Lee Lup Yuen
62c358946d
Ox64 BL808 crashes with a Page Fault when we run `getprime` then `hello`. This is caused by the T-Head C906 MMU incorrectly accessing the MMU Page Tables of the Previous Process (`getprime`) while starting the New Process (`hello`). To fix the problem, this PR flushes the MMU Cache whenever we point the MMU SATP Register to the New Page Tables. We execute 2 RISC-V Instructions that are specific to T-Head C906: - DCACHE.IALL: Invalidate all Page Table Entries in the D-Cache - SYNC.S: Ensure that all Cache Operations are completed This is derived from the T-Head Errata for Linux Kernel. More details here: https://lupyuen.github.io/articles/mmu#appendix-flush-the-mmu-cache-for-t-head-c906 Modified Files: - `arch/risc-v/src/common/riscv_mmu.h`: If needed, `mmu_write_satp()` calls `mmu_flush_cache()` (weak function) to flush the MMU Cache. (Like for T-Head C906) - `arch/risc-v/src/bl808/bl808_mm_init.c`: Flush the MMU Cache for T-Head C906. Extend `mmuflags` from 32-bit to 64-bit to be consistent with `mmu_ln_setentry()`. - `boards/risc-v/bl808/ox64/configs/nsh/defconfig`: Enable `ostest` in the Build Config. Update `CONFIG_BOARD_LOOPSPERMSEC` according to `calib_udelay`.
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