[RFC PATCH 2.6.12-rc2-mm2 0/2] i2c: new sysfs class "hwmon"

Mark M. Hoffman mhoffman at lightlink.com
Wed Apr 13 06:22:10 CEST 2005

Hi Greg, thanks for your advice:

* Greg KH <greg at kroah.com> [2005-04-12 14:55:55 -0700]:
> On Mon, Apr 11, 2005 at 12:44:27AM -0400, Mark M. Hoffman wrote:
> > Hi Khali, Greg, et. al:
> > 
> > After a brief chat w/ Khali last week (and some reading LDDv3) I did these
> > patches.  The result for me looks like this:
> > 
> > /sys/class/hwmon/1-0290/device/ -> /sys/devices/platform/i2c-1/1-0290
> > 
> > Notes/Questions:
> First a question from me, why?  What are you trying to do here?  Who
> will be using the hwmon class?  And what for?  Will all "sensor-like"
> sysfs files move to this new class, or is it just to enable userspace to
> be able to find the hwmon devices easier?

Khali is working on patches to get rid of the i2c-isa 'pseudo-adapter'.
Since any sensor chip attached to the ISA bus will no longer appear in
the /sys/bus/i2c tree, a new way is needed.  Userspace tools can be
taught to look in /sys/class/hwmon first, and then /sys/bus/i2c for

> > 1. I don't like "1-0290" for a class ID, but it was the easiest thing to
> > use at the time.  A better name might be w83627thf-0.
> As long as it's unique, that's the only requirement.

I just strlcpy'd the '1-0290' ID from the /sys/bus/i2c tree because it
is unique.  My concern is that it's not very descriptive.

> > 2. The kernel complains if I don't provide a class::release function, but
> > I can't really see a need for it in this case.  If I hold a file open through
> > the /sys/class/hwmon/X/device/Y link and then try to rmmod the driver, the 
> > rmmod will sleep until I close the file just as I expect.  Any hints here
> > Greg?
> Ick, yes, you _must_ have a release function.  _Please_ listen to the
> kernel, it isn't saying those things for no reason...  If you add a file
> to the class device, and do not have a release function, then you can

But... I didn't add any files to the class device. ;)  I'm not planning
to move any existing files (temp1_input, etc) - I just want the link
back to the device.  It didn't look like that (by itself) should require
a release function, but I'll go back and read it again.

> have a memory leak.  The way that you use the class device owned by a
> different device is not safe, nor a good idea.  I recommend using the

Err... what about struct i2c_adapter?

> "class_device_create()" function that has been added to the -mm tree (or
> the class_simple stuff that's in mainline, if you want an idea of what
> it is.  Hm, no that will not quite work, that's why I wrote the
> class_device_create() call...use that.)

OK, I'll try it again that way.

> > 3. I added the struct class_device to struct i2c_client.  This makes it
> > slightly easier to modify the sensors drivers... but not all i2c_clients
> > will need it (bloat).  It could be added to each struct <driver>_data
> > (e.g. w83627hf_data) instead.
> Use a pointer instead, and the class_device_create function.


Thanks and regards,

Mark M. Hoffman
mhoffman at lightlink.com

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