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SubjectRe: [PATCH 4/4] riscv: Allow NOMMU kernels to run in S-mode
On Mon, Feb 26, 2024 at 04:34:49PM -0800, Samuel Holland wrote:
> For ease of testing, it is convenient to run NOMMU kernels in supervisor
> mode. The only required change is to offset the kernel load address,
> since the beginning of RAM is usually reserved for M-mode firmware.
>
> Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
> ---
>
> arch/riscv/Kconfig | 15 ++++++++++-----
> 1 file changed, 10 insertions(+), 5 deletions(-)
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index ef53c00470d6..0dc09b2ac2f6 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -64,7 +64,7 @@ config RISCV
> select ARCH_WANTS_THP_SWAP if HAVE_ARCH_TRANSPARENT_HUGEPAGE
> select BINFMT_FLAT_NO_DATA_START_OFFSET if !MMU
> select BUILDTIME_TABLE_SORT if MMU
> - select CLINT_TIMER if !MMU
> + select CLINT_TIMER if RISCV_M_MODE
> select CLONE_BACKWARDS
> select COMMON_CLK
> select CPU_PM if CPU_IDLE || HIBERNATION || SUSPEND
> @@ -220,8 +220,12 @@ config ARCH_MMAP_RND_COMPAT_BITS_MAX
>
> # set if we run in machine mode, cleared if we run in supervisor mode
> config RISCV_M_MODE
> - bool
> - default !MMU
> + bool "Build a kernel that runs in machine mode"
> + depends on !MMU
> + default y
> + help
> + Select this option if you want to run the kernel in M-mode,
> + without the assistance of any other firmware.
>
> # set if we are running in S-mode and can use SBI calls
> config RISCV_SBI
> @@ -238,8 +242,9 @@ config MMU
>
> config PAGE_OFFSET
> hex
> - default 0xC0000000 if 32BIT && MMU
> - default 0x80000000 if !MMU
> + default 0x80000000 if !MMU && RISCV_M_MODE
> + default 0x80200000 if !MMU
> + default 0xc0000000 if 32BIT
> default 0xff60000000000000 if 64BIT

The first default seen with a passing condition is the default chosen,
right?

Cheers,
Conor.
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