[PATCH v2 3/3] RISC-V: Add arch functions to support hibernation/suspend-to-disk

[Sia Jee Heng]

Low level Arch functions were created to support hibernation.
swsusp_arch_suspend() relies code from __cpu_suspend_enter() to write
cpu state onto the stack, then calling swsusp_save() to save the memory
image.

arch_hibernation_header_restore() and arch_hibernation_header_save()
functions are implemented to prevent kernel crash when resume,
the kernel built version is saved into the hibernation image header
to making sure only the same kernel is restore when resume.

swsusp_arch_resume() creates a temporary page table that covering only
the linear map, copies the restore code to a 'safe' page, then start to
restore the memory image. Once completed, it restores the original
kernel's page table. It then calls into __hibernate_cpu_resume()
to restore the CPU context. Finally, it follows the normal hibernation
path back to the hibernation core.

To enable hibernation/suspend to disk into RISCV, the below config
need to be enabled:
- CONFIG_ARCH_HIBERNATION_HEADER
- CONFIG_ARCH_HIBERNATION_POSSIBLE
- CONFIG_ARCH_RV64I
- CONFIG_64BIT

Signed-off-by: Sia Jee Heng <jeeheng.sia@xxxxxxxxxxxxxxxx>
Reviewed-by: Ley Foon Tan <leyfoon.tan@xxxxxxxxxxxxxxxx>
Reviewed-by: Mason Huo <mason.huo@xxxxxxxxxxxxxxxx>
---
 arch/riscv/Kconfig                |   8 +
 arch/riscv/include/asm/suspend.h  |  20 ++
 arch/riscv/kernel/Makefile        |   2 +-
 arch/riscv/kernel/asm-offsets.c   |   5 +
 arch/riscv/kernel/hibernate-asm.S | 123 +++++++++++
 arch/riscv/kernel/hibernate.c     | 353 ++++++++++++++++++++++++++++++
 6 files changed, 510 insertions(+), 1 deletion(-)
 create mode 100644 arch/riscv/kernel/hibernate-asm.S
 create mode 100644 arch/riscv/kernel/hibernate.c

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index e2b656043abf..3c2607b6bda7 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -690,6 +690,14 @@ menu "Power management options"
 
 source "kernel/power/Kconfig"
 
+config ARCH_HIBERNATION_POSSIBLE
+	def_bool y
+	depends on 64BIT
+
+config ARCH_HIBERNATION_HEADER
+	def_bool y
+	depends on HIBERNATION && 64BIT
+
 endmenu # "Power management options"
 
 menu "CPU Power Management"
diff --git a/arch/riscv/include/asm/suspend.h b/arch/riscv/include/asm/suspend.h
index 75419c5ca272..ebaf103aec40 100644
--- a/arch/riscv/include/asm/suspend.h
+++ b/arch/riscv/include/asm/suspend.h
@@ -21,6 +21,11 @@ struct suspend_context {
 #endif
 };
 
+/* This parameter will be assigned to 0 during resume and will be used by
+ * hibernation core for the subsequent resume sequence
+ */
+extern int in_suspend;
+
 /* Low-level CPU suspend entry function */
 int __cpu_suspend_enter(struct suspend_context *context);
 
@@ -36,4 +41,19 @@ int __cpu_resume_enter(unsigned long hartid, unsigned long context);
 /* Used to save and restore the csr */
 void suspend_save_csrs(struct suspend_context *context);
 void suspend_restore_csrs(struct suspend_context *context);
+
+/* Low-level API to support hibernation */
+int swsusp_arch_suspend(void);
+int swsusp_arch_resume(void);
+int arch_hibernation_header_save(void *addr, unsigned int max_size);
+int arch_hibernation_header_restore(void *addr);
+int __hibernate_cpu_resume(void);
+
+/* Used to resume on the CPU we hibernated on */
+int hibernate_resume_nonboot_cpu_disable(void);
+
+/* Used to restore the hibernated image */
+asmlinkage void restore_image(unsigned long resume_satp, unsigned long satp_temp,
+				unsigned long cpu_resume);
+asmlinkage int core_restore_code(void);
 #endif
diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
index 4cf303a779ab..df83b8cea631 100644
--- a/arch/riscv/kernel/Makefile
+++ b/arch/riscv/kernel/Makefile
@@ -64,7 +64,7 @@ obj-$(CONFIG_MODULES)		+= module.o
 obj-$(CONFIG_MODULE_SECTIONS)	+= module-sections.o
 
 obj-$(CONFIG_CPU_PM)		+= suspend_entry.o suspend.o
-
+obj-$(CONFIG_HIBERNATION)	+= hibernate.o hibernate-asm.o
 obj-$(CONFIG_FUNCTION_TRACER)	+= mcount.o ftrace.o
 obj-$(CONFIG_DYNAMIC_FTRACE)	+= mcount-dyn.o
 
diff --git a/arch/riscv/kernel/asm-offsets.c b/arch/riscv/kernel/asm-offsets.c
index df9444397908..d6a75aac1d27 100644
--- a/arch/riscv/kernel/asm-offsets.c
+++ b/arch/riscv/kernel/asm-offsets.c
@@ -9,6 +9,7 @@
 #include <linux/kbuild.h>
 #include <linux/mm.h>
 #include <linux/sched.h>
+#include <linux/suspend.h>
 #include <asm/kvm_host.h>
 #include <asm/thread_info.h>
 #include <asm/ptrace.h>
@@ -116,6 +117,10 @@ void asm_offsets(void)
 
 	OFFSET(SUSPEND_CONTEXT_REGS, suspend_context, regs);
 
+	OFFSET(HIBERN_PBE_ADDR, pbe, address);
+	OFFSET(HIBERN_PBE_ORIG, pbe, orig_address);
+	OFFSET(HIBERN_PBE_NEXT, pbe, next);
+
 	OFFSET(KVM_ARCH_GUEST_ZERO, kvm_vcpu_arch, guest_context.zero);
 	OFFSET(KVM_ARCH_GUEST_RA, kvm_vcpu_arch, guest_context.ra);
 	OFFSET(KVM_ARCH_GUEST_SP, kvm_vcpu_arch, guest_context.sp);
diff --git a/arch/riscv/kernel/hibernate-asm.S b/arch/riscv/kernel/hibernate-asm.S
new file mode 100644
index 000000000000..81d9dc98d0ad
--- /dev/null
+++ b/arch/riscv/kernel/hibernate-asm.S
@@ -0,0 +1,123 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Hibernation support specific for RISCV
+ *
+ * Copyright (C) 2023 StarFive Technology Co., Ltd.
+ *
+ * Author: Jee Heng Sia <jeeheng.sia@xxxxxxxxxxxxxxxx>
+ */
+
+#include <asm/asm.h>
+#include <asm/asm-offsets.h>
+#include <asm/csr.h>
+#include <linux/linkage.h>
+
+/*
+ * These code are to be executed when resume from the hibernation.
+ *
+ * It begins with loads the temporary page table then restores the memory image.
+ * Finally branches to __hibernate_cpu_resume() to restore the state saved by
+ * swsusp_arch_suspend().
+ */
+
+/*
+ * int __hibernate_cpu_resume(void)
+ * Switch back to the hibernated image's page table prior to restore the CPU
+ * context.
+ *
+ * Always returns 0 to the C code.
+ */
+ENTRY(__hibernate_cpu_resume)
+        /* switch to hibernated image's page table */
+        csrw CSR_SATP, s0
+        sfence.vma
+
+	ld	a0, hibernate_cpu_context
+
+	/* Restore CSRs */
+	REG_L   t0, (SUSPEND_CONTEXT_REGS + PT_EPC)(a0)
+	csrw    CSR_EPC, t0
+	REG_L   t0, (SUSPEND_CONTEXT_REGS + PT_STATUS)(a0)
+	csrw    CSR_STATUS, t0
+	REG_L   t0, (SUSPEND_CONTEXT_REGS + PT_BADADDR)(a0)
+	csrw    CSR_TVAL, t0
+	REG_L   t0, (SUSPEND_CONTEXT_REGS + PT_CAUSE)(a0)
+	csrw    CSR_CAUSE, t0
+
+	/* Restore registers (except A0 and T0-T6) */
+	REG_L   ra, (SUSPEND_CONTEXT_REGS + PT_RA)(a0)
+	REG_L   sp, (SUSPEND_CONTEXT_REGS + PT_SP)(a0)
+	REG_L   gp, (SUSPEND_CONTEXT_REGS + PT_GP)(a0)
+	REG_L   tp, (SUSPEND_CONTEXT_REGS + PT_TP)(a0)
+
+	REG_L   s0, (SUSPEND_CONTEXT_REGS + PT_S0)(a0)
+	REG_L   s1, (SUSPEND_CONTEXT_REGS + PT_S1)(a0)
+	REG_L   a1, (SUSPEND_CONTEXT_REGS + PT_A1)(a0)
+	REG_L   a2, (SUSPEND_CONTEXT_REGS + PT_A2)(a0)
+	REG_L   a3, (SUSPEND_CONTEXT_REGS + PT_A3)(a0)
+	REG_L   a4, (SUSPEND_CONTEXT_REGS + PT_A4)(a0)
+	REG_L   a5, (SUSPEND_CONTEXT_REGS + PT_A5)(a0)
+	REG_L   a6, (SUSPEND_CONTEXT_REGS + PT_A6)(a0)
+	REG_L   a7, (SUSPEND_CONTEXT_REGS + PT_A7)(a0)
+	REG_L   s2, (SUSPEND_CONTEXT_REGS + PT_S2)(a0)
+	REG_L   s3, (SUSPEND_CONTEXT_REGS + PT_S3)(a0)
+	REG_L   s4, (SUSPEND_CONTEXT_REGS + PT_S4)(a0)
+	REG_L   s5, (SUSPEND_CONTEXT_REGS + PT_S5)(a0)
+	REG_L   s6, (SUSPEND_CONTEXT_REGS + PT_S6)(a0)
+	REG_L   s7, (SUSPEND_CONTEXT_REGS + PT_S7)(a0)
+	REG_L   s8, (SUSPEND_CONTEXT_REGS + PT_S8)(a0)
+	REG_L   s9, (SUSPEND_CONTEXT_REGS + PT_S9)(a0)
+	REG_L   s10, (SUSPEND_CONTEXT_REGS + PT_S10)(a0)
+	REG_L   s11, (SUSPEND_CONTEXT_REGS + PT_S11)(a0)
+
+	/* Return zero value */
+	add     a0, zero, zero
+
+	ret
+END(__hibernate_cpu_resume)
+
+/*
+ * Prepare to restore the image.
+ * a0: satp of saved page tables
+ * a1: satp of temporary page tables
+ * a2: cpu_resume
+ */
+ENTRY(restore_image)
+	mv	s0, a0
+	mv	s1, a1
+	mv	s2, a2
+	ld      s4, restore_pblist
+	ld	a1, relocated_restore_code
+
+	jalr	a1
+END(restore_image)
+
+/*
+ * The below code will be executed from a 'safe' page.
+ * It first switches to the temporary page table, then start to copy the pages
+ * back to the original memory location. Finally, it jumps to the __hibernate_cpu_resume()
+ * to restore the CPU context.
+ */
+ENTRY(core_restore_code)
+	/* switch to temp page table */
+	csrw satp, s1
+	sfence.vma
+	beqz	s4, done
+loop:
+	/* The below code will restore the hibernated image. */
+	ld	a1, HIBERN_PBE_ADDR(s4)
+	ld	a0, HIBERN_PBE_ORIG(s4)
+
+	lui     a4, 0x1
+	add     a4, a4, a0
+copy:	ld      a5, 0(a1)
+	addi    a0, a0, 8
+	addi    a1, a1, 8
+	sd      a5, -8(a0)
+	bne     a4, a0, copy
+
+	ld	s4, HIBERN_PBE_NEXT(s4)
+	bnez	s4, loop
+done:
+	jalr	s2
+END(core_restore_code)
diff --git a/arch/riscv/kernel/hibernate.c b/arch/riscv/kernel/hibernate.c
new file mode 100644
index 000000000000..bd77c35958a8
--- /dev/null
+++ b/arch/riscv/kernel/hibernate.c
@@ -0,0 +1,353 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Hibernation support specific for RISCV
+ *
+ * Copyright (C) 2023 StarFive Technology Co., Ltd.
+ *
+ * Author: Jee Heng Sia <jeeheng.sia@xxxxxxxxxxxxxxxx>
+ */
+
+#include <asm/barrier.h>
+#include <asm/cacheflush.h>
+#include <asm/mmu_context.h>
+#include <asm/page.h>
+#include <asm/pgtable.h>
+#include <asm/sections.h>
+#include <asm/set_memory.h>
+#include <asm/smp.h>
+#include <asm/suspend.h>
+
+#include <linux/cpu.h>
+#include <linux/memblock.h>
+#include <linux/pm.h>
+#include <linux/sched.h>
+#include <linux/suspend.h>
+#include <linux/utsname.h>
+
+/*
+ * The logical cpu number we should resume on, initialised to a non-cpu
+ * number.
+ */
+static int sleep_cpu = -EINVAL;
+
+/* CPU context to be saved */
+struct suspend_context *hibernate_cpu_context;
+
+unsigned long relocated_restore_code;
+
+/* Pointer to the temporary resume page tables */
+pgd_t *resume_pg_dir;
+
+/*
+ * Save the build number and date so that the we are not resume with a different kernel
+ */
+struct arch_hibernate_hdr_invariants {
+	char		uts_version[__NEW_UTS_LEN + 1];
+};
+
+/* Helper parameters that help us to restore the image.
+ * @hartid: To make sure same boot_cpu executing the hibernate/restore code.
+ * @saved_satp: Original page table used by the hibernated image.
+ * @restore_cpu_addr: The kernel's image address to restore the CPU context.
+ */
+static struct arch_hibernate_hdr {
+	struct arch_hibernate_hdr_invariants invariants;
+	unsigned long	hartid;
+	unsigned long	saved_satp;
+	unsigned long	restore_cpu_addr;
+} resume_hdr;
+
+static inline void arch_hdr_invariants(struct arch_hibernate_hdr_invariants *i)
+{
+	memset(i, 0, sizeof(*i));
+	memcpy(i->uts_version, init_utsname()->version, sizeof(i->uts_version));
+}
+
+/*
+ * Check if the given pfn is in the 'nosave' section.
+ */
+int pfn_is_nosave(unsigned long pfn)
+{
+	unsigned long nosave_begin_pfn = sym_to_pfn(&__nosave_begin);
+	unsigned long nosave_end_pfn = sym_to_pfn(&__nosave_end - 1);
+
+	return ((pfn >= nosave_begin_pfn) && (pfn <= nosave_end_pfn));
+}
+
+void notrace save_processor_state(void)
+{
+	WARN_ON(num_online_cpus() != 1);
+}
+
+void notrace restore_processor_state(void)
+{
+}
+
+/*
+ * Helper parameters need to be saved to the hibernation image header.
+ */
+int arch_hibernation_header_save(void *addr, unsigned int max_size)
+{
+	struct arch_hibernate_hdr *hdr = addr;
+
+	if (max_size < sizeof(*hdr))
+		return -EOVERFLOW;
+
+	arch_hdr_invariants(&hdr->invariants);
+
+	hdr->hartid = cpuid_to_hartid_map(sleep_cpu);
+	hdr->saved_satp = csr_read(CSR_SATP);
+	hdr->restore_cpu_addr = (unsigned long) __hibernate_cpu_resume;
+
+	return 0;
+}
+EXPORT_SYMBOL(arch_hibernation_header_save);
+
+/*
+ * Retrieve the helper parameters from the hibernation image header
+ */
+int arch_hibernation_header_restore(void *addr)
+{
+	struct arch_hibernate_hdr_invariants invariants;
+	struct arch_hibernate_hdr *hdr = addr;
+	int ret = 0;
+
+	arch_hdr_invariants(&invariants);
+
+	if (memcmp(&hdr->invariants, &invariants, sizeof(invariants))) {
+		pr_crit("Hibernate image not generated by this kernel!\n");
+		return -EINVAL;
+	}
+
+	sleep_cpu = riscv_hartid_to_cpuid(hdr->hartid);
+	if (sleep_cpu < 0) {
+		pr_crit("Hibernated on a CPU not known to this kernel!\n");
+		sleep_cpu = -EINVAL;
+		return -EINVAL;
+	}
+
+#ifdef CONFIG_SMP
+	ret = bringup_hibernate_cpu(sleep_cpu);
+	if (ret) {
+		sleep_cpu = -EINVAL;
+		return ret;
+	}
+#endif
+	resume_hdr = *hdr;
+
+	return ret;
+}
+EXPORT_SYMBOL(arch_hibernation_header_restore);
+
+int swsusp_arch_suspend(void)
+{
+	int ret = 0;
+
+	if (__cpu_suspend_enter(hibernate_cpu_context)) {
+		sleep_cpu = smp_processor_id();
+		suspend_save_csrs(hibernate_cpu_context);
+		ret = swsusp_save();
+	} else {
+		suspend_restore_csrs(hibernate_cpu_context);
+		flush_tlb_all();
+
+		/* Invalidated Icache */
+		flush_icache_all();
+
+		/*
+		 * Tell the hibernation core that we've just restored
+		 * the memory
+		 */
+		in_suspend = 0;
+		sleep_cpu = -EINVAL;
+	}
+
+	return ret;
+}
+
+#define temp_pgtable_map_pgd_next(pgdp, vaddr, prot)			\
+		(pgtable_l5_enabled ?					\
+		temp_pgtable_map_p4d(pgdp, vaddr, prot) :		\
+		(pgtable_l4_enabled ?					\
+		temp_pgtable_map_pud((pud_t *)pgdp, vaddr, prot) :	\
+		temp_pgtable_map_pmd((pmd_t *)pgdp, vaddr, prot)))
+
+static unsigned long temp_pgtable_map_pte(pte_t *ptep, unsigned long vaddr, pgprot_t prot)
+{
+	uintptr_t pte_idx = pte_index(vaddr);
+
+	ptep[pte_idx] = pfn_pte(PFN_DOWN(__pa(vaddr)), prot);
+
+	return 0;
+}
+
+static unsigned long temp_pgtable_map_pmd(pmd_t *pmdp, unsigned long vaddr, pgprot_t prot)
+{
+	uintptr_t pmd_idx = pmd_index(vaddr);
+	pte_t *ptep;
+
+	if (pmd_none(pmdp[pmd_idx])) {
+		ptep = (pte_t *) get_safe_page(GFP_ATOMIC);
+		if (!ptep)
+			return -ENOMEM;
+
+		memset(ptep, 0, PAGE_SIZE);
+		pmdp[pmd_idx] = pfn_pmd(PFN_DOWN(__pa(ptep)), PAGE_TABLE);
+	} else {
+		ptep = (pte_t *) __va(PFN_PHYS(_pmd_pfn(pmdp[pmd_idx])));
+	}
+
+	return temp_pgtable_map_pte(ptep, vaddr, prot);
+}
+
+static unsigned long temp_pgtable_map_pud(pud_t *pudp, unsigned long vaddr, pgprot_t prot)
+{
+
+	uintptr_t pud_index = pud_index(vaddr);
+	pmd_t *pmdp;
+
+	if (pud_val(pudp[pud_index]) == 0) {
+		pmdp = (pmd_t *) get_safe_page(GFP_ATOMIC);
+		if (!pmdp)
+			return -ENOMEM;
+
+		memset(pmdp, 0, PAGE_SIZE);
+		pudp[pud_index] = pfn_pud(PFN_DOWN(__pa(pmdp)), PAGE_TABLE);
+	} else {
+		pmdp = (pmd_t *) __va(PFN_PHYS(_pud_pfn(pudp[pud_index])));
+	}
+
+	return temp_pgtable_map_pmd(pmdp, vaddr, prot);
+}
+
+static unsigned long temp_pgtable_map_p4d(p4d_t *p4dp, unsigned long vaddr, pgprot_t prot)
+{
+	uintptr_t p4d_index = p4d_index(vaddr);
+	pud_t *pudp;
+
+	if (p4d_val(p4dp[p4d_index]) == 0) {
+		pudp = (pud_t *) get_safe_page(GFP_ATOMIC);
+		if (!pudp)
+			return -ENOMEM;
+
+		memset(pudp, 0, PAGE_SIZE);
+		p4dp[p4d_index] = pfn_p4d(PFN_DOWN(__pa(pudp)), PAGE_TABLE);
+	} else {
+		pudp = (pud_t *) __va(PFN_PHYS(_p4d_pfn(p4dp[p4d_index])));
+	}
+
+	return temp_pgtable_map_pud(pudp, vaddr, prot);
+}
+
+static unsigned long temp_pgtable_map_pgd(pgd_t *pgdp, unsigned long vaddr, pgprot_t prot)
+{
+	uintptr_t pgd_idx = pgd_index(vaddr);
+	void *nextp;
+
+	if (pgd_val(pgdp[pgd_idx]) == 0) {
+		nextp = (void *) get_safe_page(GFP_ATOMIC);
+		if (!nextp)
+			return -ENOMEM;
+
+		memset(nextp, 0, PAGE_SIZE);
+		pgdp[pgd_idx] = pfn_pgd(PFN_DOWN(__pa(nextp)), PAGE_TABLE);
+	} else {
+		nextp = (void *) __va(PFN_PHYS(_pgd_pfn(pgdp[pgd_idx])));
+	}
+
+	return temp_pgtable_map_pgd_next(nextp, vaddr, prot);
+}
+
+static unsigned long temp_pgtable_mapping(pgd_t *pgdp, unsigned long vaddr, pgprot_t prot)
+{
+	return temp_pgtable_map_pgd(pgdp, vaddr, prot);
+}
+
+static unsigned long relocate_restore_code(void)
+{
+	unsigned long ret;
+	void *page = (void *)get_safe_page(GFP_ATOMIC);
+
+	if (!page)
+		return -ENOMEM;
+
+	copy_page(page, core_restore_code);
+
+	/* Make the page containing the relocated code executable */
+	set_memory_x((unsigned long)page, 1);
+
+	ret = temp_pgtable_mapping(resume_pg_dir, (unsigned long)page, PAGE_KERNEL_READ_EXEC);
+	if (ret)
+		return ret;
+
+	return (unsigned long)page;
+}
+
+int swsusp_arch_resume(void)
+{
+	unsigned long addr = PAGE_OFFSET;
+	unsigned long ret;
+
+	/*
+	 * Memory allocated by get_safe_page() will be dealt with by the hibernation core,
+	 * we don't need to free it here.
+	 */
+	resume_pg_dir = (pgd_t *)get_safe_page(GFP_ATOMIC);
+	if (!resume_pg_dir)
+		return -ENOMEM;
+
+	/*
+	 * The pages need to be wrote-able when restoring the image.
+	 * Create a second copy of page table just for the linear map, and use this when
+	 * restoring.
+	 */
+	for (; addr <= (unsigned long)pfn_to_virt(max_low_pfn); addr += PAGE_SIZE) {
+		ret = temp_pgtable_mapping(resume_pg_dir, addr, PAGE_KERNEL);
+		if (ret)
+			return (int) ret;
+	}
+
+	/* Move the restore code to a new page so that it doesn't get overwritten by itself */
+	relocated_restore_code = relocate_restore_code();
+	if (relocated_restore_code == -ENOMEM)
+		return -ENOMEM;
+
+	/* Map the __hibernate_cpu_resume() address to the temporary page table so that the
+	 * restore code can jump to it after finished restore the image. The next execution
+	 * code doesn't find itself in a different address space after switching over to the
+	 * original page table used by the hibernated image.
+	 */
+	ret = temp_pgtable_mapping(resume_pg_dir, (unsigned long)resume_hdr.restore_cpu_addr,
+				PAGE_KERNEL_READ_EXEC);
+	if (ret)
+		return ret;
+
+	restore_image(resume_hdr.saved_satp, (PFN_DOWN(__pa(resume_pg_dir)) | satp_mode),
+			resume_hdr.restore_cpu_addr);
+
+	return 0;
+}
+
+#ifdef CONFIG_SMP
+int hibernate_resume_nonboot_cpu_disable(void)
+{
+	if (sleep_cpu < 0) {
+		pr_err("Failing to resume from hibernate on an unknown CPU.\n");
+		return -ENODEV;
+	}
+
+	return freeze_secondary_cpus(sleep_cpu);
+}
+#endif
+
+static int __init riscv_hibernate__init(void)
+{
+	hibernate_cpu_context = kcalloc(1, sizeof(struct suspend_context), GFP_KERNEL);
+
+	if (WARN_ON(!hibernate_cpu_context))
+		return -ENOMEM;
+
+	return 0;
+}
+
+early_initcall(riscv_hibernate__init);
-- 
2.34.1