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: Russell King <rmk+kernel@armlinux.org.uk>

4 files changed, 22 insertions, 13 deletions

diff --git a/arch/arm/mach-spear/generic.h b/arch/arm/mach-spear/generic.h
index 909b97c0b237..25b4c5e66e39 100644
--- a/arch/arm/mach-spear/generic.h
+++ b/arch/arm/mach-spear/generic.h
@@ -20,6 +20,8 @@
 
 #include <asm/mach/time.h>
 
+extern volatile int spear_pen_release;
+
 extern void spear13xx_timer_init(void);
 extern void spear3xx_timer_init(void);
 extern struct pl022_ssp_controller pl022_plat_data;
diff --git a/arch/arm/mach-spear/headsmp.S b/arch/arm/mach-spear/headsmp.S
index c52192dc3d9f..6e250b6c0aa2 100644
--- a/arch/arm/mach-spear/headsmp.S
+++ b/arch/arm/mach-spear/headsmp.S
@@ -43,5 +43,5 @@ pen:	ldr	r7, [r6]
 
 	.align
 1:	.long	.
-	.long	pen_release
+	.long	spear_pen_release
 ENDPROC(spear13xx_secondary_startup)
diff --git a/arch/arm/mach-spear/hotplug.c b/arch/arm/mach-spear/hotplug.c
index 12edd1cf8a12..0dd84f609627 100644
--- a/arch/arm/mach-spear/hotplug.c
+++ b/arch/arm/mach-spear/hotplug.c
@@ -16,6 +16,8 @@
 #include <asm/cp15.h>
 #include <asm/smp_plat.h>
 
+#include "generic.h"
+
 static inline void cpu_enter_lowpower(void)
 {
 	unsigned int v;
@@ -57,7 +59,7 @@ static inline void spear13xx_do_lowpower(unsigned int cpu, int *spurious)
 	for (;;) {
 		wfi();
 
-		if (pen_release == cpu) {
+		if (spear_pen_release == cpu) {
 			/*
 			 * OK, proper wakeup, we're done
 			 */
diff --git a/arch/arm/mach-spear/platsmp.c b/arch/arm/mach-spear/platsmp.c
index 39038a03836a..b1ff4bb86f6d 100644
--- a/arch/arm/mach-spear/platsmp.c
+++ b/arch/arm/mach-spear/platsmp.c
@@ -20,16 +20,21 @@
 #include <mach/spear.h>
 #include "generic.h"
 
+/* XXX spear_pen_release is cargo culted code - DO NOT COPY XXX */
+volatile int spear_pen_release = -1;
+
 /*
- * 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 spear_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 spear_write_pen_release(int val)
 {
-	pen_release = val;
+	spear_pen_release = val;
 	smp_wmb();
-	sync_cache_w(&pen_release);
+	sync_cache_w(&spear_pen_release);
 }
 
 static DEFINE_SPINLOCK(boot_lock);
@@ -42,7 +47,7 @@ static void spear13xx_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);
+	spear_write_pen_release(-1);
 
 	/*
 	 * Synchronise with the boot thread.
@@ -64,17 +69,17 @@ static int spear13xx_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 spear_pen_release.
 	 *
-	 * Note that "pen_release" is the hardware CPU ID, whereas
+	 * Note that "spear_pen_release" is the hardware CPU ID, whereas
 	 * "cpu" is Linux's internal ID.
 	 */
-	write_pen_release(cpu);
+	spear_write_pen_release(cpu);
 
 	timeout = jiffies + (1 * HZ);
 	while (time_before(jiffies, timeout)) {
 		smp_rmb();
-		if (pen_release == -1)
+		if (spear_pen_release == -1)
 			break;
 
 		udelay(10);
@@ -86,7 +91,7 @@ static int spear13xx_boot_secondary(unsigned int cpu, struct task_struct *idle)
 	 */
 	spin_unlock(&boot_lock);
 
-	return pen_release != -1 ? -ENOSYS : 0;
+	return spear_pen_release != -1 ? -ENOSYS : 0;
 }
 
 /*