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, 15 insertions, 9 deletions

diff --git a/arch/arm/mach-prima2/common.h b/arch/arm/mach-prima2/common.h
index 6d77b622d1685..457eb7b181600 100644
--- a/arch/arm/mach-prima2/common.h
+++ b/arch/arm/mach-prima2/common.h
@@ -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);
diff --git a/arch/arm/mach-prima2/headsmp.S b/arch/arm/mach-prima2/headsmp.S
index 209d9fc5c16cf..6cf4fc60347b5 100644
--- a/arch/arm/mach-prima2/headsmp.S
+++ b/arch/arm/mach-prima2/headsmp.S
@@ -34,4 +34,4 @@ ENDPROC(sirfsoc_secondary_startup)
 
         .align
 1:      .long   .
-        .long   pen_release
+        .long   prima2_pen_release
diff --git a/arch/arm/mach-prima2/hotplug.c b/arch/arm/mach-prima2/hotplug.c
index a728c78b996f7..b6cf1527e3309 100644
--- a/arch/arm/mach-prima2/hotplug.c
+++ b/arch/arm/mach-prima2/hotplug.c
@@ -11,6 +11,7 @@
 #include <linux/smp.h>
 
 #include <asm/smp_plat.h>
+#include "common.h"
 
 static inline void platform_do_lowpower(unsigned int cpu)
 {
@@ -18,7 +19,7 @@ static inline void platform_do_lowpower(unsigned int cpu)
 	for (;;) {
 		__asm__ __volatile__("dsb\n\t" "wfi\n\t"
 			: : : "memory");
-		if (pen_release == cpu_logical_map(cpu)) {
+		if (prima2_pen_release == cpu_logical_map(cpu)) {
 			/*
 			 * OK, proper wakeup, we're done
 			 */
diff --git a/arch/arm/mach-prima2/platsmp.c b/arch/arm/mach-prima2/platsmp.c
index 75ef5d4be554c..d1f8b5168083c 100644
--- a/arch/arm/mach-prima2/platsmp.c
+++ b/arch/arm/mach-prima2/platsmp.c
@@ -24,13 +24,16 @@ static void __iomem *clk_base;
 
 static DEFINE_SPINLOCK(boot_lock);
 
+/* XXX prima2_pen_release is cargo culted code - DO NOT COPY XXX */
+volatile int prima2_pen_release = -1;
+
 static void sirfsoc_secondary_init(unsigned int cpu)
 {
 	/*
 	 * let the primary processor know we're out of the
 	 * pen, then head off into the C entry point
 	 */
-	pen_release = -1;
+	prima2_pen_release = -1;
 	smp_wmb();
 
 	/*
@@ -80,13 +83,13 @@ static int sirfsoc_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 prima2_pen_release.
 	 *
-	 * Note that "pen_release" is the hardware CPU ID, whereas
+	 * Note that "prima2_pen_release" is the hardware CPU ID, whereas
 	 * "cpu" is Linux's internal ID.
 	 */
-	pen_release = cpu_logical_map(cpu);
-	sync_cache_w(&pen_release);
+	prima2_pen_release = cpu_logical_map(cpu);
+	sync_cache_w(&prima2_pen_release);
 
 	/*
 	 * Send the secondary CPU SEV, thereby causing the boot monitor to read
@@ -97,7 +100,7 @@ static int sirfsoc_boot_secondary(unsigned int cpu, struct task_struct *idle)
 	timeout = jiffies + (1 * HZ);
 	while (time_before(jiffies, timeout)) {
 		smp_rmb();
-		if (pen_release == -1)
+		if (prima2_pen_release == -1)
 			break;
 
 		udelay(10);
@@ -109,7 +112,7 @@ static int sirfsoc_boot_secondary(unsigned int cpu, struct task_struct *idle)
 	 */
 	spin_unlock(&boot_lock);
 
-	return pen_release != -1 ? -ENOSYS : 0;
+	return prima2_pen_release != -1 ? -ENOSYS : 0;
 }
 
 const struct smp_operations sirfsoc_smp_ops __initconst = {