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CONFIG_INITIALIZE_XTENSA_MMU_INSIDE_VMLINUX: Initialize Xtensa MMU inside the Linux kernel code

General informations

The Linux kernel configuration item CONFIG_INITIALIZE_XTENSA_MMU_INSIDE_VMLINUX:

Help text

Earlier version initialized the MMU in the exception vector before jumping to _startup in head.S and had an advantage that it was possible to place a software breakpoint at 'reset' and then enter your normal kernel breakpoints once the MMU was mapped to the kernel mappings (0XC0000000).

This unfortunately doesn't work for U-Boot and likley also wont work for using KEXEC to have a hot kernel ready for doing a KDUMP.

So now the MMU is initialized in head.S but it's necessary to use hardware breakpoints (gdb 'hbreak' cmd) to break at _startup. xt-gdb can't place a Software Breakpoint in the 0XD region prior to mapping the MMU and after mapping even if the area of low memory was mapped gdb wouldn't remove the breakpoint on hitting it as the PC wouldn't match. Since Hardware Breakpoints are recommended for Linux configurations it seems reasonable to just assume they exist and leave this older mechanism for unfortunate souls that choose not to follow Tensilica's recommendation.

Selecting this will cause U-Boot to set the KERNEL Load and Entry address at 0x00003000 instead of the mapped std of 0xD0003000.

If in doubt, say Y.



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