Commit 7fa22bd5 authored by Stephen Boyd's avatar Stephen Boyd Committed by Russell King
Browse files

ARM: 6993/1: platsmp: Allow secondary cpu hotplug with maxcpus=1 



If an ARM system has multiple cpus in the same socket and the
kernel is booted with maxcpus=1, secondary cpus are possible but
not present due to how platform_smp_prepare_cpus() is called.
Since most typical ARM processors don't actually support physical
hotplug, initialize the present map to be equal to the possible
map in generic ARM SMP code. Also, always call
platform_smp_prepare_cpus() as long as max_cpus is non-zero (0
means no SMP) to allow platform code to do any SMP setup.

After applying this patch it's possible to boot an ARM system
with maxcpus=1 on the command line and then hotplug in secondary
cpus via sysfs. This is more in line with how x86 does things.

Signed-off-by: default avatarStephen Boyd <sboyd@codeaurora.org>
Cc: Paul Mundt <lethal@linux-sh.org>
Cc: Kukjin Kim <kgene.kim@samsung.com>
Cc: David Brown <davidb@codeaurora.org>
Cc: Tony Lindgren <tony@atomide.com>
Cc: Srinidhi Kasagar <srinidhi.kasagar@stericsson.com>
Cc: Linus Walleij <linus.walleij@stericsson.com>
Signed-off-by: default avatarRussell King <rmk+kernel@arm.linux.org.uk>
parent 10cdc7e5

arch/arm/kernel/smp.c

+9 −2
Original line number Diff line number Diff line
@@ -361,14 +361,21 @@ void __init smp_prepare_cpus(unsigned int max_cpus) 
	 */

	if (max_cpus > ncores)

		max_cpus = ncores;



	if (max_cpus > 1) {

	if (ncores > 1 && max_cpus) {

		/*

		 * Enable the local timer or broadcast device for the

		 * boot CPU, but only if we have more than one CPU.

		 */

		percpu_timer_setup();



		/*

		 * Initialise the present map, which describes the set of CPUs

		 * actually populated at the present time. A platform should

		 * re-initialize the map in platform_smp_prepare_cpus() if

		 * present != possible (e.g. physical hotplug).

		 */

		init_cpu_present(&cpu_possible_map);



		/*

		 * Initialise the SCU if there are more than one CPU

		 * and let them know where to start.

arch/arm/mach-exynos4/platsmp.c

+0 −8
Original line number Diff line number Diff line
@@ -154,14 +154,6 @@ void __init smp_init_cpus(void) 


void __init platform_smp_prepare_cpus(unsigned int max_cpus)

{

	int i;



	/*

	 * Initialise the present map, which describes the set of CPUs

	 * actually populated at the present time.

	 */

	for (i = 0; i < max_cpus; i++)

		set_cpu_present(i, true);



	scu_enable(scu_base_addr());

arch/arm/mach-msm/platsmp.c

+0 −8
Original line number Diff line number Diff line
@@ -157,12 +157,4 @@ void __init smp_init_cpus(void) 


void __init platform_smp_prepare_cpus(unsigned int max_cpus)

{

	int i;



	/*

	 * Initialise the present map, which describes the set of CPUs

	 * actually populated at the present time.

	 */

	for (i = 0; i < max_cpus; i++)

		set_cpu_present(i, true);

}

arch/arm/mach-omap2/omap-smp.c

+0 −8
Original line number Diff line number Diff line
@@ -125,14 +125,6 @@ void __init smp_init_cpus(void) 


void __init platform_smp_prepare_cpus(unsigned int max_cpus)

{

	int i;



	/*

	 * Initialise the present map, which describes the set of CPUs

	 * actually populated at the present time.

	 */

	for (i = 0; i < max_cpus; i++)

		set_cpu_present(i, true);



	/*

	 * Initialise the SCU and wake up the secondary core using

arch/arm/mach-realview/platsmp.c

+0 −8
Original line number Diff line number Diff line
@@ -68,14 +68,6 @@ void __init smp_init_cpus(void) 


void __init platform_smp_prepare_cpus(unsigned int max_cpus)

{

	int i;



	/*

	 * Initialise the present map, which describes the set of CPUs

	 * actually populated at the present time.

	 */

	for (i = 0; i < max_cpus; i++)

		set_cpu_present(i, true);



	scu_enable(scu_base_addr());

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