Re: [PATCH] drivers: base: add cpu_device_create to support per-cpu devices

[David Herrmann <dh.herrmann@gmail.com>]

Hi

On Fri, Aug 22, 2014 at 1:29 PM, Sudeep Holla <sudeep.holla@arm.com> wrote:
> From: Sudeep Holla <sudeep.holla@arm.com>
>
> This patch adds a new function to create per-cpu devices.
> This helps in:
> 1. reusing the device infrastructure to create any cpu related
>    attributes and corresponding sysfs instead of creating and
>    dealing with raw kobjects directly
> 2. retaining the legacy path(/sys/devices/system/cpu/..) to support
>    existing sysfs ABI
> 3. avoiding to create links in the bus directory pointing to the
>    device as there would be per-cpu instance of these devices with
>    the same name since dev->bus is not populated to cpu_sysbus on
>    purpose
>
> Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> ---
>  drivers/base/cpu.c  | 54 +++++++++++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/cpu.h |  4 ++++
>  2 files changed, 58 insertions(+)
>
> Hi Greg,
>
> Here is the alternate solution I could come up with instead of
> creating cpu class. cpu_device_create is very similar to
> device_create_groups_vargs w/o class support, but I could not
> reuse anything else to avoid creating similar function.
>
> Let me know your thoughts/suggestions on this.
>
> Regards,
> Sudeep
>
>
> diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
> index 277a9cfa9040..53f0c4141d05 100644
> --- a/drivers/base/cpu.c
> +++ b/drivers/base/cpu.c
> @@ -363,6 +363,60 @@ struct device *get_cpu_device(unsigned cpu)
>  }
>  EXPORT_SYMBOL_GPL(get_cpu_device);
>
> +static void device_create_release(struct device *dev)
> +{
> +       kfree(dev);
> +}
> +
> +static struct device *
> +__cpu_device_create(struct device *parent, void *drvdata,
> +                   const struct attribute_group **groups,
> +                   const char *fmt, va_list args)
> +{
> +       struct device *dev = NULL;
> +       int retval = -ENODEV;
> +
> +       dev = kzalloc(sizeof(*dev), GFP_KERNEL);
> +       if (!dev) {
> +               retval = -ENOMEM;
> +               goto error;
> +       }
> +
> +       device_initialize(dev);
> +       dev->parent = parent;
> +       dev->groups = groups;
> +       dev->release = device_create_release;
> +       dev_set_drvdata(dev, drvdata);
> +
> +       retval = kobject_set_name_vargs(&dev->kobj, fmt, args);
> +       if (retval)
> +               goto error;
> +
> +       retval = device_add(dev);
> +       if (retval)
> +               goto error;

Exactly! As I said, simply setting dev->groups before calling device_add().

However, I really don't understand why we need this as global API.
Skimming over the other patches, you use cpu_device_create() only in
one place. Why not hard-code this all there? It is totally OK to do
device initialization in drivers. All the helpers (like
device_create(), device_create_with_groups(), and so on) are just
convenience functions. The driver-core API explicitly allows drivers
to initialize devices manually.

Nevertheless, this patch looks fine.

Thanks
David

> +
> +       return dev;
> +
> +error:
> +       put_device(dev);
> +       return ERR_PTR(retval);
> +}
> +
> +struct device *cpu_device_create(struct device *parent, void *drvdata,
> +                                const struct attribute_group **groups,
> +                                const char *fmt, ...)
> +{
> +       va_list vargs;
> +       struct device *dev;
> +
> +       va_start(vargs, fmt);
> +       dev = __cpu_device_create(parent, drvdata, groups, fmt, vargs);
> +       va_end(vargs);
> +       return dev;
> +}
> +EXPORT_SYMBOL_GPL(cpu_device_create);
> +
>  #ifdef CONFIG_GENERIC_CPU_AUTOPROBE
>  static DEVICE_ATTR(modalias, 0444, print_cpu_modalias, NULL);
>  #endif
> diff --git a/include/linux/cpu.h b/include/linux/cpu.h
> index 95978ad7fcdd..bb790a5621c0 100644
> --- a/include/linux/cpu.h
> +++ b/include/linux/cpu.h
> @@ -19,6 +19,7 @@
>
>  struct device;
>  struct device_node;
> +struct attribute_group;
>
>  struct cpu {
>         int node_id;            /* The node which contains the CPU */
> @@ -39,6 +40,9 @@ 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 device *cpu_device_create(struct device *parent, void *drvdata,
> +                                       const struct attribute_group **groups,
> +                                       const char *fmt, ...);
>  #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
>