2.5.75

 arch

 cris

diff -Nru a/arch/cris/README.mm b/arch/cris/README.mm
--- a/arch/cris/README.mm   Thu Jul 10 13:16:28 2003
+++ /dev/null   Wed Dec 31 16:00:00 1969
@@ -1,244 +0,0 @@
-Memory management for CRIS/MMU
-------------------------------
-HISTORY:
-
-$Log: README.mm,v $
-Revision 1.1.1.1  2001/12/17 13:59:27  bjornw
-Import of Linux 2.5.1
-
-Revision 1.1  2000/07/10 16:25:21  bjornw
-Initial revision
-
-Revision 1.4  2000/01/17 02:31:59  bjornw
-Added discussion of paging and VM.
-
-Revision 1.3  1999/12/03 16:43:23  hp
-Blurb about that the 3.5G-limitation is not a MMU limitation
-
-Revision 1.2  1999/12/03 16:04:21  hp
-Picky comment about not mapping the first page
-
-Revision 1.1  1999/12/03 15:41:30  bjornw
-First version of CRIS/MMU memory layout specification.
-
-
-
-
-
-------------------------------
-
-See the ETRAX-NG HSDD for reference.
-
-We use the page-size of 8 kbytes, as opposed to the i386 page-size of 4 kbytes.
-
-The MMU can, apart from the normal mapping of pages, also do a top-level
-segmentation of the kernel memory space. We use this feature to avoid having
-to use page-tables to map the physical memory into the kernel's address
-space. We also use it to keep the user-mode virtual mapping in the same
-map during kernel-mode, so that the kernel easily can access the corresponding
-user-mode process' data.
-
-As a comparision, the Linux/i386 2.0 puts the kernel and physical RAM at
-address 0, overlapping with the user-mode virtual space, so that descriptor
-registers are needed for each memory access to specify which MMU space to
-map through. That changed in 2.2, putting the kernel/physical RAM at 
-0xc0000000, to co-exist with the user-mode mapping. We will do something
-quite similar, but with the additional complexity of having to map the
-internal chip I/O registers and the flash memory area (including SRAM
-and peripherial chip-selets).
-
-The kernel-mode segmentation map:
-
-        ------------------------                ------------------------
-FFFFFFFF|                      | => cached      |                      | 
-        |    kernel seg_f      |    flash       |                      |
-F0000000|______________________|                |                      |
-EFFFFFFF|                      | => uncached    |                      | 
-        |    kernel seg_e      |    flash       |                      |
-E0000000|______________________|                |        DRAM          |
-DFFFFFFF|                      |  paged to any  |      Un-cached       | 
-        |    kernel seg_d      |    =======>    |                      |
-D0000000|______________________|                |                      |
-CFFFFFFF|                      |                |                      | 
-        |    kernel seg_c      |==\             |                      |
-C0000000|______________________|   \            |______________________|
-BFFFFFFF|                      |  uncached      |                      |
-        |    kernel seg_b      |=====\=========>|       Registers      |
-B0000000|______________________|      \c        |______________________|
-AFFFFFFF|                      |       \a       |                      |
-        |                      |        \c      | FLASH/SRAM/Peripheral|
-        |                      |         \h     |______________________|
-        |                      |          \e    |                      |
-        |                      |           \d   |                      |
-        | kernel seg_0 - seg_a |            \==>|         DRAM         | 
-        |                      |                |        Cached        |
-        |                      |  paged to any  |                      |
-        |                      |    =======>    |______________________| 
-        |                      |                |                      |
-        |                      |                |        Illegal       |
-        |                      |                |______________________|
-        |                      |                |                      |      
-        |                      |                | FLASH/SRAM/Peripheral|
-00000000|______________________|                |______________________|
-
-In user-mode it looks the same except that only the space 0-AFFFFFFF is
-available. Therefore, in this model, the virtual address space per process
-is limited to 0xb0000000 bytes (minus 8192 bytes, since the first page,
-0..8191, is never mapped, in order to trap NULL references).
-
-It also means that the total physical RAM that can be mapped is 256 MB
-(kseg_c above). More RAM can be mapped by choosing a different segmentation
-and shrinking the user-mode memory space.
-
-The MMU can map all 4 GB in user mode, but doing that would mean that a
-few extra instructions would be needed for each access to user mode
-memory.
-
-The kernel needs access to both cached and uncached flash. Uncached is
-necessary because of the special write/erase sequences. Also, the 
-peripherial chip-selects are decoded from that region.
-
-The kernel also needs its own virtual memory space. That is kseg_d. It
-is used by the vmalloc() kernel function to allocate virtual contiguous
-chunks of memory not possible using the normal kmalloc physical RAM 
-allocator.
-
-The setting of the actual MMU control registers to use this layout would
-be something like this:
-
-R_MMU_KSEG = ( ( seg_f, seg     ) |   // Flash cached
-               ( seg_e, seg     ) |   // Flash uncached
-               ( seg_d, page    ) |   // kernel vmalloc area    
-               ( seg_c, seg     ) |   // kernel linear segment
-               ( seg_b, seg     ) |   // kernel linear segment
-               ( seg_a, page    ) |
-               ( seg_9, page    ) |
-               ( seg_8, page    ) |
-               ( seg_7, page    ) |
-               ( seg_6, page    ) |
-               ( seg_5, page    ) |
-               ( seg_4, page    ) |
-               ( seg_3, page    ) |
-               ( seg_2, page    ) |
-               ( seg_1, page    ) |
-               ( seg_0, page    ) );
-
-R_MMU_KBASE_HI = ( ( base_f, 0x0 ) |   // flash/sram/periph cached
-                   ( base_e, 0x8 ) |   // flash/sram/periph uncached
-                   ( base_d, 0x0 ) |   // don't care
-                   ( base_c, 0x4 ) |   // physical RAM cached area
-                   ( base_b, 0xb ) |   // uncached on-chip registers
-                   ( base_a, 0x0 ) |   // don't care
-                   ( base_9, 0x0 ) |   // don't care
-                   ( base_8, 0x0 ) );  // don't care
-
-R_MMU_KBASE_LO = ( ( base_7, 0x0 ) |   // don't care
-                   ( base_6, 0x0 ) |   // don't care
-                   ( base_5, 0x0 ) |   // don't care
-                   ( base_4, 0x0 ) |   // don't care
-                   ( base_3, 0x0 ) |   // don't care
-                   ( base_2, 0x0 ) |   // don't care
-                   ( base_1, 0x0 ) |   // don't care
-                   ( base_0, 0x0 ) );  // don't care
-
-NOTE: while setting up the MMU, we run in a non-mapped mode in the DRAM (0x40
-segment) and need to setup the seg_4 to a unity mapping, so that we don't get
-a fault before we have had time to jump into the real kernel segment (0xc0). This
-is done in head.S temporarily, but fixed by the kernel later in paging_init.
-
-
-Paging - PTE's, PMD's and PGD's
--------------------------------
-
-[ References: asm/pgtable.h, asm/page.h, asm/mmu.h ]
-
-The paging mechanism uses virtual addresses to split a process memory-space into
-pages, a page being the smallest unit that can be freely remapped in memory. On
-Linux/CRIS, a page is 8192 bytes (for technical reasons not equal to 4096 as in 
-most other 32-bit architectures). It would be inefficient to let a virtual memory
-mapping be controlled by a long table of page mappings, so it is broken down into
-a 2-level structure with a Page Directory containing pointers to Page Tables which
-each have maps of up to 2048 pages (8192 / sizeof(void *)). Linux can actually
-handle 3-level structures as well, with a Page Middle Directory in between, but
-in many cases, this is folded into a two-level structure by excluding the Middle
-Directory.
-
-We'll take a look at how an address is translated while we discuss how it's handled
-in the Linux kernel.
-
-The example address is 0xd004000c; in binary this is:
-
-31       23       15       7      0
-11010000 00000100 00000000 00001100
-
-|______| |__________||____________|
-  PGD        PTE       page offset
-
-Given the top-level Page Directory, the offset in that directory is calculated
-using the upper 8 bits:
-
-extern inline pgd_t * pgd_offset(struct mm_struct * mm, unsigned long address)
-{
-   return mm->pgd + (address >> PGDIR_SHIFT);
-}
-
-PGDIR_SHIFT is the log2 of the amount of memory an entry in the PGD can map; in our
-case it is 24, corresponding to 16 MB. This means that each entry in the PGD 
-corresponds to 16 MB of virtual memory.
-
-The pgd_t from our example will therefore be the 208'th (0xd0) entry in mm->pgd.
-
-Since the Middle Directory does not exist, it is a unity mapping:
-
-extern inline pmd_t * pmd_offset(pgd_t * dir, unsigned long address)
-{
-   return (pmd_t *) dir;
-}
-
-The Page Table provides the final lookup by using bits 13 to 23 as index:
-
-extern inline pte_t * pte_offset(pmd_t * dir, unsigned long address)
-{
-   return (pte_t *) pmd_page(*dir) + ((address >> PAGE_SHIFT) &
-                  (PTRS_PER_PTE - 1));
-}
-
-PAGE_SHIFT is the log2 of the size of a page; 13 in our case. PTRS_PER_PTE is
-the number of pointers that fit in a Page Table and is used to mask off the 
-PGD-part of the address.
-
-The so-far unused bits 0 to 12 are used to index inside a page linearily.
-
-The VM system
--------------
-
-The kernels own page-directory is the swapper_pg_dir, cleared in paging_init, 
-and contains the kernels virtual mappings (the kernel itself is not paged - it
-is mapped linearily using kseg_c as described above). Architectures without
-kernel segments like the i386, need to setup swapper_pg_dir directly in head.S
-to map the kernel itself. swapper_pg_dir is pointed to by init_mm.pgd as the
-init-task's PGD.
-
-To see what support functions are used to setup a page-table, let's look at the
-kernel's internal paged memory system, vmalloc/vfree.
-
-void * vmalloc(unsigned long size)
-
-The vmalloc-system keeps a paged segment in kernel-space at 0xd0000000. What
-happens first is that a virtual address chunk is allocated to the request using
-get_vm_area(size). After that, physical RAM pages are allocated and put into
-the kernel's page-table using alloc_area_pages(addr, size). 
-
-static int alloc_area_pages(unsigned long address, unsigned long size)
-
-First the PGD entry is found using init_mm.pgd. This is passed to
-alloc_area_pmd (remember the 3->2 folding). It uses pte_alloc_kernel to
-check if the PGD entry points anywhere - if not, a page table page is
-allocated and the PGD entry updated. Then the alloc_area_pte function is
-used just like alloc_area_pmd to check which page table entry is desired, 
-and a physical page is allocated and the table entry updated. All of this
-is repeated at the top-level until the entire address range specified has 
-been mapped.
-
-
-