[PATCH v4 0/2] hibernation support on ARM

[PATCH v4 0/2] hibernation support on ARM

[Sebastian Capella]

Patches adding support for hibernation on ARM
 - ARM hibernation / suspend-to-disk
 - Change soft_restart to use non-tracing raw_local_irq_disable

Patches based on v3.13 tag, verified hibernation on beaglebone black on a
branch based on 3.13 merged with initial omap support from Russ Dill which
can be found here (includes v1 patchset):
http://git.linaro.org/git-ro/people/sebastian.capella/linux.git hibernation_3.13_russMerge

[PATCH v4 1/2] ARM: avoid tracers in soft_restart
 arch/arm/kernel/process.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

 Use raw_local_irq_disable in place of local_irq_disable to avoid
 infinite abort recursion while tracing. (unchanged since v3)

[PATCH v4 2/2] ARM hibernation / suspend-to-disk
 arch/arm/include/asm/memory.h |    1 +
 arch/arm/kernel/Makefile      |    1 +
 arch/arm/kernel/hibernate.c   |  113 +++++++++++++++++++++++++++++++++++++++++
 arch/arm/mm/Kconfig           |    5 ++
 include/linux/suspend.h       |    2 +
 5 files changed, 122 insertions(+)

 Adds support for ARM based hibernation


Additional notes:
-----------------

There are two checkpatch warnings added by this patch.  These follow
behavior in existing hibernation implementations on other platforms.

    WARNING: externs should be avoided in .c files
    #116: FILE: arch/arm/kernel/hibernate.c:26:
    +extern const void __nosave_begin, __nosave_end;

  This extern is picking up the linker nosave region definitions, only
  used in hibernate.  Follows same extern line used mips, powerpc, s390,
  sh, sparc, x86 & unicore32

    WARNING: externs should be avoided in .c files
    #191: FILE: arch/arm/kernel/hibernate.c:101:
    +extern void call_with_stack(void (*fn)(void *), void *arg, void *sp);

  This extern is used in the arch/arm/ in hibernate, process and bL_switcher


Changes in v4:
--------------
* updated comment for soft_restart with review feedback
* dropped freeze_processes patch which was queued separately 
  to 3.14 by Rafael Wysocki:
  https://lkml.org/lkml/2014/2/25/683

Changes in v3:
--------------
* added comment to use of soft_restart
* drop irq disable soft_restart patch
* add patch to avoid tracers in soft_restart by using raw_local_irq_*

Changes in v2:
--------------
* Removed unneeded flush_thread, use of __naked and cpu_init.
* dropped Cyril Chemparathy <cyril@ti.com> from Cc: list as 
  emails are bouncing.

Thanks,

Sebastian Capella

[PATCH v4 1/2] ARM: avoid tracers in soft_restart

[Sebastian Capella]

Use of tracers in local_irq_disable is causes recursive aborts when
called with irqs disabled and using a temporary stack (hibernation).
Replace local_irq_disable with raw_local_irq_disable instead to
avoid tracers.

Signed-off-by: Sebastian Capella <sebastian.capella@linaro.org>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Robin Holt <robin.m.holt@gmail.com>
Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
---
 arch/arm/kernel/process.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c
index 92f7b15..f58b723 100644
--- a/arch/arm/kernel/process.c
+++ b/arch/arm/kernel/process.c
@@ -100,7 +100,7 @@ void soft_restart(unsigned long addr)
 	u64 *stack = soft_restart_stack + ARRAY_SIZE(soft_restart_stack);
 
 	/* Disable interrupts first */
-	local_irq_disable();
+	raw_local_irq_disable();
 	local_fiq_disable();
 
 	/* Disable the L2 if we're the last man standing. */
-- 
1.7.9.5

Re: [PATCH v4 1/2] ARM: avoid tracers in soft_restart

[Russell King - ARM Linux]

On Wed, Feb 26, 2014 at 11:10:56AM -0800, Sebastian Capella wrote:
> Use of tracers in local_irq_disable is causes recursive aborts when
> called with irqs disabled and using a temporary stack (hibernation).
> Replace local_irq_disable with raw_local_irq_disable instead to
> avoid tracers.
> 
> Signed-off-by: Sebastian Capella <sebastian.capella@linaro.org>
> Cc: Russell King <linux@arm.linux.org.uk>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Will Deacon <will.deacon@arm.com>
> Cc: Robin Holt <robin.m.holt@gmail.com>
> Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
> ---
>  arch/arm/kernel/process.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c
> index 92f7b15..f58b723 100644
> --- a/arch/arm/kernel/process.c
> +++ b/arch/arm/kernel/process.c
> @@ -100,7 +100,7 @@ void soft_restart(unsigned long addr)
>  	u64 *stack = soft_restart_stack + ARRAY_SIZE(soft_restart_stack);
>  
>  	/* Disable interrupts first */
> -	local_irq_disable();
> +	raw_local_irq_disable();
>  	local_fiq_disable();

Great, I'm happy with this now.  I assume that the plan is to submit this
to my patch system when everyone's given their fill of acks?

-- 
FTTC broadband for 0.8mile line: now at 9.7Mbps down 460kbps up... slowly
improving, and getting towards what was expected from it.

Re: [PATCH v4 1/2] ARM: avoid tracers in soft_restart

[Sebastian Capella]

Quoting Russell King - ARM Linux (2014-02-26 15:37:44)
> On Wed, Feb 26, 2014 at 11:10:56AM -0800, Sebastian Capella wrote:
> > Use of tracers in local_irq_disable is causes recursive aborts when
> > called with irqs disabled and using a temporary stack (hibernation).
> > Replace local_irq_disable with raw_local_irq_disable instead to
> > avoid tracers.
> > 
> > Signed-off-by: Sebastian Capella <sebastian.capella@linaro.org>
> > Cc: Russell King <linux@arm.linux.org.uk>
> > Cc: Andrew Morton <akpm@linux-foundation.org>
> > Cc: Thomas Gleixner <tglx@linutronix.de>
> > Cc: Will Deacon <will.deacon@arm.com>
> > Cc: Robin Holt <robin.m.holt@gmail.com>
> > Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
> > ---
> >  arch/arm/kernel/process.c |    2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c
> > index 92f7b15..f58b723 100644
> > --- a/arch/arm/kernel/process.c
> > +++ b/arch/arm/kernel/process.c
> > @@ -100,7 +100,7 @@ void soft_restart(unsigned long addr)
> >       u64 *stack = soft_restart_stack + ARRAY_SIZE(soft_restart_stack);
> >  
> >       /* Disable interrupts first */
> > -     local_irq_disable();
> > +     raw_local_irq_disable();
> >       local_fiq_disable();
> 
> Great, I'm happy with this now.  I assume that the plan is to submit this
> to my patch system when everyone's given their fill of acks?

Thanks Russell!

I'll look into how to send it to your patch system and wait for people
to respond.

Sebastian Capella

[PATCH v4 2/2] ARM hibernation / suspend-to-disk

[Sebastian Capella]

From: Russ Dill <Russ.Dill@ti.com>

Enable hibernation for ARM architectures and provide ARM
architecture specific calls used during hibernation.

The swsusp hibernation framework depends on the
platform first having functional suspend/resume.

Then, in order to enable hibernation on a given platform, a
platform_hibernation_ops structure may need to be registered with
the system in order to save/restore any SoC-specific / cpu specific
state needing (re)init over a suspend-to-disk/resume-from-disk cycle.

For example:

     - "secure" SoCs that have different sets of control registers
       and/or different CR reg access patterns.

     - SoCs with L2 caches as the activation sequence there is
       SoC-dependent; a full off-on cycle for L2 is not done
       by the hibernation support code.

     - SoCs requiring steps on wakeup _before_ the "generic" parts
       done by cpu_suspend / cpu_resume can work correctly.

     - SoCs having persistent state which is maintained during suspend
       and resume, but will be lost during the power off cycle after
       suspend-to-disk.

This is a rebase/rework of Frank Hofmann's v5 hibernation patchset.

Cc: Russ Dill <Russ.Dill@ti.com>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Signed-off-by: Sebastian Capella <sebastian.capella@linaro.org>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Len Brown <len.brown@intel.com>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: Nicolas Pitre <nico@linaro.org>
Cc: Santosh Shilimkar <santosh.shilimkar@ti.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Jonathan Austin <jonathan.austin@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
Cc: Stephen Boyd <sboyd@codeaurora.org>
Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
---
 arch/arm/include/asm/memory.h |    1 +
 arch/arm/kernel/Makefile      |    1 +
 arch/arm/kernel/hibernate.c   |  113 +++++++++++++++++++++++++++++++++++++++++
 arch/arm/mm/Kconfig           |    5 ++
 include/linux/suspend.h       |    2 +
 5 files changed, 122 insertions(+)
 create mode 100644 arch/arm/kernel/hibernate.c

diff --git a/arch/arm/include/asm/memory.h b/arch/arm/include/asm/memory.h
index 8756e4b..1079ea8 100644
--- a/arch/arm/include/asm/memory.h
+++ b/arch/arm/include/asm/memory.h
@@ -291,6 +291,7 @@ static inline void *phys_to_virt(phys_addr_t x)
  */
 #define __pa(x)			__virt_to_phys((unsigned long)(x))
 #define __va(x)			((void *)__phys_to_virt((phys_addr_t)(x)))
+#define __pa_symbol(x)		__pa(RELOC_HIDE((unsigned long)(x), 0))
 #define pfn_to_kaddr(pfn)	__va((pfn) << PAGE_SHIFT)
 
 extern phys_addr_t (*arch_virt_to_idmap)(unsigned long x);
diff --git a/arch/arm/kernel/Makefile b/arch/arm/kernel/Makefile
index a30fc9b..8afa848 100644
--- a/arch/arm/kernel/Makefile
+++ b/arch/arm/kernel/Makefile
@@ -39,6 +39,7 @@ obj-$(CONFIG_ARTHUR)		+= arthur.o
 obj-$(CONFIG_ISA_DMA)		+= dma-isa.o
 obj-$(CONFIG_PCI)		+= bios32.o isa.o
 obj-$(CONFIG_ARM_CPU_SUSPEND)	+= sleep.o suspend.o
+obj-$(CONFIG_HIBERNATION)	+= hibernate.o
 obj-$(CONFIG_SMP)		+= smp.o
 ifdef CONFIG_MMU
 obj-$(CONFIG_SMP)		+= smp_tlb.o
diff --git a/arch/arm/kernel/hibernate.c b/arch/arm/kernel/hibernate.c
new file mode 100644
index 0000000..70e17d2
--- /dev/null
+++ b/arch/arm/kernel/hibernate.c
@@ -0,0 +1,113 @@
+/*
+ * Hibernation support specific for ARM
+ *
+ * Derived from work on ARM hibernation support by:
+ *
+ * Ubuntu project, hibernation support for mach-dove
+ * Copyright (C) 2010 Nokia Corporation (Hiroshi Doyu)
+ * Copyright (C) 2010 Texas Instruments, Inc. (Teerth Reddy et al.)
+ *  https://lkml.org/lkml/2010/6/18/4
+ *  https://lists.linux-foundation.org/pipermail/linux-pm/2010-June/027422.html
+ *  https://patchwork.kernel.org/patch/96442/
+ *
+ * Copyright (C) 2006 Rafael J. Wysocki <rjw@sisk.pl>
+ *
+ * License terms: GNU General Public License (GPL) version 2
+ */
+
+#include <linux/mm.h>
+#include <linux/suspend.h>
+#include <asm/tlbflush.h>
+#include <asm/cacheflush.h>
+#include <asm/system_misc.h>
+#include <asm/idmap.h>
+#include <asm/suspend.h>
+
+extern const void __nosave_begin, __nosave_end;
+
+int pfn_is_nosave(unsigned long pfn)
+{
+	unsigned long nosave_begin_pfn =
+			__pa_symbol(&__nosave_begin) >> PAGE_SHIFT;
+	unsigned long nosave_end_pfn =
+			PAGE_ALIGN(__pa_symbol(&__nosave_end)) >> PAGE_SHIFT;
+
+	return (pfn >= nosave_begin_pfn) && (pfn < nosave_end_pfn);
+}
+
+void notrace save_processor_state(void)
+{
+	WARN_ON(num_online_cpus() != 1);
+	local_fiq_disable();
+}
+
+void notrace restore_processor_state(void)
+{
+	local_fiq_enable();
+}
+
+/*
+ * Snapshot kernel memory and reset the system.
+ *
+ * swsusp_save() is executed in the suspend finisher so that the CPU
+ * context pointer and memory are part of the saved image, which is
+ * required by the resume kernel image to restart execution from
+ * swsusp_arch_suspend().
+ *
+ * soft_restart is not technically needed, but is used to get success
+ * returned from cpu_suspend.
+ * 
+ * When soft reboot completes, the hibernation snapshot is written out.
+ */
+static int notrace __swsusp_arch_save_image(unsigned long unused)
+{
+	int ret;
+
+	ret = swsusp_save();
+	if (ret == 0)
+		soft_restart(virt_to_phys(cpu_resume));
+	return ret;
+}
+
+/*
+ * Save the current CPU state before suspend / poweroff.
+ */
+int notrace swsusp_arch_suspend(void)
+{
+	return cpu_suspend(0, __swsusp_arch_save_image);
+}
+
+/*
+ * The framework loads the hibernation image into a linked list anchored
+ * at restore_pblist, for swsusp_arch_resume() to copy back to the proper
+ * destinations.
+ *
+ * To make this work if resume is triggered from initramfs, the
+ * pagetables need to be switched to allow writes to kernel mem.
+ */
+static void notrace __swsusp_arch_restore_image(void *unused)
+{
+	struct pbe *pbe;
+
+	cpu_switch_mm(idmap_pgd, &init_mm);
+	for (pbe = restore_pblist; pbe; pbe = pbe->next)
+		copy_page(pbe->orig_address, pbe->address);
+
+	soft_restart(virt_to_phys(cpu_resume));
+}
+
+static u8 __swsusp_resume_stk[PAGE_SIZE/2] __nosavedata;
+
+/*
+ * Resume from the hibernation image.
+ * Due to the kernel heap / data restore, stack contents change underneath
+ * and that would make function calls impossible; switch to a temporary
+ * stack within the nosave region to avoid that problem.
+ */
+int swsusp_arch_resume(void)
+{
+	extern void call_with_stack(void (*fn)(void *), void *arg, void *sp);
+	call_with_stack(__swsusp_arch_restore_image, 0,
+		__swsusp_resume_stk + sizeof(__swsusp_resume_stk));
+	return 0;
+}
diff --git a/arch/arm/mm/Kconfig b/arch/arm/mm/Kconfig
index 1f8fed9..83707702 100644
--- a/arch/arm/mm/Kconfig
+++ b/arch/arm/mm/Kconfig
@@ -611,6 +611,11 @@ config CPU_USE_DOMAINS
 config IO_36
 	bool
 
+config ARCH_HIBERNATION_POSSIBLE
+	bool
+	depends on MMU
+	default y if CPU_ARM920T || CPU_ARM926T || CPU_SA1100 || CPU_XSCALE || CPU_XSC3 || CPU_V6 || CPU_V6K || CPU_V7
+
 comment "Processor Features"
 
 config ARM_LPAE
diff --git a/include/linux/suspend.h b/include/linux/suspend.h
index f73cabf..38bbf95 100644
--- a/include/linux/suspend.h
+++ b/include/linux/suspend.h
@@ -320,6 +320,8 @@ extern unsigned long get_safe_page(gfp_t gfp_mask);
 extern void hibernation_set_ops(const struct platform_hibernation_ops *ops);
 extern int hibernate(void);
 extern bool system_entering_hibernation(void);
+asmlinkage int swsusp_save(void);
+extern struct pbe *restore_pblist;
 #else /* CONFIG_HIBERNATION */
 static inline void register_nosave_region(unsigned long b, unsigned long e) {}
 static inline void register_nosave_region_late(unsigned long b, unsigned long e) {}
-- 
1.7.9.5

Re: [PATCH v4 2/2] ARM hibernation / suspend-to-disk

[Russ Dill]

On 02/26/2014 11:10 AM, Sebastian Capella wrote:
> From: Russ Dill <Russ.Dill@ti.com>
> 
> Enable hibernation for ARM architectures and provide ARM
> architecture specific calls used during hibernation.
> 
> The swsusp hibernation framework depends on the
> platform first having functional suspend/resume.
> 
> Then, in order to enable hibernation on a given platform, a
> platform_hibernation_ops structure may need to be registered with
> the system in order to save/restore any SoC-specific / cpu specific
> state needing (re)init over a suspend-to-disk/resume-from-disk cycle.
> 
> For example:
> 
>      - "secure" SoCs that have different sets of control registers
>        and/or different CR reg access patterns.
> 
>      - SoCs with L2 caches as the activation sequence there is
>        SoC-dependent; a full off-on cycle for L2 is not done
>        by the hibernation support code.
> 
>      - SoCs requiring steps on wakeup _before_ the "generic" parts
>        done by cpu_suspend / cpu_resume can work correctly.
> 
>      - SoCs having persistent state which is maintained during suspend
>        and resume, but will be lost during the power off cycle after
>        suspend-to-disk.
> 
> This is a rebase/rework of Frank Hofmann's v5 hibernation patchset.
> 
> Cc: Russ Dill <Russ.Dill@ti.com>
> Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
> Signed-off-by: Sebastian Capella <sebastian.capella@linaro.org>
> Cc: Russell King <linux@arm.linux.org.uk>
> Cc: Len Brown <len.brown@intel.com>
> Cc: Pavel Machek <pavel@ucw.cz>
> Cc: Nicolas Pitre <nico@linaro.org>
> Cc: Santosh Shilimkar <santosh.shilimkar@ti.com>
> Cc: Will Deacon <will.deacon@arm.com>
> Cc: Jonathan Austin <jonathan.austin@arm.com>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
> Cc: Stephen Boyd <sboyd@codeaurora.org>
> Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>

Acked-by: Russ Dill <russ.dill@ti.com>


> ---
>  arch/arm/include/asm/memory.h |    1 +
>  arch/arm/kernel/Makefile      |    1 +
>  arch/arm/kernel/hibernate.c   |  113 +++++++++++++++++++++++++++++++++++++++++
>  arch/arm/mm/Kconfig           |    5 ++
>  include/linux/suspend.h       |    2 +
>  5 files changed, 122 insertions(+)
>  create mode 100644 arch/arm/kernel/hibernate.c
> 
> diff --git a/arch/arm/include/asm/memory.h b/arch/arm/include/asm/memory.h
> index 8756e4b..1079ea8 100644
> --- a/arch/arm/include/asm/memory.h
> +++ b/arch/arm/include/asm/memory.h
> @@ -291,6 +291,7 @@ static inline void *phys_to_virt(phys_addr_t x)
>   */
>  #define __pa(x)			__virt_to_phys((unsigned long)(x))
>  #define __va(x)			((void *)__phys_to_virt((phys_addr_t)(x)))
> +#define __pa_symbol(x)		__pa(RELOC_HIDE((unsigned long)(x), 0))
>  #define pfn_to_kaddr(pfn)	__va((pfn) << PAGE_SHIFT)
>  
>  extern phys_addr_t (*arch_virt_to_idmap)(unsigned long x);
> diff --git a/arch/arm/kernel/Makefile b/arch/arm/kernel/Makefile
> index a30fc9b..8afa848 100644
> --- a/arch/arm/kernel/Makefile
> +++ b/arch/arm/kernel/Makefile
> @@ -39,6 +39,7 @@ obj-$(CONFIG_ARTHUR)		+= arthur.o
>  obj-$(CONFIG_ISA_DMA)		+= dma-isa.o
>  obj-$(CONFIG_PCI)		+= bios32.o isa.o
>  obj-$(CONFIG_ARM_CPU_SUSPEND)	+= sleep.o suspend.o
> +obj-$(CONFIG_HIBERNATION)	+= hibernate.o
>  obj-$(CONFIG_SMP)		+= smp.o
>  ifdef CONFIG_MMU
>  obj-$(CONFIG_SMP)		+= smp_tlb.o
> diff --git a/arch/arm/kernel/hibernate.c b/arch/arm/kernel/hibernate.c
> new file mode 100644
> index 0000000..70e17d2
> --- /dev/null
> +++ b/arch/arm/kernel/hibernate.c
> @@ -0,0 +1,113 @@
> +/*
> + * Hibernation support specific for ARM
> + *
> + * Derived from work on ARM hibernation support by:
> + *
> + * Ubuntu project, hibernation support for mach-dove
> + * Copyright (C) 2010 Nokia Corporation (Hiroshi Doyu)
> + * Copyright (C) 2010 Texas Instruments, Inc. (Teerth Reddy et al.)
> + *  https://lkml.org/lkml/2010/6/18/4
> + *  https://lists.linux-foundation.org/pipermail/linux-pm/2010-June/027422.html
> + *  https://patchwork.kernel.org/patch/96442/
> + *
> + * Copyright (C) 2006 Rafael J. Wysocki <rjw@sisk.pl>
> + *
> + * License terms: GNU General Public License (GPL) version 2
> + */
> +
> +#include <linux/mm.h>
> +#include <linux/suspend.h>
> +#include <asm/tlbflush.h>
> +#include <asm/cacheflush.h>
> +#include <asm/system_misc.h>
> +#include <asm/idmap.h>
> +#include <asm/suspend.h>
> +
> +extern const void __nosave_begin, __nosave_end;
> +
> +int pfn_is_nosave(unsigned long pfn)
> +{
> +	unsigned long nosave_begin_pfn =
> +			__pa_symbol(&__nosave_begin) >> PAGE_SHIFT;
> +	unsigned long nosave_end_pfn =
> +			PAGE_ALIGN(__pa_symbol(&__nosave_end)) >> PAGE_SHIFT;
> +
> +	return (pfn >= nosave_begin_pfn) && (pfn < nosave_end_pfn);
> +}
> +
> +void notrace save_processor_state(void)
> +{
> +	WARN_ON(num_online_cpus() != 1);
> +	local_fiq_disable();
> +}
> +
> +void notrace restore_processor_state(void)
> +{
> +	local_fiq_enable();
> +}
> +
> +/*
> + * Snapshot kernel memory and reset the system.
> + *
> + * swsusp_save() is executed in the suspend finisher so that the CPU
> + * context pointer and memory are part of the saved image, which is
> + * required by the resume kernel image to restart execution from
> + * swsusp_arch_suspend().
> + *
> + * soft_restart is not technically needed, but is used to get success
> + * returned from cpu_suspend.
> + * 
> + * When soft reboot completes, the hibernation snapshot is written out.
> + */
> +static int notrace __swsusp_arch_save_image(unsigned long unused)
> +{
> +	int ret;
> +
> +	ret = swsusp_save();
> +	if (ret == 0)
> +		soft_restart(virt_to_phys(cpu_resume));
> +	return ret;
> +}
> +
> +/*
> + * Save the current CPU state before suspend / poweroff.
> + */
> +int notrace swsusp_arch_suspend(void)
> +{
> +	return cpu_suspend(0, __swsusp_arch_save_image);
> +}
> +
> +/*
> + * The framework loads the hibernation image into a linked list anchored
> + * at restore_pblist, for swsusp_arch_resume() to copy back to the proper
> + * destinations.
> + *
> + * To make this work if resume is triggered from initramfs, the
> + * pagetables need to be switched to allow writes to kernel mem.
> + */
> +static void notrace __swsusp_arch_restore_image(void *unused)
> +{
> +	struct pbe *pbe;
> +
> +	cpu_switch_mm(idmap_pgd, &init_mm);
> +	for (pbe = restore_pblist; pbe; pbe = pbe->next)
> +		copy_page(pbe->orig_address, pbe->address);
> +
> +	soft_restart(virt_to_phys(cpu_resume));
> +}
> +
> +static u8 __swsusp_resume_stk[PAGE_SIZE/2] __nosavedata;
> +
> +/*
> + * Resume from the hibernation image.
> + * Due to the kernel heap / data restore, stack contents change underneath
> + * and that would make function calls impossible; switch to a temporary
> + * stack within the nosave region to avoid that problem.
> + */
> +int swsusp_arch_resume(void)
> +{
> +	extern void call_with_stack(void (*fn)(void *), void *arg, void *sp);
> +	call_with_stack(__swsusp_arch_restore_image, 0,
> +		__swsusp_resume_stk + sizeof(__swsusp_resume_stk));
> +	return 0;
> +}
> diff --git a/arch/arm/mm/Kconfig b/arch/arm/mm/Kconfig
> index 1f8fed9..83707702 100644
> --- a/arch/arm/mm/Kconfig
> +++ b/arch/arm/mm/Kconfig
> @@ -611,6 +611,11 @@ config CPU_USE_DOMAINS
>  config IO_36
>  	bool
>  
> +config ARCH_HIBERNATION_POSSIBLE
> +	bool
> +	depends on MMU
> +	default y if CPU_ARM920T || CPU_ARM926T || CPU_SA1100 || CPU_XSCALE || CPU_XSC3 || CPU_V6 || CPU_V6K || CPU_V7
> +
>  comment "Processor Features"
>  
>  config ARM_LPAE
> diff --git a/include/linux/suspend.h b/include/linux/suspend.h
> index f73cabf..38bbf95 100644
> --- a/include/linux/suspend.h
> +++ b/include/linux/suspend.h
> @@ -320,6 +320,8 @@ extern unsigned long get_safe_page(gfp_t gfp_mask);
>  extern void hibernation_set_ops(const struct platform_hibernation_ops *ops);
>  extern int hibernate(void);
>  extern bool system_entering_hibernation(void);
> +asmlinkage int swsusp_save(void);
> +extern struct pbe *restore_pblist;
>  #else /* CONFIG_HIBERNATION */
>  static inline void register_nosave_region(unsigned long b, unsigned long e) {}
>  static inline void register_nosave_region_late(unsigned long b, unsigned long e) {}
> 


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