Re: [PATCH v3 03/11] drivers: base: add new class "cpu" to group cpu devices

[Kay Sievers]

On Thu, Aug 21, 2014 at 2:30 PM, Sudeep Holla <sudeep.holla@xxxxxxx> wrote:
> On 21/08/14 12:20, David Herrmann wrote:
>> On Thu, Aug 21, 2014 at 12:59 PM, Sudeep Holla <sudeep.holla@xxxxxxx>
>> wrote:
>>>
>>> From: Sudeep Holla <sudeep.holla@xxxxxxx>
>>>
>>> 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/
>>
>
> Yes that's the intention, so that we don't break any existing sysfs/ABI
>
>
>> 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.
>>
>
> This was suggested[1] by GregKH. The main reason it was added is to
> reuse the device attributes rather than creating the raw kobjects.
>
> It helps to move few other cpu related subsystems using raw kobjects to
> the device attribute groups.

No, nothing should ever create a bus and a class with the same name.
This is not supported by userspace tools.

Your problem needs to be addressed by adding things to the existing
"cpu" bus, not by adding a new class.

Kay
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