[PATCH 1/5] Implement module aliasing for i2c to translate from device tree names

[Jon Smirl]

On 1/13/08, Jean Delvare <khali at linux-fr.org> wrote:
> On Sun, 13 Jan 2008 11:24:29 -0500, Jon Smirl wrote:
> > On 1/13/08, Jean Delvare wrote:
> > > On Sat, 12 Jan 2008 11:26:34 -0500, Jon Smirl wrote:
> > > > 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.
>
> Yes, that could be done, and I agree that it will probably be faster
> than iterative review/rework cycles between you and me. I'll free some
> cycles next week for that.
>
> > 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.
>
> Really? I didn't know that. So that's another thing that the i2c
> subsystem is not doing like the rest of the kernel? Can you please
> point me to the code that does this?

I never noticed it before either. Just do find | grep modalias in /sys
and see that every driver has a modalias attribute. It is probably
implement in drivers/base.

>
> > Standard devices don't export a 'name' attribute. To see the driver
> > name for a device in sysfs look at the 'driver' link.
>
> The driver name and the device name are different things! The "name"
> attribute that i2c devices have tells user-space the device name, not
> the driver name.

For this system my i2c device names are:
0-0050  0-0051  0-0052  0-0053
How does the name=eeprom attribute interact with this? All four of my
devices have name=eeprom. What is the name field used for in user
space?

jonsmirl at terra:/sys/bus/i2c/devices/0-0052$ ls
driver  eeprom  modalias  name  power  subsystem  uevent
jonsmirl at terra:/sys/bus/i2c/devices/0-0052$ cat name
eeprom
jonsmirl at terra:/sys/bus/i2c/devices/0-0052$ ls driver -l
lrwxrwxrwx 1 root root 0 2008-01-13 12:46 driver ->
../../../../../../bus/i2c/drivers/eeprom
jonsmirl at terra:/sys/bus/i2c/devices/0-0052$

jonsmirl at terra:/sys/bus/i2c/drivers$ ls
eeprom
jonsmirl at terra:/sys/bus/i2c/drivers$ ls eeprom
0-0050  0-0051  0-0052  0-0053  bind  module  uevent  unbind

>
> You may not like what the i2c subsystem does but you can't ignore its
> history. The name attribute of i2c devices has been there pretty much
> forever and user-space relies on it, thus we can't remove it.
>
> --
> Jean Delvare
>


-- 
Jon Smirl
jonsmirl at gmail.com