ARM: make virt_to_idmap() return unsigned long

Make virt_to_idmap() return an unsigned long rather than phys_addr_t.

Returning phys_addr_t here makes no sense, because the definition of
virt_to_idmap() is that it shall return a physical address which maps
identically with the virtual address.  Since virtual addresses are
limited to 32-bit, identity mapped physical addresses are as well.

Almost all users already had an implicit narrowing cast to unsigned long
so let's make this official and part of this interface.

Tested-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
diff --git a/arch/arm/include/asm/memory.h b/arch/arm/include/asm/memory.h
index c79b57b..49bf6b1 100644
--- a/arch/arm/include/asm/memory.h
+++ b/arch/arm/include/asm/memory.h
@@ -273,14 +273,14 @@
 #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);