Re: [RFC] i2c: Revert back to old device naming for ACPI enumerated I2C slaves

["Rafael J. Wysocki" <rjw@rjwysocki.net>]

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On Monday, August 24, 2015 03:26:13 PM Wolfram Sang wrote:
> On Mon, Aug 24, 2015 at 01:52:02PM +0300, Jarkko Nikula wrote:
> > Commit 70762abb9f89 ("i2c: Use stable dev_name for ACPI enumerated I2C
> > slaves") broke the lm-sensors which relies on I2C hwmon slave devices under
> > /sys/bus/i2c/devices/ to be named as "x-00yz". However if those hwmon
> > devices are ACPI 5 enumerated their name became "i2c-INTABCD:ij" and sysfs
> > code in lm-sensors does not find them anymore:
> > 
> > lib/sysfs.c:665:
> > if ((!subsys || !strcmp(subsys, "i2c")) &&
> >     sscanf(dev_name, "%hd-%x", &entry.chip.bus.nr,
> > 	   &entry.chip.addr) == 2) {
> > 
> > This patch fixes this by reverting back the old device naming in i2c-core
> > but at the same avoids regression to ALSA SoC drivers that depend on stable
> > device binding.
> 
> This way we fix some userspace by going back. However, this name change
> was effective for 18 months, so enough time for some other userspace to
> adapt. We would break the latter by reverting.

Right.

Generally, reverts of such things need to be made relatively quickly.

> I tend to create the symlinks to prevent any further breakage. I am open
> for other suggestions, though. This ugly situation has surely happened
> before somewhere somewhen in the kernel :/

It happens on a regular basis.

In this particular case it looks like we need a mechanism to use the old
naming scheme for hwmon and the new one for everything else or something
similar.  I'm afraid I am not familiar enough with the i2c core to suggest
anything specific ATM, though.

Thanks,
Rafael

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