[ARM] pgtable: file pte layout documentation
Document the layout of our file PTE entries.
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
diff --git a/arch/arm/include/asm/pgtable.h b/arch/arm/include/asm/pgtable.h
index c1d9793..c433c6c 100644
--- a/arch/arm/include/asm/pgtable.h
+++ b/arch/arm/include/asm/pgtable.h
@@ -285,15 +285,6 @@
#define pte_young(pte) (pte_val(pte) & L_PTE_YOUNG)
#define pte_special(pte) (0)
-/*
- * The following only works if pte_present() is not true.
- */
-#define pte_file(pte) (pte_val(pte) & L_PTE_FILE)
-#define pte_to_pgoff(x) (pte_val(x) >> 2)
-#define pgoff_to_pte(x) __pte(((x) << 2) | L_PTE_FILE)
-
-#define PTE_FILE_MAX_BITS 30
-
#define PTE_BIT_FUNC(fn,op) \
static inline pte_t pte_##fn(pte_t pte) { pte_val(pte) op; return pte; }
@@ -414,6 +405,20 @@
*/
#define MAX_SWAPFILES_CHECK() BUILD_BUG_ON(MAX_SWAPFILES_SHIFT > __SWP_TYPE_BITS)
+/*
+ * Encode and decode a file entry. File entries are stored in the Linux
+ * page tables as follows:
+ *
+ * 3 3 2 2 2 2 2 2 2 2 2 2 1 1 1 1 1 1 1 1 1 1
+ * 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0
+ * <------------------------ offset -------------------------> 1 0
+ */
+#define pte_file(pte) (pte_val(pte) & L_PTE_FILE)
+#define pte_to_pgoff(x) (pte_val(x) >> 2)
+#define pgoff_to_pte(x) __pte(((x) << 2) | L_PTE_FILE)
+
+#define PTE_FILE_MAX_BITS 30
+
/* Needs to be defined here and not in linux/mm.h, as it is arch dependent */
/* FIXME: this is not correct */
#define kern_addr_valid(addr) (1)