linux-kernel - Re: [PATCH 0/4] PM: Do not destroy/create devices while suspended (rev. 2)

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Date:	Wed, 2 Jan 2008 15:55:00 +0100
From:	"Kay Sievers" <kay.sievers@...y.org>
To:	"Ingo Molnar" <mingo@...e.hu>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	"pm list" <linux-pm@...ts.linux-foundation.org>,
	"ACPI Devel Maling List" <linux-acpi@...r.kernel.org>,
	"Alan Stern" <stern@...land.harvard.edu>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Len Brown" <lenb@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
	"Pavel Machek" <pavel@...e.cz>, "Greg KH" <gregkh@...e.de>,
	"David Brownell" <david-b@...bell.net>
Subject: Re: [PATCH 0/4] PM: Do not destroy/create devices while suspended (rev. 2)

On Jan 2, 2008 2:15 PM, Ingo Molnar <mingo@...e.hu> wrote:
> A stupid question. The old RTC driver is in
> drivers/char/rtc.c, and maps to:
>
>   crw-r--r-- 1 root root  10, 135 Oct 25 18:02 /dev/rtc
>
> the new driver is in drivers/rtc/*, and maps to:
>
>   crw-r--r-- 1 root root 254,   0 Dec 12 02:30 /dev/rtc0
>
> but all the x86 distro boxes i have access to make use of /dev/rtc.
> There's no symlink set up from /dev/rtc to /dev/rtc0 either. So it
> appears to me that the new RTC driver isnt actually utilized on most
> distributions.
>
> shouldnt we provide a Kconfig way of replacing dev 10:135 with the new
> driver's 254:0 device? (while keeping all the current modes of operation
> as well, of course.) It's all supposed to be 100% ioctl ABI compatible
> with the old driver, right?

It's not compatible enough to "fake" only the old major/minor. Userspace
must be fixed not to depend on stuff like:  /proc/sys/dev/rtc/max-user-freq:
  http://lkml.org/lkml/2007/8/4/183

> That way distros could start migrating to it
> as well, without depending on any udev hackery.

It's in the default udev setup:
  KERNEL=="rtc|rtc0",             MODE="0644"
  KERNEL=="rtc0",                 SYMLINK+="rtc"

Kay
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