diff --git a/arch/arm/include/asm/memory.h b/arch/arm/include/asm/memory.h
index c79b57bf71c40d1fc2083f67b198377936e0002f..49bf6b1e2177d6dc049baf014dc42a3971f6b6b0 100644
--- a/arch/arm/include/asm/memory.h
+++ b/arch/arm/include/asm/memory.h
@@ -273,14 +273,14 @@ static inline void *phys_to_virt(phys_addr_t x)
 #define __va(x)			((void *)__phys_to_virt((phys_addr_t)(x)))
 #define pfn_to_kaddr(pfn)	__va((phys_addr_t)(pfn) << PAGE_SHIFT)
 
-extern phys_addr_t (*arch_virt_to_idmap)(unsigned long x);
+extern unsigned long (*arch_virt_to_idmap)(unsigned long x);
 
 /*
  * These are for systems that have a hardware interconnect supported alias of
  * physical memory for idmap purposes.  Most cases should leave these
- * untouched.
+ * untouched.  Note: this can only return addresses less than 4GiB.
  */
-static inline phys_addr_t __virt_to_idmap(unsigned long x)
+static inline unsigned long __virt_to_idmap(unsigned long x)
 {
 	if (IS_ENABLED(CONFIG_MMU) && arch_virt_to_idmap)
 		return arch_virt_to_idmap(x);
diff --git a/arch/arm/kernel/reboot.c b/arch/arm/kernel/reboot.c
index 38269358fd252c6bb93fd58a0478319c436cdfd3..71a2ff9ec4900c58677f12114c85c82e8cfaa575 100644
--- a/arch/arm/kernel/reboot.c
+++ b/arch/arm/kernel/reboot.c
@@ -50,7 +50,7 @@ static void __soft_restart(void *addr)
 	flush_cache_all();
 
 	/* Switch to the identity mapping. */
-	phys_reset = (phys_reset_t)(unsigned long)virt_to_idmap(cpu_reset);
+	phys_reset = (phys_reset_t)virt_to_idmap(cpu_reset);
 	phys_reset((unsigned long)addr);
 
 	/* Should never get here. */
diff --git a/arch/arm/mach-keystone/keystone.c b/arch/arm/mach-keystone/keystone.c
index c279293f084cb87c2e0cc4cbf4ada1e2984e83f2..d80879ce4963b368a212747920982c268400dc1b 100644
--- a/arch/arm/mach-keystone/keystone.c
+++ b/arch/arm/mach-keystone/keystone.c
@@ -63,7 +63,7 @@ static void __init keystone_init(void)
 	of_platform_populate(NULL, of_default_bus_match_table, NULL, NULL);
 }
 
-static phys_addr_t keystone_virt_to_idmap(unsigned long x)
+static unsigned long keystone_virt_to_idmap(unsigned long x)
 {
 	return (phys_addr_t)(x) - CONFIG_PAGE_OFFSET + KEYSTONE_LOW_PHYS_START;
 }
diff --git a/arch/arm/mm/idmap.c b/arch/arm/mm/idmap.c
index d65909697165b20cc1936f50073bd3eea7521aec..bd274a05b8ffa9446160d1de69f777d9431c629b 100644
--- a/arch/arm/mm/idmap.c
+++ b/arch/arm/mm/idmap.c
@@ -15,7 +15,7 @@
  * page tables.
  */
 pgd_t *idmap_pgd;
-phys_addr_t (*arch_virt_to_idmap) (unsigned long x);
+unsigned long (*arch_virt_to_idmap)(unsigned long x);
 
 #ifdef CONFIG_ARM_LPAE
 static void idmap_add_pmd(pud_t *pud, unsigned long addr, unsigned long end,