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Date: Thu, 21 Aug 2014 13:20:47 +0200
From: David Herrmann <dh.herrmann@...il.com>
To: Sudeep Holla <sudeep.holla@....com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Kay Sievers <kay.sievers@...y.org>
Cc: LKML <linux-kernel@...r.kernel.org>,
Heiko Carstens <heiko.carstens@...ibm.com>,
Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
Stephen Boyd <sboyd@...eaurora.org>
Subject: Re: [PATCH v3 03/11] drivers: base: add new class "cpu" to group cpu devices
Hi
On Thu, Aug 21, 2014 at 12:59 PM, Sudeep Holla <sudeep.holla@....com> wrote:
> From: Sudeep Holla <sudeep.holla@....com>
>
> This patch creates a new class called "cpu" and assigns it to all the
> cpu devices. This helps in grouping all the cpu devices and associated
> child devices under the same class.
>
> This patch also:
> 1. modifies the get_parent_device to return the legacy path
> (/sys/devices/system/cpu/..) for the cpu class devices to support
> existing sysfs ABI
> 2. avoids creating link in the class directory pointing to the device as
> there would be per-cpu instance of these devices with the same name
> 3. makes sure subsystem symlink continues pointing to cpu bus instead of
> cpu class for cpu devices
This patch lacks any explanation _why_ you add a class for CPUs. With
this patch applied, these directories are effectively the same:
/sys/bus/cpu/devices/
/sys/class/cpu/
Why do we need a cpu-class if the same set of information is already
available on the cpu-bus? Furthermore, classes are deprecated anyway.
Everything you can do with a class can be solved with a bus. And we
already have a bus for cpus.
Thanks
David
> Signed-off-by: Sudeep Holla <sudeep.holla@....com>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> ---
> drivers/base/core.c | 39 +++++++++++++++++++++++++++++++++------
> drivers/base/cpu.c | 7 +++++++
> include/linux/cpu.h | 2 ++
> 3 files changed, 42 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index 20da3ad1696b..fe622e2a48d0 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -10,6 +10,7 @@
> *
> */
>
> +#include <linux/cpu.h>
> #include <linux/device.h>
> #include <linux/err.h>
> #include <linux/init.h>
> @@ -742,6 +743,12 @@ static struct kobject *get_device_parent(struct device *dev,
> return &block_class.p->subsys.kobj;
> }
> #endif
> + /*
> + * if the device is in cpu class, then use the default/legacy
> + * /sys/devices/system/cpu/.. path
> + */
> + if (dev->class == cpu_class)
> + return &parent->kobj;
>
> /*
> * If we have no parent, we live in "virtual".
> @@ -808,11 +815,17 @@ static int device_add_class_symlinks(struct device *dev)
> if (!dev->class)
> return 0;
>
> - error = sysfs_create_link(&dev->kobj,
> - &dev->class->p->subsys.kobj,
> - "subsystem");
> - if (error)
> - goto out;
> + /*
> + * the subsystem symlink in each cpu device needs to continue
> + * pointing to cpu bus
> + */
> + if (dev->bus != &cpu_subsys) {
> + error = sysfs_create_link(&dev->kobj,
> + &dev->class->p->subsys.kobj,
> + "subsystem");
> + if (error)
> + goto out;
> + }
>
> if (dev->parent && device_is_not_partition(dev)) {
> error = sysfs_create_link(&dev->kobj, &dev->parent->kobj,
> @@ -826,6 +839,13 @@ static int device_add_class_symlinks(struct device *dev)
> if (sysfs_deprecated && dev->class == &block_class)
> return 0;
> #endif
> + /*
> + * don't create a link in the cpu class directory pointing to the
> + * device as there would be per-cpu instance of these devices with
> + * the same name
> + */
> + if (dev->class == cpu_class)
> + return 0;
>
> /* link in the class directory pointing to the device */
> error = sysfs_create_link(&dev->class->p->subsys.kobj,
> @@ -851,11 +871,18 @@ static void device_remove_class_symlinks(struct device *dev)
>
> if (dev->parent && device_is_not_partition(dev))
> sysfs_remove_link(&dev->kobj, "device");
> - sysfs_remove_link(&dev->kobj, "subsystem");
> +
> + /* if subsystem points to cpu bus, bus_remove_device will remove it */
> + if (dev->bus != &cpu_subsys)
> + sysfs_remove_link(&dev->kobj, "subsystem");
> #ifdef CONFIG_BLOCK
> if (sysfs_deprecated && dev->class == &block_class)
> return;
> #endif
> + /* symlinks are not created for cpu class devices, nothing to remove */
> + if (dev->class == cpu_class)
> + return;
> +
> sysfs_delete_link(&dev->class->p->subsys.kobj, &dev->kobj, dev_name(dev));
> }
>
> diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
> index 277a9cfa9040..8e380214625d 100644
> --- a/drivers/base/cpu.c
> +++ b/drivers/base/cpu.c
> @@ -319,6 +319,7 @@ static int cpu_uevent(struct device *dev, struct kobj_uevent_env *env)
> }
> #endif
>
> +struct class *cpu_class;
> /*
> * register_cpu - Setup a sysfs device for a CPU.
> * @cpu - cpu->hotpluggable field set to 1 will generate a control file in
> @@ -335,6 +336,8 @@ int register_cpu(struct cpu *cpu, int num)
> memset(&cpu->dev, 0x00, sizeof(struct device));
> cpu->dev.id = num;
> cpu->dev.bus = &cpu_subsys;
> + cpu->dev.parent = cpu_subsys.dev_root;
> + cpu->dev.class = cpu_class;
> cpu->dev.release = cpu_device_release;
> cpu->dev.offline_disabled = !cpu->hotpluggable;
> cpu->dev.offline = !cpu_online(num);
> @@ -420,5 +423,9 @@ void __init cpu_dev_init(void)
> if (subsys_system_register(&cpu_subsys, cpu_root_attr_groups))
> panic("Failed to register CPU subsystem");
>
> + cpu_class = class_create(THIS_MODULE, "cpu");
> + if (IS_ERR(cpu_class))
> + panic("Failed to register CPU class");
> +
> cpu_dev_register_generic();
> }
> diff --git a/include/linux/cpu.h b/include/linux/cpu.h
> index 95978ad7fcdd..8c0fc9b0acad 100644
> --- a/include/linux/cpu.h
> +++ b/include/linux/cpu.h
> @@ -39,6 +39,8 @@ extern void cpu_remove_dev_attr(struct device_attribute *attr);
> extern int cpu_add_dev_attr_group(struct attribute_group *attrs);
> extern void cpu_remove_dev_attr_group(struct attribute_group *attrs);
>
> +extern struct class *cpu_class;
> +
> #ifdef CONFIG_HOTPLUG_CPU
> extern void unregister_cpu(struct cpu *cpu);
> extern ssize_t arch_cpu_probe(const char *, size_t);
> --
> 1.8.3.2
>
> --
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