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Message-ID: <1492592817.2970.14.camel@pengutronix.de>
Date: Wed, 19 Apr 2017 11:06:57 +0200
From: Philipp Zabel <p.zabel@...gutronix.de>
To: Peter Rosin <peda@...ntia.se>
Cc: linux-kernel@...r.kernel.org,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Wolfram Sang <wsa@...-dreams.de>,
Rob Herring <robh+dt@...nel.org>,
Mark Rutland <mark.rutland@....com>,
Jonathan Cameron <jic23@...nel.org>,
Hartmut Knaack <knaack.h@....de>,
Lars-Peter Clausen <lars@...afoo.de>,
Peter Meerwald-Stadler <pmeerw@...erw.net>,
Jonathan Corbet <corbet@....net>, linux-i2c@...r.kernel.org,
devicetree@...r.kernel.org, linux-iio@...r.kernel.org,
linux-doc@...r.kernel.org,
Andrew Morton <akpm@...ux-foundation.org>,
Colin Ian King <colin.king@...onical.com>,
Paul Gortmaker <paul.gortmaker@...driver.com>,
kernel@...gutronix.de
Subject: Re: [PATCH v13 03/10] mux: minimal mux subsystem and gpio-based mux
controller
On Thu, 2017-04-13 at 18:43 +0200, Peter Rosin wrote:
> Add a new minimalistic subsystem that handles multiplexer controllers.
> When multiplexers are used in various places in the kernel, and the
> same multiplexer controller can be used for several independent things,
> there should be one place to implement support for said multiplexer
> controller.
>
> A single multiplexer controller can also be used to control several
> parallel multiplexers, that are in turn used by different subsystems
> in the kernel, leading to a need to coordinate multiplexer accesses.
> The multiplexer subsystem handles this coordination.
>
> This new mux controller subsystem initially comes with a single backend
> driver that controls gpio based multiplexers. Even though not needed by
> this initial driver, the mux controller subsystem is prepared to handle
> chips with multiple (independent) mux controllers.
>
> Reviewed-by: Jonathan Cameron <jic23@...nel.org>
> Signed-off-by: Peter Rosin <peda@...ntia.se>
> ---
> Documentation/driver-model/devres.txt | 8 +
> MAINTAINERS | 2 +
> drivers/Kconfig | 2 +
> drivers/Makefile | 1 +
> drivers/mux/Kconfig | 34 +++
> drivers/mux/Makefile | 6 +
> drivers/mux/mux-core.c | 422 ++++++++++++++++++++++++++++++++++
> drivers/mux/mux-gpio.c | 114 +++++++++
> include/linux/mux.h | 252 ++++++++++++++++++++
> 9 files changed, 841 insertions(+)
> create mode 100644 drivers/mux/Kconfig
> create mode 100644 drivers/mux/Makefile
> create mode 100644 drivers/mux/mux-core.c
> create mode 100644 drivers/mux/mux-gpio.c
> create mode 100644 include/linux/mux.h
>
> diff --git a/Documentation/driver-model/devres.txt b/Documentation/driver-model/devres.txt
> index efb8200819d6..e2343d9cbec7 100644
> --- a/Documentation/driver-model/devres.txt
> +++ b/Documentation/driver-model/devres.txt
> @@ -337,6 +337,14 @@ MEM
> MFD
> devm_mfd_add_devices()
>
> +MUX
> + devm_mux_chip_alloc()
> + devm_mux_chip_free()
> + devm_mux_chip_register()
> + devm_mux_chip_unregister()
> + devm_mux_control_get()
> + devm_mux_control_put()
> +
> PER-CPU MEM
> devm_alloc_percpu()
> devm_free_percpu()
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 7fc06739c8ad..591eba737678 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -8563,6 +8563,8 @@ M: Peter Rosin <peda@...ntia.se>
> S: Maintained
> F: Documentation/devicetree/bindings/mux/
> F: include/linux/dt-bindings/mux/
> +F: include/linux/mux.h
> +F: drivers/mux/
>
> MULTISOUND SOUND DRIVER
> M: Andrew Veliath <andrewtv@....net>
> diff --git a/drivers/Kconfig b/drivers/Kconfig
> index 117ca14ccf85..a7ea13e1b869 100644
> --- a/drivers/Kconfig
> +++ b/drivers/Kconfig
> @@ -204,4 +204,6 @@ source "drivers/fpga/Kconfig"
>
> source "drivers/fsi/Kconfig"
>
> +source "drivers/mux/Kconfig"
> +
> endmenu
> diff --git a/drivers/Makefile b/drivers/Makefile
> index 2eced9afba53..c0436f6dd5a9 100644
> --- a/drivers/Makefile
> +++ b/drivers/Makefile
> @@ -177,3 +177,4 @@ obj-$(CONFIG_ANDROID) += android/
> obj-$(CONFIG_NVMEM) += nvmem/
> obj-$(CONFIG_FPGA) += fpga/
> obj-$(CONFIG_FSI) += fsi/
> +obj-$(CONFIG_MULTIPLEXER) += mux/
> diff --git a/drivers/mux/Kconfig b/drivers/mux/Kconfig
> new file mode 100644
> index 000000000000..41dfe08ead84
> --- /dev/null
> +++ b/drivers/mux/Kconfig
> @@ -0,0 +1,34 @@
> +#
> +# Multiplexer devices
> +#
> +
> +menuconfig MULTIPLEXER
> + tristate "Multiplexer subsystem"
> + help
> + Multiplexer controller subsystem. Multiplexers are used in a
> + variety of settings, and this subsystem abstracts their use
> + so that the rest of the kernel sees a common interface. When
> + multiple parallel multiplexers are controlled by one single
> + multiplexer controller, this subsystem also coordinates the
> + multiplexer accesses.
> +
> + To compile the subsystem as a module, choose M here: the module will
> + be called mux-core.
> +
> +if MULTIPLEXER
> +
> +config MUX_GPIO
> + tristate "GPIO-controlled Multiplexer"
> + depends on OF && GPIOLIB
> + help
> + GPIO-controlled Multiplexer controller.
> +
> + The driver builds a single multiplexer controller using a number
> + of gpio pins. For N pins, there will be 2^N possible multiplexer
> + states. The GPIO pins can be connected (by the hardware) to several
> + multiplexers, which in that case will be operated in parallel.
> +
> + To compile the driver as a module, choose M here: the module will
> + be called mux-gpio.
> +
> +endif
> diff --git a/drivers/mux/Makefile b/drivers/mux/Makefile
> new file mode 100644
> index 000000000000..bb16953f6290
> --- /dev/null
> +++ b/drivers/mux/Makefile
> @@ -0,0 +1,6 @@
> +#
> +# Makefile for multiplexer devices.
> +#
> +
> +obj-$(CONFIG_MULTIPLEXER) += mux-core.o
> +obj-$(CONFIG_MUX_GPIO) += mux-gpio.o
> diff --git a/drivers/mux/mux-core.c b/drivers/mux/mux-core.c
> new file mode 100644
> index 000000000000..66a8bccfc3d7
> --- /dev/null
> +++ b/drivers/mux/mux-core.c
> @@ -0,0 +1,422 @@
> +/*
> + * Multiplexer subsystem
> + *
> + * Copyright (C) 2017 Axentia Technologies AB
> + *
> + * Author: Peter Rosin <peda@...ntia.se>
> + *
> + * 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.
> + */
> +
> +#define pr_fmt(fmt) "mux-core: " fmt
> +
> +#include <linux/device.h>
> +#include <linux/err.h>
> +#include <linux/export.h>
> +#include <linux/idr.h>
> +#include <linux/init.h>
> +#include <linux/module.h>
> +#include <linux/mux.h>
> +#include <linux/of.h>
> +#include <linux/of_platform.h>
> +#include <linux/slab.h>
> +
> +/*
> + * The idle-as-is "state" is not an actual state that may be selected, it
> + * only implies that the state should not be changed. So, use that state
> + * as indication that the cached state of the multiplexer is unknown.
> + */
> +#define MUX_CACHE_UNKNOWN MUX_IDLE_AS_IS
> +
> +static struct class mux_class = {
> + .name = "mux",
> + .owner = THIS_MODULE,
> +};
> +
> +static int __init mux_init(void)
> +{
> + return class_register(&mux_class);
> +}
> +
> +static DEFINE_IDA(mux_ida);
> +
> +static void mux_chip_release(struct device *dev)
> +{
> + struct mux_chip *mux_chip = to_mux_chip(dev);
> +
> + ida_simple_remove(&mux_ida, mux_chip->id);
> + kfree(mux_chip);
> +}
> +
> +static struct device_type mux_type = {
> + .name = "mux-chip",
> + .release = mux_chip_release,
> +};
> +
> +struct mux_chip *mux_chip_alloc(struct device *dev,
> + unsigned int controllers, size_t sizeof_priv)
> +{
> + struct mux_chip *mux_chip;
> + int i;
> +
> + if (WARN_ON(!dev || !controllers))
> + return NULL;
> +
> + mux_chip = kzalloc(sizeof(*mux_chip) +
> + controllers * sizeof(*mux_chip->mux) +
> + sizeof_priv, GFP_KERNEL);
> + if (!mux_chip)
> + return NULL;
> +
> + mux_chip->mux = (struct mux_control *)(mux_chip + 1);
> + mux_chip->dev.class = &mux_class;
> + mux_chip->dev.type = &mux_type;
> + mux_chip->dev.parent = dev;
> + mux_chip->dev.of_node = dev->of_node;
> + dev_set_drvdata(&mux_chip->dev, mux_chip);
> +
> + mux_chip->id = ida_simple_get(&mux_ida, 0, 0, GFP_KERNEL);
> + if (mux_chip->id < 0) {
> + pr_err("muxchipX failed to get a device id\n");
> + kfree(mux_chip);
> + return NULL;
> + }
> + dev_set_name(&mux_chip->dev, "muxchip%d", mux_chip->id);
> +
> + mux_chip->controllers = controllers;
> + for (i = 0; i < controllers; ++i) {
> + struct mux_control *mux = &mux_chip->mux[i];
> +
> + mux->chip = mux_chip;
> + init_rwsem(&mux->lock);
> + mux->cached_state = MUX_CACHE_UNKNOWN;
> + mux->idle_state = MUX_IDLE_AS_IS;
> + }
> +
> + device_initialize(&mux_chip->dev);
> +
> + return mux_chip;
> +}
> +EXPORT_SYMBOL_GPL(mux_chip_alloc);
> +
> +static int mux_control_set(struct mux_control *mux, int state)
> +{
> + int ret = mux->chip->ops->set(mux, state);
> +
> + mux->cached_state = ret < 0 ? MUX_CACHE_UNKNOWN : state;
> +
> + return ret;
> +}
> +
> +int mux_chip_register(struct mux_chip *mux_chip)
> +{
> + int i;
> + int ret;
> +
> + for (i = 0; i < mux_chip->controllers; ++i) {
> + struct mux_control *mux = &mux_chip->mux[i];
> +
> + if (mux->idle_state == mux->cached_state)
> + continue;
> +
> + ret = mux_control_set(mux, mux->idle_state);
> + if (ret < 0) {
> + dev_err(&mux_chip->dev, "unable to set idle state\n");
> + return ret;
> + }
> + }
> +
> + ret = device_add(&mux_chip->dev);
> + if (ret < 0)
> + dev_err(&mux_chip->dev,
> + "device_add failed in mux_chip_register: %d\n", ret);
> + return ret;
> +}
> +EXPORT_SYMBOL_GPL(mux_chip_register);
> +
> +void mux_chip_unregister(struct mux_chip *mux_chip)
> +{
> + device_del(&mux_chip->dev);
> +}
> +EXPORT_SYMBOL_GPL(mux_chip_unregister);
> +
> +void mux_chip_free(struct mux_chip *mux_chip)
> +{
> + if (!mux_chip)
> + return;
> +
> + put_device(&mux_chip->dev);
> +}
> +EXPORT_SYMBOL_GPL(mux_chip_free);
> +
> +static void devm_mux_chip_release(struct device *dev, void *res)
> +{
> + struct mux_chip *mux_chip = *(struct mux_chip **)res;
> +
> + mux_chip_free(mux_chip);
> +}
> +
> +struct mux_chip *devm_mux_chip_alloc(struct device *dev,
> + unsigned int controllers,
> + size_t sizeof_priv)
> +{
> + struct mux_chip **ptr, *mux_chip;
> +
> + ptr = devres_alloc(devm_mux_chip_release, sizeof(*ptr), GFP_KERNEL);
> + if (!ptr)
> + return NULL;
> +
> + mux_chip = mux_chip_alloc(dev, controllers, sizeof_priv);
> + if (!mux_chip) {
> + devres_free(ptr);
> + return NULL;
> + }
> +
> + *ptr = mux_chip;
> + devres_add(dev, ptr);
> +
> + return mux_chip;
> +}
> +EXPORT_SYMBOL_GPL(devm_mux_chip_alloc);
> +
> +static int devm_mux_chip_match(struct device *dev, void *res, void *data)
> +{
> + struct mux_chip **r = res;
> +
> + if (WARN_ON(!r || !*r))
> + return 0;
> +
> + return *r == data;
> +}
> +
> +void devm_mux_chip_free(struct device *dev, struct mux_chip *mux_chip)
> +{
> + WARN_ON(devres_release(dev, devm_mux_chip_release,
> + devm_mux_chip_match, mux_chip));
> +}
> +EXPORT_SYMBOL_GPL(devm_mux_chip_free);
> +
> +static void devm_mux_chip_reg_release(struct device *dev, void *res)
> +{
> + struct mux_chip *mux_chip = *(struct mux_chip **)res;
> +
> + mux_chip_unregister(mux_chip);
> +}
> +
> +int devm_mux_chip_register(struct device *dev,
> + struct mux_chip *mux_chip)
> +{
> + struct mux_chip **ptr;
> + int res;
> +
> + ptr = devres_alloc(devm_mux_chip_reg_release, sizeof(*ptr), GFP_KERNEL);
> + if (!ptr)
> + return -ENOMEM;
> +
> + res = mux_chip_register(mux_chip);
> + if (res) {
> + devres_free(ptr);
> + return res;
> + }
> +
> + *ptr = mux_chip;
> + devres_add(dev, ptr);
> +
> + return res;
> +}
> +EXPORT_SYMBOL_GPL(devm_mux_chip_register);
> +
> +void devm_mux_chip_unregister(struct device *dev, struct mux_chip *mux_chip)
> +{
> + WARN_ON(devres_release(dev, devm_mux_chip_reg_release,
> + devm_mux_chip_match, mux_chip));
> +}
> +EXPORT_SYMBOL_GPL(devm_mux_chip_unregister);
> +
> +int mux_control_select(struct mux_control *mux, int state)
If we let two of these race, ...
> +{
> + int ret;
> +
> + if (down_read_trylock(&mux->lock)) {
> + if (mux->cached_state == state)
> + return 0;
> + /* Sigh, the mux needs updating... */
> + up_read(&mux->lock);
... and both decide the mux needs updating ...
> + }
> +
> + /* ...or it's just contended. */
> + down_write(&mux->lock);
... then the last to get to down_write will just wait here forever (or
until the first consumer calls mux_control_deselect, which may never
happen)?
> +
> + if (mux->cached_state == state) {
> + /*
> + * Hmmm, someone else changed the mux to my liking.
> + * That makes me wonder how long I waited for nothing?
> + */
> + downgrade_write(&mux->lock);
> + return 0;
> + }
> +
> + ret = mux_control_set(mux, state);
> + if (ret < 0) {
> + if (mux->idle_state != MUX_IDLE_AS_IS)
> + mux_control_set(mux, mux->idle_state);
> +
> + up_write(&mux->lock);
> + return ret;
> + }
> +
> + downgrade_write(&mux->lock);
> +
> + return 1;
> +}
> +EXPORT_SYMBOL_GPL(mux_control_select);
I wonder if these should be called mux_control_lock/unlock instead,
which would allow for try_lock and lock_timeout variants.
regards
Philipp
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