linux-kernel - Re: 2.6.31-rc2+: Interrupts enabled after cpufreq

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Date:	Fri, 10 Jul 2009 15:25:11 -0400
From:	Dave Jones <davej@...hat.com>
To:	Marcin Slusarz <marcin.slusarz@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Linux PM List <linux-pm@...ts.linux-foundation.org>,
	cpufreq@...r.kernel.org,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: 2.6.31-rc2+: Interrupts enabled after cpufreq_suspend

On Thu, Jul 09, 2009 at 05:44:52PM +0200, Marcin Slusarz wrote:
 > I find this message after resume from s2ram:
 > [  133.014802] ------------[ cut here ]------------
 > [  133.014814] WARNING: at drivers/base/sys.c:411 sysdev_suspend+0xd3/0x27b()
 > [  133.014819] Hardware name: To Be Filled By O.E.M.
 > [  133.014828] Interrupts enabled after cpufreq_suspend+0x0/0xfd
 > [  133.014832] Modules linked in:
 > [  133.014840] Pid: 6569, comm: s2ram Not tainted 2.6.31-rc2-faf80-wusb54gc #139
 > [  133.014845] Call Trace:
 > [  133.014853]  [<ffffffff8126960a>] ? sysdev_suspend+0xd3/0x27b
 > [  133.014864]  [<ffffffff810388a9>] warn_slowpath_common+0x77/0xa4
 > [  133.014873]  [<ffffffff8103894b>] warn_slowpath_fmt+0x64/0x66
 > [  133.014883]  [<ffffffff8101ac71>] ? query_values_on_cpu+0x0/0x19
 > [  133.014892]  [<ffffffff813273bc>] ? cpufreq_suspend+0x0/0xfd
 > [  133.014900]  [<ffffffff811e6d35>] ? kobject_put+0x47/0x4b
 > [  133.014908]  [<ffffffff813269fd>] ? cpufreq_cpu_put+0x1f/0x21
 > [  133.014917]  [<ffffffff813274ac>] ? cpufreq_suspend+0xf0/0xfd
 > [  133.014926]  [<ffffffff8105aeda>] ? trace_hardirqs_off+0xd/0xf
 > [  133.014934]  [<ffffffff8126960a>] sysdev_suspend+0xd3/0x27b
 > [  133.014944]  [<ffffffff81068fd8>] suspend_devices_and_enter+0xca/0x14d
 > [  133.014952]  [<ffffffff81069114>] enter_state+0xb9/0xec
 > [  133.014959]  [<ffffffff81068923>] state_store+0xb7/0xd7
 > [  133.014967]  [<ffffffff811e6b4b>] kobj_attr_store+0x17/0x19
 > [  133.014976]  [<ffffffff811094b1>] sysfs_write_file+0xe4/0x119
 > [  133.014985]  [<ffffffff810b9f57>] vfs_write+0xac/0x164
 > [  133.014991]  [<ffffffff810ba0d3>] sys_write+0x47/0x6e
 > [  133.015000]  [<ffffffff8100aee8>] system_call_fastpath+0x16/0x1b
 > [  133.015006] ---[ end trace 470f36a1cfb444d7 ]---

powernow-k8's ->get is calling smp_call_function_single which enables interrupts.

So I couldn't help wondering... why are we caring so much about the current cpu
speed when we ->suspend anyway ? Why is cpufreq_suspend doing those gymnastics at all,
instead of just doing nothing at suspend time, and just setting the frequency
to maximum speed on resume ?

The answer seems to be in 42d4dc3f4e1ec1396371aac89d0dccfdd977191b
which introduced all this code to work around some failure that only happens
on PPC...

    [PATCH] Add suspend method to cpufreq core
    
    In order to properly fix some issues with cpufreq vs. sleep on
    PowerBooks, I had to add a suspend callback to the pmac_cpufreq driver.
    I must force a switch to full speed before sleep and I switch back to
    previous speed on resume.


Ben, is there something better we can do here ?

I really don't want to add an #ifdef __powerpc__ to core code if we can help it.
I'd rather we didn't call into driver guts at all from the suspend path.

	Dave

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