[3.16.y-ckt stable] Patch "ARM: fix broken hibernation" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    ARM: fix broken hibernation

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt11.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 5f901a51dd5b2f7ce35310e7e1610c393935e26c Mon Sep 17 00:00:00 2001
From: Russell King <rmk+kernel at arm.linux.org.uk>
Date: Wed, 1 Apr 2015 16:20:39 +0100
Subject: ARM: fix broken hibernation

commit 767bf7e7a1e82a81c59778348d156993d0a6175d upstream.

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 <xobs at kosagi.com>
Tested-by: Sean Cross <xobs at kosagi.com>
Signed-off-by: Russell King <rmk+kernel at arm.linux.org.uk>
[ luis: backported to 3.16: adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 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(-)
 create mode 100644 arch/arm/kernel/reboot.h

diff --git a/arch/arm/kernel/hibernate.c b/arch/arm/kernel/hibernate.c
index c4cc50e58c13..cfb354ff2a60 100644
--- a/arch/arm/kernel/hibernate.c
+++ b/arch/arm/kernel/hibernate.c
@@ -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(unsigned long unused)

 	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(void *unused)
 	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;
diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c
index a35f6ebbd2c2..3f688b73dda2 100644
--- a/arch/arm/kernel/process.c
+++ b/arch/arm/kernel/process.c
@@ -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. */
@@ -118,6 +119,11 @@ static void null_restart(enum reboot_mode reboot_mode, const char *cmd)
 {
 }

+void soft_restart(unsigned long addr)
+{
+	_soft_restart(addr, num_online_cpus() == 1);
+}
+
 /*
  * Function pointers to optional machine specific functions
  */
diff --git a/arch/arm/kernel/reboot.h b/arch/arm/kernel/reboot.h
new file mode 100644
index 000000000000..c87f05816d6b
--- /dev/null
+++ b/arch/arm/kernel/reboot.h
@@ -0,0 +1,6 @@
+#ifndef REBOOT_H
+#define REBOOT_H
+
+extern void _soft_restart(unsigned long addr, bool disable_l2);
+
+#endif