[ARM] fixmap support

This is the minimum fixmap interface expected to be implemented by
architectures supporting highmem.

We have a second level page table already allocated and covering
0xfff00000-0xffffffff because the exception vector page is located
at 0xffff0000, and various cache tricks already use some entries above
0xffff0000.  Therefore the PTEs covering 0xfff00000-0xfffeffff are free
to be used.

However the XScale cache flushing code already uses virtual addresses
between 0xfffe0000 and 0xfffeffff.

So this reserves the 0xfff00000-0xfffdffff range for fixmap stuff.

The Documentation/arm/memory.txt information is updated accordingly,
including the information about the actual top of DMA memory mapping
region which didn't match the code.

Signed-off-by: Nicolas Pitre <nico@marvell.com>

3 files changed, 50 insertions, 3 deletions

diff --git a/Documentation/arm/memory.txt b/Documentation/arm/memory.txt
index dc6045577a8..43cb1004d35 100644
--- a/Documentation/arm/memory.txt
+++ b/Documentation/arm/memory.txt
@@ -29,7 +29,14 @@ ffff0000	ffff0fff	CPU vector page.
                                 CPU supports vector relocation (control
                                 register V bit.)
 
-ffc00000        fffeffff        DMA memory mapping region.  Memory returned
+fffe0000        fffeffff        XScale cache flush area.  This is used
+                                in proc-xscale.S to flush the whole data
+                                cache.  Free for other usage on non-XScale.
+
+fff00000        fffdffff        Fixmap mapping region.  Addresses provided
+                                by fix_to_virt() will be located here.
+
+ffc00000        ffefffff        DMA memory mapping region.  Memory returned
                                 by the dma_alloc_xxx functions will be
                                 dynamically mapped here.
 
diff --git a/arch/arm/include/asm/fixmap.h b/arch/arm/include/asm/fixmap.h
new file mode 100644
index 00000000000..bbae919bceb
--- /dev/null
+++ b/arch/arm/include/asm/fixmap.h
@@ -0,0 +1,41 @@
+#ifndef _ASM_FIXMAP_H
+#define _ASM_FIXMAP_H
+
+/*
+ * Nothing too fancy for now.
+ *
+ * On ARM we already have well known fixed virtual addresses imposed by
+ * the architecture such as the vector page which is located at 0xffff0000,
+ * therefore a second level page table is already allocated covering
+ * 0xfff00000 upwards.
+ *
+ * The cache flushing code in proc-xscale.S uses the virtual area between
+ * 0xfffe0000 and 0xfffeffff.
+ */
+
+#define FIXADDR_START           0xfff00000UL
+#define FIXADDR_TOP             0xfffe0000UL
+#define FIXADDR_SIZE            (FIXADDR_TOP - FIXADDR_START)
+
+#define FIX_KMAP_BEGIN          0
+#define FIX_KMAP_END            (FIXADDR_SIZE >> PAGE_SHIFT)
+
+#define __fix_to_virt(x)        (FIXADDR_START + ((x) << PAGE_SHIFT))
+#define __virt_to_fix(x)        (((x) - FIXADDR_START) >> PAGE_SHIFT)
+
+extern void __this_fixmap_does_not_exist(void);
+
+static inline unsigned long fix_to_virt(const unsigned int idx)
+{
+        if (idx >= FIX_KMAP_END)
+                __this_fixmap_does_not_exist();
+        return __fix_to_virt(idx);
+}
+
+static inline unsigned int virt_to_fix(const unsigned long vaddr)
+{
+        BUG_ON(vaddr >= FIXADDR_TOP || vaddr < FIXADDR_START);
+        return __virt_to_fix(vaddr);
+}
+
+#endif
diff --git a/arch/arm/mm/mm.h b/arch/arm/mm/mm.h
index 95bbe112965..c4f6f05198e 100644
--- a/arch/arm/mm/mm.h
+++ b/arch/arm/mm/mm.h
@@ -1,7 +1,6 @@
-/* the upper-most page table pointer */
-
 #ifdef CONFIG_MMU
 
+/* the upper-most page table pointer */
 extern pmd_t *top_pmd;
 
 #define TOP_PTE(x)      pte_offset_kernel(top_pmd, x)