Commit 6213f70e authored by Russell King's avatar Russell King
Browse files

ARM: smp: remove arch-provided "pen_release" 



Consolidating the "pen_release" stuff amongst the various SoC
implementations gives credence to having a CPU holding pen for
secondary CPUs.  However, this is far from the truth.

Many SoC implementations cargo-cult copied various bits of the pen
release implementation from the initial Realview/Versatile Express
implementation without understanding what it was or why it existed.
The reason it existed is because these are _development_ platforms,
and some board firmware is unable to individually control the
startup of secondary CPUs.  Moreover, they do not have a way to
power down or reset secondary CPUs for hot-unplug.  Hence, the
pen_release implementation was designed for ARM Ltd's development
platforms to provide a working implementation, even though it is
very far from what is required.

It was decided a while back to reduce the duplication by consolidating
the "pen_release" variable, but this only made the situation worse -
we have ended up with several implementations that read this variable
but do not write it - again, showing the cargo-cult mentality at work,
lack of proper review of new code, and in some cases a lack of testing.

While it would be preferable to remove pen_release entirely from the
kernel, this is not possible without help from the SoC maintainers,
which seems to be lacking.  However, I want to remove pen_release from
arch code to remove the credence that having it gives.

This patch removes pen_release from the arch code entirely, adding
private per-SoC definitions for it instead, and explicitly stating
that write_pen_release() is cargo-cult copied and should not be
copied any further.  Rename write_pen_release() in a similar fashion
as well.

Signed-off-by: default avatarRussell King <rmk+kernel@armlinux.org.uk>
parent 70678554

arch/arm/include/asm/smp.h

+0 −1
Original line number Diff line number Diff line
@@ -67,7 +67,6 @@ struct secondary_data { 
	void *stack;

};

extern struct secondary_data secondary_data;

extern volatile int pen_release;

extern void secondary_startup(void);

extern void secondary_startup_arm(void);

arch/arm/kernel/smp.c

+0 −6
Original line number Diff line number Diff line
@@ -62,12 +62,6 @@ 
 */

struct secondary_data secondary_data;



/*

 * control for which core is the next to come out of the secondary

 * boot "holding pen"

 */

volatile int pen_release = -1;



enum ipi_msg_type {

	IPI_WAKEUP,

	IPI_TIMER,

arch/arm/mach-exynos/headsmp.S

+1 −1
Original line number Diff line number Diff line
@@ -36,4 +36,4 @@ ENDPROC(exynos4_secondary_startup) 


	.align 2

1:	.long	.

	.long	pen_release
 
	.long	exynos_pen_release

arch/arm/mach-exynos/platsmp.c

+18 −13
Original line number Diff line number Diff line
@@ -28,6 +28,9 @@ 


extern void exynos4_secondary_startup(void);



/* XXX exynos_pen_release is cargo culted code - DO NOT COPY XXX */

volatile int exynos_pen_release = -1;



#ifdef CONFIG_HOTPLUG_CPU

static inline void cpu_leave_lowpower(u32 core_id)

{
@@ -57,7 +60,7 @@ static inline void platform_do_lowpower(unsigned int cpu, int *spurious) 


		wfi();



		if (pen_release == core_id) {

		if (exynos_pen_release == core_id) {

			/*

			 * OK, proper wakeup, we're done

			 */
@@ -228,15 +231,17 @@ void exynos_core_restart(u32 core_id) 
}



/*

 * Write pen_release in a way that is guaranteed to be visible to all

 * observers, irrespective of whether they're taking part in coherency

 * XXX CARGO CULTED CODE - DO NOT COPY XXX

 *

 * Write exynos_pen_release in a way that is guaranteed to be visible to

 * all observers, irrespective of whether they're taking part in coherency

 * or not.  This is necessary for the hotplug code to work reliably.

 */

static void write_pen_release(int val)

static void exynos_write_pen_release(int val)

{

	pen_release = val;

	exynos_pen_release = val;

	smp_wmb();

	sync_cache_w(&pen_release);

	sync_cache_w(&exynos_pen_release);

}



static DEFINE_SPINLOCK(boot_lock);
@@ -247,7 +252,7 @@ static void exynos_secondary_init(unsigned int cpu) 
	 * let the primary processor know we're out of the

	 * pen, then head off into the C entry point

	 */

	write_pen_release(-1);

	exynos_write_pen_release(-1);



	/*

	 * Synchronise with the boot thread.
@@ -322,12 +327,12 @@ static int exynos_boot_secondary(unsigned int cpu, struct task_struct *idle) 
	/*

	 * The secondary processor is waiting to be released from

	 * the holding pen - release it, then wait for it to flag

	 * that it has been released by resetting pen_release.

	 * that it has been released by resetting exynos_pen_release.

	 *

	 * Note that "pen_release" is the hardware CPU core ID, whereas

	 * Note that "exynos_pen_release" is the hardware CPU core ID, whereas

	 * "cpu" is Linux's internal ID.

	 */

	write_pen_release(core_id);

	exynos_write_pen_release(core_id);



	if (!exynos_cpu_power_state(core_id)) {

		exynos_cpu_power_up(core_id);
@@ -376,13 +381,13 @@ static int exynos_boot_secondary(unsigned int cpu, struct task_struct *idle) 
		else

			arch_send_wakeup_ipi_mask(cpumask_of(cpu));



		if (pen_release == -1)

		if (exynos_pen_release == -1)

			break;



		udelay(10);

	}



	if (pen_release != -1)

	if (exynos_pen_release != -1)

		ret = -ETIMEDOUT;



	/*
@@ -392,7 +397,7 @@ static int exynos_boot_secondary(unsigned int cpu, struct task_struct *idle) 
fail:

	spin_unlock(&boot_lock);



	return pen_release != -1 ? ret : 0;

	return exynos_pen_release != -1 ? ret : 0;

}



static void __init exynos_smp_prepare_cpus(unsigned int max_cpus)

arch/arm/mach-prima2/common.h

+2 −0
Original line number Diff line number Diff line
@@ -15,6 +15,8 @@ 
#include <asm/mach/time.h>

#include <asm/exception.h>



extern volatile int prima2_pen_release;



extern const struct smp_operations sirfsoc_smp_ops;

extern void sirfsoc_secondary_startup(void);

extern void sirfsoc_cpu_die(unsigned int cpu);

CRA Git | Maintained and supported by SUSTech CRA and CCSE