On 1/13/08, Jean Delvare [off-list ref] wrote:

Hi Jon,

On Sat, 12 Jan 2008 11:26:34 -0500, Jon Smirl wrote:

quoted

The common scheme used elsewhere in the kernel for handling more than
one device in a single driver is aliases. The i2c code's existing
driver_name/type combination is a different way of implementing the
same feature. But there is no real need for driver_name/type on any
platform if aliases are used. Back in version 10 or 11 I had code in
there which replaced the two fields with aliases on all platforms but
too many people objected so I removed it..

While I agree that aliases make i2c_client.driver_name obsolete,
i2c_client.type is still needed. Not for device/driver matching in the
kernel, granted, but for device identification from userspace. This is
a first problem your patch has: when using your aliasing mechanism, the
type string is left empty. i2c-core exports this value to user-space
via the "name" sysfs attribute, and some libraries and applications
make use of it. I know of libsensors at least, but I guess there are
more. I can't apply your patch until this problem is solved, otherwise
we would break some user-space applications.

quoted

IMHO, driver_name/type should be removed in new style drivers and
replaced with aliases on all platforms since aliases are the standard
kernel mechanism.

I agree. But we can take your aliasing code now (once you have
addressed the issues I raised) and convert the users of driver_name
later; it doesn't have to be done all at once.

GregKH, adding a new dynamically loadable subsystem is not something
that happens every day, can you check to make sure all of the standard
kernels mechanisms are being used? I'm not totally sure how the
modalias naming code is supposed to be done. The subsystem core code
in these patches needs review.

Jean, could you take over the i2c core portion of the patch? That will
let you decide exactly how you want the driver_name/name fields to be
dealt with. After you get standard naming support into i2c core I'll
rework the rest of the patch to use your new code.

I don't think driver_name/name fields should be stored in an i2c
structure at all. They are redundant with the standard mechanism.

The kernel automatically exposes modalias as a sysfs attribute so the
string must be recorded further down in the driver support layers. No
need to keep a copy in the i2c structure.

Standard devices don't export a 'name' attribute. To see the driver
name for a device in sysfs look at the 'driver' link.

The second problem I have with your patch is that you make use of the
driver_name field, while I ultimately want to get rid of it. I'd rather
see you use a different field for aliases, so that the later removal of
the driver_name field and the associated mechanism is easier.

A third, related problem, is the contents of the modalias file when
using your patch. When I tested on my ADM1032 evaluation board, the
modalias contained "adm1032". This isn't a valid module alias string:
"modprobe adm1032" doesn't work. What works is "modprobe i2c:Nadm1032"
so the modalias file should contain "i2c:Nadm1032". Just take a look at
all modalias files in /sys, they all include the subsystem prefix and a
simple modprobe `cat modalias` loads the required driver. I fail to see
why the i2c subsystem would be different.

I said this is related to the second problem because right now,
i2c-core can't easily differentiate between driver names and aliases,
as both are stored in i2c_client.driver_name. Having separate fields
would make it possible (and relatively easy) to add the required prefix
before aliases but not before driver names. The only drawback is that
it will increase the size of the i2c_client structure, but I do not
care that much given that it is only temporary.

--
Jean Delvare

-- 
Jon Smirl
jonsmirl@gmail.com