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

From: Wolfram Sang <wsa-z923LK4zBo2bacvFa/9K2g@public.gmane.org>
To: Jarkko Nikula <jarkko.nikula-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>
Cc: linux-i2c-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	alsa-devel-K7yf7f+aM1XWsZ/bQMPhNw@public.gmane.org,
	linux-acpi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	lm-sensors-GZX6beZjE8VD60Wz+7aTrA@public.gmane.org,
	Mark Brown <broonie-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
	"Rafael J. Wysocki" <rjw-LthD3rsA81gm4RdzfppkhA@public.gmane.org>,
	Jean Delvare <jdelvare-IBi9RG/b67k@public.gmane.org>,
	Liam Girdwood <lgirdwood-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>,
	Dustin Byford
	<dustin-qUQiAmfTcIp+XZJcv9eMoEEOCMrvLtNR@public.gmane.org>,
	linux-0h96xk9xTtrk1uMJSBkQmQ@public.gmane.org
Subject: Re: [RFC] i2c: Revert back to old device naming for ACPI enumerated I2C slaves
Date: Mon, 24 Aug 2015 15:26:13 +0200	[thread overview]
Message-ID: <20150824132612.GA10078@katana> (raw)
In-Reply-To: <1440413522-7855-1-git-send-email-jarkko.nikula-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>

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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.

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 :/

   Wolfram

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