linux-kernel - Re: [PATCH v2 1/9] drivers: base: add new class "cpu" to group cpu devices

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Date:	Mon, 28 Jul 2014 14:37:58 +0100
From:	Sudeep Holla <sudeep.holla@....com>
To:	Stephen Boyd <sboyd@...eaurora.org>
CC:	Sudeep Holla <sudeep.holla@....com>,
	LKML <linux-kernel@...r.kernel.org>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH v2 1/9] drivers: base: add new class "cpu" to group cpu
 devices



On 25/07/14 20:09, Stephen Boyd wrote:
> On 07/25/14 09:44, Sudeep Holla 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
>>
>> Signed-off-by: Sudeep Holla <sudeep.holla@....com>
>> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
>
> Why can't we make a 'cache' bus that the cache devices hang off of? It
> doesn't make sense to me why we would want to have cache devices living
> on the cpu bus.
>

Yes we can group them under cache, but to support legacy sysfs path
under which various cpu related information including caches, we need
to have a workaround as in this patch.

Instead of having this fixup for each class like cache, having them
grouped under cpu is better IMO and hence I added caches to cpu class.
It also helps to move few other cpu related subsystems using raw
kobjects to the device attribute groups and corresponding APIs.

Regards,
Sudeep

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