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 17:01:37 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Kay Sievers <kay.sievers@...y.org>
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)


* Kay Sievers <kay.sievers@...y.org> wrote:

> > 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

i think that should be fixed by providing a compatible 
/proc/sys/dev/rtc/max-user-freq implementation in the new driver too.

> > 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"

but if it breaks max-user-freq (which is needed by qemu for example) 
then distros would likely disable it, right?

or this rule might be broken in some way. For example my Fedora 8 box 
has this in /etc/udev/rules.d/50-udev-default.rules:

 # miscellaneous
 KERNEL=="fuse",                 MODE="0666"
 KERNEL=="rtc|rtc0",             MODE="0644"
 KERNEL=="rtc0",                 SYMLINK+="rtc"

still i've got:

 crw------- 1 root root  10, 135 Dec 28 08:13 /dev/rtc
 crw-r--r-- 1 root root 254,   0 Dec 28 08:13 /dev/rtc0

_and_ my distro kernel doesnt even have CONFIG_RTC enabled - i run the 
Fedora 9 devel/rawhide kernel on this box:

 # CONFIG_RTC is not set
 # CONFIG_GEN_RTC is not set
 # CONFIG_HPET_RTC_IRQ is not set
 CONFIG_RTC_LIB=y
 CONFIG_RTC_CLASS=y
 # CONFIG_RTC_HCTOSYS is not set
 # CONFIG_RTC_DEBUG is not set
 # RTC interfaces
 CONFIG_RTC_INTF_SYSFS=y
 CONFIG_RTC_INTF_PROC=y
 CONFIG_RTC_INTF_DEV=y
 # CONFIG_RTC_INTF_DEV_UIE_EMUL is not set
 # CONFIG_RTC_DRV_TEST is not set

udev-116-3.fc8. Maybe i just misunderstood what the grand plan was here 
- i assumed it was to smoothly convert from old driver to new driver, 
without forcing any changes on user-space.

	Ingo
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