On Fri, Jun 07, 2024 at 10:42:51PM +0200, Caleb Connolly wrote:
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 | 37 +++++++++++++++++++++++++++++++++++++ 1 file changed, 37 insertions(+)
diff --git a/doc/arch/arm64.rst b/doc/arch/arm64.rst index 7c0713504c47..0c851304aad4 100644 --- a/doc/arch/arm64.rst +++ b/doc/arch/arm64.rst @@ -47,8 +47,45 @@ Notes
- 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()``).
+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.
+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));
+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 function documentation in +``arch/arm/include/asm/armv8/mmu.h``.
Since the function comments are kernel-doc style, can you please rework this to leverage "kernel-doc::" and make sure it renders nicely? And this may show we should be putting some function comments in 2/3 of this series as well.