Commit 5f0fbf9e authored by Nicolas Pitre's avatar Nicolas Pitre
Browse files

[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: default avatarNicolas Pitre <>
parent 1522ac3e
......@@ -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.
#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 FIX_KMAP_BEGIN 0
#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)
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);
/* the upper-most page table pointer */
/* the upper-most page table pointer */
extern pmd_t *top_pmd;
#define TOP_PTE(x) pte_offset_kernel(top_pmd, x)
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