Subject: [PATCH 2/6] drivers/base: add bus for System-on-Chip devices

From: [email-masked] (Greg KH)
Date: Fri, 27 Jan 2012 17:05:34 -0800

On Sat, Jan 21, 2012 at 05:08:03PM +0000, Lee Jones wrote:
> Traditionally, any System-on-Chip based platform creates a flat list
> of platform_devices directly under /sys/devices/platform.
> 
> In order to give these some better structure, this introduces a new
> bus type for soc_devices that are registered with the new
> soc_device_register() function.  All devices that are on the same
> chip should then be registered as child devices of the soc device.
> 
> The soc bus also exports a few standardised device attributes which
> allow user space to query the specific type of soc.
> 
> Signed-off-by: Lee Jones <[email-masked]>
> ---
>  drivers/base/Kconfig    |    3 +
>  drivers/base/Makefile   |    1 +
>  drivers/base/soc.c      |  185 +++++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/sys_soc.h |   37 ++++++++++
>  4 files changed, 226 insertions(+), 0 deletions(-)
>  create mode 100644 drivers/base/soc.c
>  create mode 100644 include/linux/sys_soc.h
> 
> diff --git a/drivers/base/Kconfig b/drivers/base/Kconfig
> index 7be9f79..9aa618a 100644
> --- a/drivers/base/Kconfig
> +++ b/drivers/base/Kconfig
> @@ -176,6 +176,9 @@ config GENERIC_CPU_DEVICES
>  	bool
>  	default n
>  
> +config SOC_BUS
> +	bool

That's nice, but you do need some kind of help text here, right?

> +
>  source "drivers/base/regmap/Kconfig"
>  
>  config DMA_SHARED_BUFFER
> diff --git a/drivers/base/Makefile b/drivers/base/Makefile
> index 2c8272d..4f302a6 100644
> --- a/drivers/base/Makefile
> +++ b/drivers/base/Makefile
> @@ -19,6 +19,7 @@ obj-$(CONFIG_MODULES)	+= module.o
>  endif
>  obj-$(CONFIG_SYS_HYPERVISOR) += hypervisor.o
>  obj-$(CONFIG_REGMAP)	+= regmap/
> +obj-$(CONFIG_SOC_BUS) += soc.o
>  
>  ccflags-$(CONFIG_DEBUG_DRIVER) := -DDEBUG
>  
> diff --git a/drivers/base/soc.c b/drivers/base/soc.c
> new file mode 100644
> index 0000000..0c9e350
> --- /dev/null
> +++ b/drivers/base/soc.c
> @@ -0,0 +1,185 @@
> +/*
> + * Copyright (C) ST-Ericsson SA 2011
> + *
> + * Author: Lee Jones <[email-masked]> for ST-Ericsson.
> + * License terms:  GNU General Public License (GPL), version 2
> + */
> +
> +#include <linux/sysfs.h>
> +#include <linux/module.h>
> +#include <linux/init.h>
> +#include <linux/stat.h>
> +#include <linux/slab.h>
> +#include <linux/idr.h>
> +#include <linux/spinlock.h>
> +#include <linux/sys_soc.h>
> +#include <linux/err.h>
> +
> +static struct ida soc_ida;
> +static spinlock_t soc_lock;
> +
> +static ssize_t soc_info_get(struct device *dev,
> +			    struct device_attribute *attr,
> +			    char *buf);
> +

Why not put the whole function here, well a few lines lower, so no
forward declaration is needed, saving a few extra lines.

> +struct soc_device {
> +	struct device dev;
> +	struct soc_device_attribute *attr;

const?

> +	int soc_dev_num;

Why is this needed?  What's wrong with dev->id?

> +};
> +
> +static struct bus_type soc_bus_type = {
> +	.name  = "soc",
> +};
> +

Put the function here.

> +static DEVICE_ATTR(machine,  S_IRUGO, soc_info_get,  NULL);
> +static DEVICE_ATTR(family,   S_IRUGO, soc_info_get,  NULL);
> +static DEVICE_ATTR(soc_id,   S_IRUGO, soc_info_get,  NULL);
> +static DEVICE_ATTR(revision, S_IRUGO, soc_info_get,  NULL);
> +
> +struct device *soc_device_to_device(struct soc_device *soc_dev)
> +{
> +	return &soc_dev->dev;
> +}

Why is this even needed?  Who cares about this?

> +
> +static mode_t soc_attribute_mode(struct kobject *kobj,
> +                                 struct attribute *attr,
> +                                 int index)
> +{
> +	struct device *dev = container_of(kobj, struct device, kobj);
> +	struct soc_device *soc_dev = container_of(dev, struct soc_device, dev);
> +
> +	if ((attr == &dev_attr_machine.attr)
> +	    && (soc_dev->attr->machine != NULL))
> +		return attr->mode;
> +	if ((attr == &dev_attr_family.attr)
> +	    && (soc_dev->attr->family != NULL))
> +		return attr->mode;
> +	if ((attr == &dev_attr_revision.attr)
> +	    && (soc_dev->attr->revision != NULL))
> +		return attr->mode;
> +	if ((attr == &dev_attr_soc_id.attr)
> +	    && (soc_dev->attr->soc_id != NULL))
> +	        return attr->mode;
> +
> +	/* Unknown or unfilled attribute. */
> +	return 0;
> +}
> +
> +static ssize_t soc_info_get(struct device *dev,
> +			    struct device_attribute *attr,
> +			    char *buf)
> +{
> +	struct soc_device *soc_dev = container_of(dev, struct soc_device, dev);
> +
> +	if (attr == &dev_attr_machine)
> +		return sprintf(buf, "%s\n", soc_dev->attr->machine);
> +	if (attr == &dev_attr_family)
> +		return sprintf(buf, "%s\n", soc_dev->attr->family);
> +	if (attr == &dev_attr_revision)
> +		return sprintf(buf, "%s\n", soc_dev->attr->revision);
> +	if (attr == &dev_attr_soc_id)
> +		return sprintf(buf, "%s\n", soc_dev->attr->soc_id);
> +
> +	return -EINVAL;
> +
> +}
> +
> +static struct attribute *soc_attr[] = {
> +	&dev_attr_machine.attr,
> +	&dev_attr_family.attr,
> +	&dev_attr_soc_id.attr,
> +	&dev_attr_revision.attr,
> +	NULL,
> +};
> +
> +static const struct attribute_group soc_attr_group = {
> +	.attrs = soc_attr,
> +	.is_visible = soc_attribute_mode,

Nice, now wasn't that easier?   :)

> +};
> +
> +static const struct attribute_group *soc_attr_groups[] = {
> +	&soc_attr_group,
> +	NULL,
> +};
> +
> +static void soc_release(struct device *dev)
> +{
> +	struct soc_device *soc_dev = container_of(dev, struct soc_device, dev);
> +
> +	kfree(soc_dev);
> +}
> +
> +struct soc_device *soc_device_register(struct soc_device_attribute *soc_dev_attr)
> +{
> +	struct soc_device *soc_dev;
> +	int ret;
> +
> +	soc_dev = kzalloc(sizeof(*soc_dev), GFP_KERNEL);
> +	if (!soc_dev) {
> +	        ret = -ENOMEM;
> +		goto out1;
> +	}
> +
> +	/* Fetch a unique (reclaimable) SOC ID. */
> +	do {
> +		if (!ida_pre_get(&soc_ida, GFP_KERNEL)) {
> +			ret = -ENOMEM;
> +			goto out2;
> +		}
> +
> +		spin_lock(&soc_lock);
> +		ret = ida_get_new(&soc_ida, &soc_dev->soc_dev_num);
> +		spin_unlock(&soc_lock);
> +
> +	} while (ret == -EAGAIN);
> +
> +	if (ret)
> +	         goto out2;
> +
> +	soc_dev->attr = soc_dev_attr;
> +	soc_dev->dev.bus = &soc_bus_type;
> +	soc_dev->dev.groups = soc_attr_groups;
> +	soc_dev->dev.release = soc_release;
> +
> +	dev_set_name(&soc_dev->dev, "soc%d", soc_dev->soc_dev_num);
> +
> +	ret = device_register(&soc_dev->dev);
> +	if (ret)
> +		goto out3;
> +
> +	return soc_dev;
> +
> +out3:
> +	ida_remove(&soc_ida, soc_dev->soc_dev_num);
> +out2:
> +	kfree(soc_dev);
> +out1:
> +	return ERR_PTR(ret);
> +}
> +
> +/* Ensure soc_dev->attr is freed prior to calling soc_device_unregister. */
> +void soc_device_unregister(struct soc_device *soc_dev)
> +{
> +	ida_remove(&soc_ida, soc_dev->soc_dev_num);
> +
> +	device_unregister(&soc_dev->dev);
> +}
> +
> +static int __init soc_bus_register(void)
> +{
> +	spin_lock_init(&soc_lock);
> +
> +	ida_init(&soc_ida);
> +
> +	return bus_register(&soc_bus_type);
> +}
> +core_initcall(soc_bus_register);
> +
> +static void __exit soc_bus_unregister(void)
> +{
> +	ida_destroy(&soc_ida);
> +
> +	bus_unregister(&soc_bus_type);
> +}
> +module_exit(soc_bus_unregister);
> diff --git a/include/linux/sys_soc.h b/include/linux/sys_soc.h
> new file mode 100644
> index 0000000..2739ccb
> --- /dev/null
> +++ b/include/linux/sys_soc.h
> @@ -0,0 +1,37 @@
> +/*
> + * Copyright (C) ST-Ericsson SA 2011
> + * Author: Lee Jones <[email-masked]> for ST-Ericsson.
> + * License terms:  GNU General Public License (GPL), version 2
> + */
> +#ifndef __SOC_BUS_H
> +#define __SOC_BUS_H
> +
> +#include <linux/device.h>
> +
> +struct soc_device_attribute {
> +	const char *machine;
> +	const char *family;
> +	const char *revision;
> +	const char *soc_id;
> +};
> +
> +/**
> + * soc_device_register - register SoC as a device
> + * @soc_plat_dev_attr: Attributes passed from platform to be attributed to a SoC
> + */
> +struct soc_device *soc_device_register(
> +	struct soc_device_attribute *soc_plat_dev_attr);

const?

> +
> +/**
> + * soc_device_unregister - unregister SoC device
> + * @dev: SoC device to be unregistered
> + */
> +void soc_device_unregister(struct soc_device *soc_dev);

We need more documentation for these functions.

> +
> +/**
> + * soc_device_to_device - helper function to fetch struct device
> + * @soc: Previously registered SoC device container
> + */
> +struct device *soc_device_to_device(struct soc_device *soc);

Is the reference count incremented when this is called?  Why is this
needed at all anyway?

Overall, much nicer, but we need more documentation on how to use this
properly, and what exactly it does.

You are almost there :)

thanks,

greg k-h