Normally, when a CPU wants to clear a cache line to zero in the external L2 cache, it would generate bus cycles to write each word as it would do with any other data access.

However, a Cortex A9 connected to a L2C-310 has a specific feature where the CPU can detect this operation, and signal that it wants to zero an entire cache line. This feature, known as Full Line of Zeros (FLZ), involves a non-standard AXI signalling mechanism which only the L2C-310 can properly interpret.

There are separate enable bits in both the L2C-310 and the Cortex A9 - the L2C-310 needs to be enabled and have the FLZ enable bit set in the auxiliary control register before the Cortex A9 has this feature enabled.

Unfortunately, the suspend code was not respecting this - it's not obvious from the code:

swsusp_arch_suspend()
cpu_suspend() /* saves the Cortex A9 auxiliary control register */
arch_save_image()
soft_restart() /* turns off FLZ in Cortex A9, and disables L2C */
cpu_resume() /* restores the Cortex A9 registers, inc auxcr */

At this point, we end up with the L2C disabled, but the Cortex A9 with FLZ enabled - which means any memset() or zeroing of a full cache line will fail to take effect.

A similar issue exists in the resume path, but it's slightly more complex:

swsusp_arch_suspend()
cpu_suspend() /* saves the Cortex A9 auxiliary control register */
arch_save_image() /* image with A9 auxcr saved */
...
swsusp_arch_resume()
call_with_stack()
arch_restore_image() /* restores image with A9 auxcr saved above */ soft_restart() /* turns off FLZ in Cortex A9, and disables L2C */
cpu_resume() /* restores the Cortex A9 registers, inc auxcr */

Again, here we end up with the L2C disabled, but Cortex A9 FLZ enabled.

There's no need to turn off the L2C in either of these two paths; there are benefits from not doing so - for example, the page copies will be faster with the L2C enabled.

Hence, fix this by providing a variant of soft_restart() which can be used without turning the L2 cache controller off, and use it in both of these paths to keep the L2C enabled across the respective resume transitions.

Fixes 8ef418c7178f ("ARM: l2c: trial at enabling some Cortex-A9 optimisations")

Reported-by Sean Cross <[email protected]>

Tested-by Sean Cross <[email protected]>

Signed-off-by Russell King <[email protected]>

Signed-off-by Greg Kroah-Hartman <[email protected]>

---
 arch/arm/kernel/hibernate.c |    5 +++--
 arch/arm/kernel/process.c   |   10 ++++++++--
 arch/arm/kernel/reboot.h    |    6 ++++++
 3 files changed, 17 insertions(+), 4 deletions(-)

arch/arm/kernel/hibernate.c +3 -2

@@ -22,6 +22,7 @@
 #include <asm/suspend.h>
 #include <asm/memory.h>
 #include <asm/sections.h>
+#include "reboot.h"
 
 int pfn_is_nosave(unsigned long pfn)
 {

@@ -61,7 +62,7 @@ static int notrace arch_save_image(unsig
 
 	ret = swsusp_save();
 	if (ret == 0)
-		soft_restart(virt_to_phys(cpu_resume));
+		_soft_restart(virt_to_phys(cpu_resume), false);
 	return ret;
 }

@@ -86,7 +87,7 @@ static void notrace arch_restore_image(v
 	for (pbe = restore_pblist; pbe; pbe = pbe->next)
 		copy_page(pbe->orig_address, pbe->address);
 
-	soft_restart(virt_to_phys(cpu_resume));
+	_soft_restart(virt_to_phys(cpu_resume), false);
 }
 
 static u64 resume_stack[PAGE_SIZE/2/sizeof(u64)] __nosavedata;

arch/arm/kernel/process.c +8 -2

@@ -41,6 +41,7 @@
 #include <asm/system_misc.h>
 #include <asm/mach/time.h>
 #include <asm/tls.h>
+#include "reboot.h"
 
 #ifdef CONFIG_CC_STACKPROTECTOR
 #include <linux/stackprotector.h>

@@ -95,7 +96,7 @@ static void __soft_restart(void *addr)
 	BUG();
 }
 
-void soft_restart(unsigned long addr)
+void _soft_restart(unsigned long addr, bool disable_l2)
 {
 	u64 *stack = soft_restart_stack + ARRAY_SIZE(soft_restart_stack);

@@ -104,7 +105,7 @@ void soft_restart(unsigned long addr)
 	local_fiq_disable();
 
 	/* Disable the L2 if we're the last man standing. */
-	if (num_online_cpus() == 1)
+	if (disable_l2)
 		outer_disable();
 
 	/* Change to the new stack and continue with the reset. */

@@ -114,6 +115,11 @@ void soft_restart(unsigned long addr)
 	BUG();
 }
 
+void soft_restart(unsigned long addr)
+{
+	_soft_restart(addr, num_online_cpus() == 1);
+}
+
 /*
  * Function pointers to optional machine specific functions
  */

arch/arm/kernel/reboot.h new file +6 -0

@@ -0,0 +1,6 @@
+#ifndef REBOOT_H
+#define REBOOT_H
+
+extern void _soft_restart(unsigned long addr, bool disable_l2);
+
+#endif

Patches currently in stable-queue which might be from [email protected] are

queue-3.19/arm-fix-broken-hibernation.patch queue-3.19/arm-8320-1-fix-integer-overflow-in-elf_et_dyn_base.patch