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 14:15:29 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	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)

(David Brownell Cc:-ed too)

* Rafael J. Wysocki <rjw@...k.pl> wrote:

> Well, we have the following test script in the userland suspend 
> package that is supposed to work right now:
> 
> #!/bin/bash
> date
> cd /sys/class/rtc/rtc0
> echo $(( $(cat since_epoch) + 20 )) > wakealarm
> s2ram
> date
> 
> provided that the new rtc driver code is compiled (and the old one is not).

ok, will try that. 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? That way distros could start migrating to it 
as well, without depending on any udev hackery.

> > That way any suspend breakage would be detectable (and bisectable) 
> > in automated testing - if the resume does not come back after 10-20 
> > seconds then the test failed.
> 
> Yes, but please note that some systems require user space 
> manipulations of the graphics adapter for suspend to work and to 
> detect a breakage of such a system you need to boot it into X and use 
> s2ram to suspend.

yeah, i wouldnt expect graphics mode to come back without quirks. But it 
should still work fine over the network, right? (which is my main mode 
of testing anyway)

	Ingo
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