[XTENSA] Add support for cache-aliasing

Add support for processors that have cache-aliasing issues, such as
the Stretch S5000 processor. Cache-aliasing means that the size of
the cache (for one way) is larger than the page size, thus, a page
can end up in several places in cache depending on the virtual to
physical translation. The method used here is to map a user page
temporarily through the auto-refill way 0 and of of the DTLB.
We probably will want to revisit this issue and use a better
approach with kmap/kunmap.

Signed-off-by: Chris Zankel <chris@zankel.net>

1 files changed, 71 insertions, 4 deletions

diff --git a/arch/xtensa/kernel/entry.S b/arch/xtensa/kernel/entry.S
index 65741e3368e7..91a689eca43d 100644
--- a/arch/xtensa/kernel/entry.S
+++ b/arch/xtensa/kernel/entry.S
@@ -7,7 +7,7 @@
  * License.  See the file "COPYING" in the main directory of this archive
  * for more details.
  *
- * Copyright (C) 2004-2005 by Tensilica Inc.
+ * Copyright (C) 2004-2007 by Tensilica Inc.
  *
  * Chris Zankel <chris@zankel.net>
  *
@@ -169,7 +169,7 @@ _user_exception:
          * We have to save all registers up to the first '1' from
          * the right, except the current frame (bit 0).
          * Assume a2 is:  001001000110001
-         * All regiser frames starting from the top fiel to the marked '1'
+         * All register frames starting from the top field to the marked '1'
          * must be saved.
          */
 
@@ -1590,7 +1590,7 @@ ENTRY(fast_second_level_miss)
          * The messy computation for 'pteval' above really simplifies
          * into the following:
          *
-         * pteval = ((pmdval - PAGE_OFFSET) & PAGE_MASK) | PAGE_KERNEL
+         * pteval = ((pmdval - PAGE_OFFSET) & PAGE_MASK) | PAGE_DIRECTORY
          */
 
         movi    a1, -PAGE_OFFSET
@@ -1602,7 +1602,7 @@ ENTRY(fast_second_level_miss)
         or      a0, a0, a1              # ... | PAGE_DIRECTORY
 
         /*
-         * We utilize all three wired-ways (7-9( to hold pmd translations.
+         * We utilize all three wired-ways (7-9) to hold pmd translations.
          * Memory regions are mapped to the DTLBs according to bits 28 and 29.
          * This allows to map the three most common regions to three different
          * DTLBs:
@@ -1652,6 +1652,73 @@ ENTRY(fast_second_level_miss)
 9:      l32i    a0, a1, TASK_ACTIVE_MM  # unlikely case mm == 0
         j       8b
 
+#if (DCACHE_WAY_SIZE > PAGE_SIZE)
+
+2:      /* Special case for cache aliasing.
+         * We (should) only get here if a clear_user_page, copy_user_page
+         * or the aliased cache flush functions got preemptively interrupted 
+         * by another task. Re-establish temporary mapping to the 
+         * TLBTEMP_BASE areas.
+         */
+
+        /* We shouldn't be in a double exception */
+
+        l32i    a0, a2, PT_DEPC
+        bgeui   a0, VALID_DOUBLE_EXCEPTION_ADDRESS, 2f
+
+        /* Make sure the exception originated in the special functions */
+
+        movi    a0, __tlbtemp_mapping_start
+        rsr     a3, EPC_1
+        bltu    a3, a0, 2f
+        movi    a0, __tlbtemp_mapping_end
+        bgeu    a3, a0, 2f
+
+        /* Check if excvaddr was in one of the TLBTEMP_BASE areas. */
+
+        movi    a3, TLBTEMP_BASE_1
+        rsr     a0, EXCVADDR
+        bltu    a0, a3, 2f
+
+        addi    a1, a0, -(2 << (DCACHE_ALIAS_ORDER + PAGE_SHIFT))
+        bgeu    a1, a3, 2f
+
+        /* Check if we have to restore an ITLB mapping. */
+
+        movi    a1, __tlbtemp_mapping_itlb
+        rsr     a3, EPC_1
+        sub     a3, a3, a1
+
+        /* Calculate VPN */
+
+        movi    a1, PAGE_MASK
+        and     a1, a1, a0
+
+        /* Jump for ITLB entry */
+
+        bgez    a3, 1f
+
+        /* We can use up to two TLBTEMP areas, one for src and one for dst. */
+
+        extui   a3, a0, PAGE_SHIFT + DCACHE_ALIAS_ORDER, 1
+        add     a1, a3, a1
+
+        /* PPN is in a6 for the first TLBTEMP area and in a7 for the second. */
+
+        mov     a0, a6
+        movnez  a0, a7, a3
+        j       3b
+
+        /* ITLB entry. We only use dst in a6. */
+
+1:      witlb   a6, a1
+        isync
+        j       4b
+
+
+#endif  // DCACHE_WAY_SIZE > PAGE_SIZE
+
+
 2:      /* Invalid PGD, default exception handling */
 
         movi    a3, exc_table