linux-kernel - Re: /sys/devices/system/cpu/cpuX/online are missing

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Message-ID: <20070313095652.GB20518@flint.arm.linux.org.uk>
Date:	Tue, 13 Mar 2007 09:56:52 +0000
From:	Russell King <rmk+lkml@....linux.org.uk>
To:	Heiko Carstens <heiko.carstens@...ibm.com>,
	Andreas Schwab <schwab@...e.de>,
	Giuliano Pochini <pochini@...ise.shiny.it>,
	linuxppc-dev@...abs.org, linux-kernel@...r.kernel.org,
	Suresh Siddha <suresh.b.siddha@...el.com>
Subject: Re: /sys/devices/system/cpu/cpuX/online are missing

On Tue, Mar 13, 2007 at 09:40:39AM +0000, Russell King wrote:
> On Tue, Mar 13, 2007 at 10:11:59AM +0100, Heiko Carstens wrote:
> > On Tue, Mar 13, 2007 at 10:03:50AM +0100, Heiko Carstens wrote:
> > > I was referring to arch/ppc not arch/powerpc. But it seems that arch/ppc
> > > doesn't support cpu hotplug anyway. So I guess it's indeed just a missing
> > > config option.
> > > 
> > > Grepping a bit further shows that arm suffered by the change that inverted
> > > the logic if the 'online' attribute for cpus should appear. Since arm
> > > supports cpu hotplug but the patch left arm out, it doesn't work there
> > > anymore (cc'ing arm people: changeset 72486f1f8f0a2bc828b9d30cf4690cf2dd6807fc
> > > is most probably disabling cpu hotplug support on arm like it did on s390).
> > 
> > Should have cc'ed Suresh Siddha who caused the breakage ;)
> 
> Welcome to why cleanups are bad news. ;(  Yes, ARM also needs to be fixed
> and I'd ask that in future people doing cleanups in core code take a little
> more time to review the code before submitting patches *AND* give heads-up
> to *EVERYONE* who might be affected by the change.

Right, here's the ARM fix which is now in the ARM tree:

# Base git commit: 8b9909ded6922c33c221b105b26917780cfa497d
#	(Merge branch 'merge' of master.kernel.org:/pub/scm/linux/kernel/git/paulus/powerpc)
#
# Author:    Russell King (Tue Mar 13 09:54:21 GMT 2007)
# Committer: Russell King (Tue Mar 13 09:54:21 GMT 2007)
#   
#   [ARM] Fix breakage caused by 72486f1f8f0a2bc828b9d30cf4690cf2dd6807fc
#   
#   72486f1f8f0a2bc828b9d30cf4690cf2dd6807fc inverted the sense for
#   enabling hotplug CPU controls without reference to any other
#   architecture other than i386, ia64 and PowerPC.  This left
#   everyone else without hotplug CPU control.
#   
#   Fix ARM for this brain damage.
#   
#   Signed-off-by: Russell King
#
#    arch/arm/kernel/setup.c |    7 +++++--
#    1 files changed, 5 insertions(+), 2 deletions(-)
#
diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c
index 03e37af..0453dcc 100644
--- a/arch/arm/kernel/setup.c
+++ b/arch/arm/kernel/setup.c
@@ -839,8 +839,11 @@ static int __init topology_init(void)
 {
 	int cpu;
 
-	for_each_possible_cpu(cpu)
-		register_cpu(&per_cpu(cpu_data, cpu).cpu, cpu);
+	for_each_possible_cpu(cpu) {
+		struct cpuinfo_arm *cpuinfo = &per_cpu(cpu_data, cpu);
+		cpuinfo->cpu.hotpluggable = 1;
+		register_cpu(&cpuinfo->cpu, cpu);
+	}
 
 	return 0;
 }


-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:
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