> +}
> +EXPORT_SYMBOL_GPL(devm_pwrseq_get);
> +
> +static int devm_pwrseq_match(struct device *dev, void *res, void *data)
> +{
> +	struct pwrseq **ps = res;
> +
> +	return *ps == data;
> +}
> +
> +void devm_pwrseq_put(struct pwrseq *ps)
> +{
> +	devres_release(ps->dev, devm_pwrseq_release, devm_pwrseq_match, ps);
> +}
> +EXPORT_SYMBOL_GPL(devm_pwrseq_put);
> +
> +int pwrseq_select_state(struct pwrseq *ps, enum pwrseq_state ps_state)
> +{
> +	int ret = 0;
> +
> +	if (ps->current_state != ps_state)
> +		ret = ps->ps_ops->select_state(ps, ps_state);
> +
> +	if (!ret)
> +		ps->current_state = ps_state;
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(pwrseq_select_state);
> +
> +unsigned int pwrseq_supported_states(struct pwrseq *ps)
> +{
> +	return ps->supported_states;
> +}
> +EXPORT_SYMBOL_GPL(pwrseq_supported_states);
> diff --git a/drivers/pwrseq/core.h b/drivers/pwrseq/core.h
> new file mode 100644
> index 0000000..84a6449
> --- /dev/null
> +++ b/drivers/pwrseq/core.h
> @@ -0,0 +1,37 @@
> +/*
> + * Core private header for the power sequence subsystem
> + *
> + * Copyright (C) 2014 Linaro Ltd
> + *
> + * Author: Ulf Hansson <[email-masked]>
> + *
> + * License terms: GNU General Public License (GPL) version 2
> + */
> +
> +#ifndef __PWRSEQ_PWRSEQ_H
> +#define __PWRSEQ_PWRSEQ_H
> +
> +#include <linux/pwrseq.h>
> +
> +struct pwrseq_ops {
> +	int (*select_state)(struct pwrseq *, enum pwrseq_state);
> +	void (*release)(struct pwrseq *);
> +};
> +
> +struct pwrseq {
> +	struct device *dev;
> +	struct device_node *np_child;
> +	const char *method;
> +	enum pwrseq_state supported_states;
> +	enum pwrseq_state current_state;
> +	struct pwrseq_ops *ps_ops;
> +	void *data;
> +};
> +
> +struct pwrseq_method {
> +	int (*bind_method)(struct pwrseq *);
> +	const char *method;
> +};
> +
> +extern struct pwrseq_method pwrseq_methods[];
> +#endif
> diff --git a/drivers/pwrseq/method.c b/drivers/pwrseq/method.c
> new file mode 100644
> index 0000000..fe16579
> --- /dev/null
> +++ b/drivers/pwrseq/method.c
> @@ -0,0 +1,38 @@
> +/*
> + * Implements a dummy power method for power sequence subsystem
> + *
> + * Copyright (C) 2014 Linaro Ltd
> + *
> + * Author: Ulf Hansson <[email-masked]>
> + *
> + * License terms: GNU General Public License (GPL) version 2
> + */
> +
> +#include <linux/kernel.h>
> +
> +#include <linux/pwrseq.h>
> +#include "core.h"
> +
> +static int pwrseq_dummy_select_state(struct pwrseq *ps, enum pwrseq_state s)
> +{
> +	return 0;
> +}
> +
> +static void pwrseq_dummy_release(struct pwrseq *ps) { }
> +
> +static struct pwrseq_ops pwrseq_dummy_ops = {
> +	.select_state = pwrseq_dummy_select_state,
> +	.release = pwrseq_dummy_release,
> +};
> +
> +static int pwrseq_dummy_bind(struct pwrseq *ps)
> +{
> +	ps->ps_ops = &pwrseq_dummy_ops;
> +	return 0;
> +}
> +
> +/* The extern list of supported power sequence_methods */
> +struct pwrseq_method pwrseq_methods[] = {
> +	{ pwrseq_dummy_bind, "dummy" },
> +	{ NULL, NULL },
> +};
> diff --git a/include/linux/pwrseq.h b/include/linux/pwrseq.h
> new file mode 100644
> index 0000000..528b544
> --- /dev/null
> +++ b/include/linux/pwrseq.h
> @@ -0,0 +1,50 @@
> +/*
> + * Interface for the power sequence subsystem
> + *
> + * Copyright (C) 2014 Linaro Ltd
> + *
> + * Author: Ulf Hansson <[email-masked]>
> + *
> + * License terms: GNU General Public License (GPL) version 2
> + */
> +#ifndef __LINUX_PWRSEQ_PWRSEQ_H
> +#define __LINUX_PWRSEQ_PWRSEQ_H
> +
> +#include <linux/bitops.h>
> +
> +struct device;
> +struct pwrseq;
> +
> +enum pwrseq_state {
> +	PWRSEQ_POWER_OFF = BIT(0),
> +	PWRSEQ_POWER_ON = BIT(1),
> +};
> +
> +#ifdef CONFIG_OF
> +extern struct pwrseq *devm_pwrseq_get(struct device *dev);
> +extern struct pwrseq *devm_pwrseq_get_optional(struct device *dev);
> +extern void devm_pwrseq_put(struct pwrseq *ps);
> +extern int pwrseq_select_state(struct pwrseq *ps, unsigned int ps_state);
> +extern unsigned int pwrseq_supported_states(struct pwrseq *ps);
> +#else
> +static inline struct pwrseq *devm_pwrseq_get(struct device *dev)
> +{
> +	return ERR_PTR(-ENODEV);
> +}
> +static inline struct pwrseq *devm_pwrseq_get_optional(struct device *dev)
> +{
> +	return ERR_PTR(-ENODEV);
> +}
> +static inline void devm_pwrseq_put(struct pwrseq *ps) {}
> +static inline int pwrseq_select_state(struct pwrseq *ps,
> +				enum pwrseq_state ps_state)
> +{
> +	return 0;
> +}
> +static inline unsigned int pwrseq_supported_states(struct pwrseq *ps)
> +{
> +	return 0;
> +}
> +#endif
> +
> +#endif /* __LINUX_PWRSEQ_PWRSEQ_H */
>