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Reasons for this involves lack of users as well as maintenance > efforts to support this mode. psABI FDPIC specification also never > made it upstream and last public messages of this development seems to > date back from 2020 [2]. Plan the deprecation to be done in 2 years from What are the criteria for delaying/canceling the removal? NOMMU support doesn't rot nearly as fast as XIP; static PIE ELF works and is well specified; and as mentioned at LPC, there are some users, even if "just for fun". > now. Mark the Kconfig option as deprecated by adding a new dummy option > which explicitly displays the deprecation in case of CONFIG_MMU=n. This option > is selected indirectly by CONFIG_RISCV_M_MODE since an option can not > select another one directly with a "select" in case of such CONFIG=n. > Additionally, display a pr_err() message at boot time in case of NOMMU > build to warn about upcoming deprecation. > > Link: https://lpc.events/event/17/contributions/1478/ [1] > Link: https://groups.google.com/a/groups.riscv.org/g/sw-dev/c/ZjYUJswknQ4/m/WYRRylTwAAAJ [2] > Signed-off-by: Clément Léger > > --- > arch/riscv/Kconfig | 8 ++++++++ > arch/riscv/kernel/setup.c | 4 ++++ > 2 files changed, 12 insertions(+) > > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig > index bffbd869a068..8da58c102d3f 100644 > --- a/arch/riscv/Kconfig > +++ b/arch/riscv/Kconfig > @@ -221,6 +221,7 @@ 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 > + select NOMMU > default !MMU > > # set if we are running in S-mode and can use SBI calls > @@ -236,6 +237,13 @@ config MMU > Select if you want MMU-based virtualised addressing space > support by paged memory management. If unsure, say 'Y'. > > +config NOMMU > + depends on !MMU > + bool "NOMMU kernel (DEPRECATED)" > + help > + NOMMU kernel is deprecated and is scheduled for removal by > + the beginning of 2027. > + The idiomatic way to display this kind of warning is a comment directive: diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig index d4e890fb5b5a..b736440ce0f7 100644 --- a/arch/riscv/Kconfig +++ b/arch/riscv/Kconfig @@ -248,6 +248,9 @@ config MMU Select if you want MMU-based virtualised addressing space support by paged memory management. If unsure, say 'Y'. +comment "NOMMU support is deprecated (scheduled for removal in 2027)" + depends on !MMU + config PAGE_OFFSET hex default 0xC0000000 if 32BIT && MMU Regards, Samuel > config PAGE_OFFSET > hex > default 0xC0000000 if 32BIT && MMU > diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c > index 4f73c0ae44b2..8799816ef0a6 100644 > --- a/arch/riscv/kernel/setup.c > +++ b/arch/riscv/kernel/setup.c > @@ -295,6 +295,10 @@ void __init setup_arch(char **cmdline_p) > riscv_set_dma_cache_alignment(); > > riscv_user_isa_enable(); > + > +#if !defined(CONFIG_MMU) > + pr_err("RISC-V NOMMU support is deprecated and scheduled for removal by the beginning of 2027\n"); > +#endif > } > > bool arch_cpu_is_hotpluggable(int cpu)