Add some brief documentation on using dump_pagetables() to print out U-Boot's pagetables during boot.
Signed-off-by: Caleb Connolly caleb.connolly@linaro.org --- doc/arch/arm64.rst | 49 +++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 49 insertions(+)
diff --git a/doc/arch/arm64.rst b/doc/arch/arm64.rst index 7c0713504c47..19662be6fc6e 100644 --- a/doc/arch/arm64.rst +++ b/doc/arch/arm64.rst @@ -47,8 +47,57 @@ Notes
6. CONFIG_ARM64 instead of CONFIG_ARMV8 is used to distinguish aarch64 and aarch32 specific codes.
+MMU +--- + +U-Boot uses a simple page table for MMU setup. It uses the smallest number of bits +possible for the virtual address based on the maximum memory address (see the logic +in ``get_tcr()``). If this is less than 39 bits, the MMU will use only 3 levels for +address translation. + +As with all platforms, U-Boot on ARM64 uses a 1:1 mapping of virtual to physical addresses. +In general, the memory map is expected to remain static once the MMU is enabled. + +Software pagetable walker +^^^^^^^^^^^^^^^^^^^^^^^^^ + +It is possible to debug the pagetable generated by U-Boot with the built in +``dump_pagetable()`` and ``walk_pagetable()`` functions (the former being a simple +wrapper for the latter). For example the following can be added to ``setup_all_pgtables()`` +after the first call to ``setup_pgtables()``: + +.. code-block:: c + + dump_pagetable(gd->arch.tlb_addr, get_tcr(NULL, NULL)); + +.. kernel-doc:: arch/arm/cpu/armv8/cache_v8.c + :identifiers: __pagetable_walk pagetable_print_entry + +The pagetable walker can be used as follows: + +.. kernel-doc:: arch/arm/include/asm/armv8/mmu.h + :identifiers: pte_walker_cb_t walk_pagetable dump_pagetable + +This will result in a print like the following: + +.. code-block:: text + + Walking pagetable at 000000017df90000, va_bits: 36. Using 3 levels + [0x17df91000] | Table | | + [0x17df92000] | Table | | + [0x000001000 - 0x000200000] | Pages | Device-nGnRnE | Non-shareable + [0x000200000 - 0x040000000] | Block | Device-nGnRnE | Non-shareable + [0x040000000 - 0x080000000] | Block | Device-nGnRnE | Non-shareable + [0x080000000 - 0x140000000] | Block | Normal | Inner-shareable + [0x17df93000] | Table | | + [0x140000000 - 0x17de00000] | Block | Normal | Inner-shareable + [0x17df94000] | Table | | + [0x17de00000 - 0x17dfa0000] | Pages | Normal | Inner-shareable + +For more information, please refer to the additional function documentation in +``arch/arm/include/asm/armv8/mmu.h``.
Contributors ------------ * Tom Rini trini@ti.com