sh: Free up some and document PTEL flags.

Drop _PAGE_SHARED/_PAGE_U0_SHARED and document Linux PTE encodings in
the PTEL value. Preserve the swap cache entry encoding semantics for
now, though it will need rework to free up _PAGE_WT from _PAGE_FILE.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>

1 files changed, 45 insertions, 31 deletions

diff --git a/include/asm-sh/pgtable.h b/include/asm-sh/pgtable.h
index 9728b58f7c1..41c559d8ba8 100644
--- a/include/asm-sh/pgtable.h
+++ b/include/asm-sh/pgtable.h
@@ -54,20 +54,41 @@ extern unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)];
 #define VMALLOC_START   (P3SEG+0x00100000)
 #define VMALLOC_END     (FIXADDR_START-2*PAGE_SIZE)
 
-#define _PAGE_WT        0x001  /* WT-bit on SH-4, 0 on SH-3 */
-#define _PAGE_HW_SHARED 0x002  /* SH-bit  : page is shared among processes */
-#define _PAGE_DIRTY     0x004  /* D-bit   : page changed */
-#define _PAGE_CACHABLE  0x008  /* C-bit   : cachable */
-#define _PAGE_SZ0       0x010  /* SZ0-bit : Size of page */
-#define _PAGE_RW        0x020  /* PR0-bit : write access allowed */
-#define _PAGE_USER      0x040  /* PR1-bit : user space access allowed */
-#define _PAGE_SZ1       0x080  /* SZ1-bit : Size of page (on SH-4) */
-#define _PAGE_PRESENT   0x100  /* V-bit   : page is valid */
-#define _PAGE_PROTNONE  0x200  /* software: if not present  */
-#define _PAGE_ACCESSED  0x400  /* software: page referenced */
-#define _PAGE_U0_SHARED 0x800  /* software: page is shared in user space */
-
-#define _PAGE_FILE      _PAGE_WT  /* software: pagecache or swap? */
+/*
+ * Linux PTEL encoding.
+ *
+ * Hardware and software bit definitions for the PTEL value:
+ *
+ * - Bits 0 and 7 are reserved on SH-3 (_PAGE_WT and _PAGE_SZ1 on SH-4).
+ *
+ * - Bit 1 is the SH-bit, but is unused on SH-3 due to an MMU bug (the
+ *   hardware PTEL value can't have the SH-bit set when MMUCR.IX is set,
+ *   which is the default in cpu-sh3/mmu_context.h:MMU_CONTROL_INIT).
+ *
+ *   In order to keep this relatively clean, do not use these for defining
+ *   SH-3 specific flags until all of the other unused bits have been
+ *   exhausted.
+ *
+ * - Bit 9 is reserved by everyone and used by _PAGE_PROTNONE.
+ *
+ * - Bits 10 and 11 are low bits of the PPN that are reserved on >= 4K pages.
+ *   Bit 10 is used for _PAGE_ACCESSED, bit 11 remains unused.
+ *
+ * - Bits 31, 30, and 29 remain unused by everyone and can be used for future
+ *   software flags, although care must be taken to update _PAGE_CLEAR_FLAGS.
+ */
+#define _PAGE_WT        0x001           /* WT-bit on SH-4, 0 on SH-3 */
+#define _PAGE_HW_SHARED 0x002           /* SH-bit  : shared among processes */
+#define _PAGE_DIRTY     0x004           /* D-bit   : page changed */
+#define _PAGE_CACHABLE  0x008           /* C-bit   : cachable */
+#define _PAGE_SZ0       0x010           /* SZ0-bit : Size of page */
+#define _PAGE_RW        0x020           /* PR0-bit : write access allowed */
+#define _PAGE_USER      0x040           /* PR1-bit : user space access allowed */
+#define _PAGE_SZ1       0x080           /* SZ1-bit : Size of page (on SH-4) */
+#define _PAGE_PRESENT   0x100           /* V-bit   : page is valid */
+#define _PAGE_PROTNONE  0x200           /* software: if not present  */
+#define _PAGE_ACCESSED  0x400           /* software: page referenced */
+#define _PAGE_FILE      _PAGE_WT        /* software: pagecache or swap? */
 
 /* software: moves to PTEA.TC (Timing Control) */
 #define _PAGE_PCC_AREA5 0x00000000      /* use BSC registers for area5 */
@@ -82,22 +103,17 @@ extern unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)];
 #define _PAGE_PCC_ATR8  0x60000000      /* Attribute Memory space, 8 bit bus */
 #define _PAGE_PCC_ATR16 0x60000001      /* Attribute Memory space, 6 bit bus */
 
-/* Mask which drop software flags
- * We also drop WT bit since it is used for _PAGE_FILE
- * bit in this implementation.
- */
-#define _PAGE_CLEAR_FLAGS       (_PAGE_WT | _PAGE_PROTNONE | _PAGE_ACCESSED | _PAGE_U0_SHARED)
-
-#if defined(CONFIG_CPU_SH3)
-/*
- * MMU on SH-3 has bug on SH-bit: We can't use it if MMUCR.IX=1.
- * Work around: Just drop SH-bit.
- */
-#define _PAGE_FLAGS_HARDWARE_MASK       (0x1fffffff & ~(_PAGE_CLEAR_FLAGS | _PAGE_HW_SHARED))
+/* Mask which drops unused bits from the PTEL value */
+#ifdef CONFIG_CPU_SH3
+#define _PAGE_CLEAR_FLAGS       (_PAGE_PROTNONE | _PAGE_ACCESSED| \
+                                 _PAGE_FILE     | _PAGE_SZ1     | \
+                                 _PAGE_HW_SHARED)
 #else
-#define _PAGE_FLAGS_HARDWARE_MASK       (0x1fffffff & ~(_PAGE_CLEAR_FLAGS))
+#define _PAGE_CLEAR_FLAGS       (_PAGE_PROTNONE | _PAGE_ACCESSED | _PAGE_FILE)
 #endif
 
+#define _PAGE_FLAGS_HARDWARE_MASK       (0x1fffffff & ~(_PAGE_CLEAR_FLAGS))
+
 /* Hardware flags: SZ0=1 (4k-byte) */
 #define _PAGE_FLAGS_HARD        _PAGE_SZ0
 
@@ -107,17 +123,15 @@ extern unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)];
 #define _PAGE_SZHUGE    (_PAGE_SZ0 | _PAGE_SZ1)
 #endif
 
-#define _PAGE_SHARED    _PAGE_U0_SHARED
-
 #define _PAGE_TABLE     (_PAGE_PRESENT | _PAGE_RW | _PAGE_USER | _PAGE_ACCESSED | _PAGE_DIRTY)
 #define _KERNPG_TABLE   (_PAGE_PRESENT | _PAGE_RW | _PAGE_ACCESSED | _PAGE_DIRTY)
-#define _PAGE_CHG_MASK  (PTE_MASK | _PAGE_ACCESSED | _PAGE_CACHABLE | _PAGE_DIRTY | _PAGE_SHARED)
+#define _PAGE_CHG_MASK  (PTE_MASK | _PAGE_ACCESSED | _PAGE_CACHABLE | _PAGE_DIRTY)
 
 #ifndef __ASSEMBLY__
 
 #ifdef CONFIG_MMU
 #define PAGE_NONE       __pgprot(_PAGE_PROTNONE | _PAGE_CACHABLE |_PAGE_ACCESSED | _PAGE_FLAGS_HARD)
-#define PAGE_SHARED     __pgprot(_PAGE_PRESENT | _PAGE_RW | _PAGE_USER | _PAGE_CACHABLE |_PAGE_ACCESSED | _PAGE_SHARED | _PAGE_FLAGS_HARD)
+#define PAGE_SHARED     __pgprot(_PAGE_PRESENT | _PAGE_RW | _PAGE_USER | _PAGE_CACHABLE |_PAGE_ACCESSED | _PAGE_FLAGS_HARD)
 #define PAGE_COPY       __pgprot(_PAGE_PRESENT | _PAGE_USER | _PAGE_CACHABLE | _PAGE_ACCESSED | _PAGE_FLAGS_HARD)
 #define PAGE_READONLY   __pgprot(_PAGE_PRESENT | _PAGE_USER | _PAGE_CACHABLE | _PAGE_ACCESSED | _PAGE_FLAGS_HARD)
 #define PAGE_KERNEL     __pgprot(_PAGE_PRESENT | _PAGE_RW | _PAGE_CACHABLE | _PAGE_DIRTY | _PAGE_ACCESSED | _PAGE_HW_SHARED | _PAGE_FLAGS_HARD)