From: Conor Dooley conor.dooley@microchip.com
[ Upstream commit 99e2266f2460e5778560f81982b6301dd2a16502 ]
While the current list of rules may have been accurate when created it now lacks some clarity in the face of isa-manual updates. Instead of trying to continuously align this rule-set with the one in the specifications, change the role of this comment.
This particular comment is important, as the array it "decorates" defines the order in which the ISA string appears to userspace in /proc/cpuinfo.
Re-jig and strengthen the wording to provide contributors with a set order in which to add entries & note why this particular struct needs more attention than others.
While in the area, add some whitespace and tweak some wording for readability's sake.
Suggested-by: Andrew Jones ajones@ventanamicro.com Reviewed-by: Andrew Jones ajones@ventanamicro.com Signed-off-by: Conor Dooley conor.dooley@microchip.com Link: https://lore.kernel.org/r/20221205144525.2148448-2-conor.dooley@microchip.co... Signed-off-by: Palmer Dabbelt palmer@rivosinc.com Stable-dep-of: 1eac28201ac0 ("RISC-V: fix ordering of Zbb extension") Signed-off-by: Sasha Levin sashal@kernel.org --- arch/riscv/kernel/cpu.c | 49 ++++++++++++++++++++++++++++++----------- 1 file changed, 36 insertions(+), 13 deletions(-)
diff --git a/arch/riscv/kernel/cpu.c b/arch/riscv/kernel/cpu.c index 1b9a5a66e55ab..db8b16ad9342b 100644 --- a/arch/riscv/kernel/cpu.c +++ b/arch/riscv/kernel/cpu.c @@ -144,22 +144,45 @@ arch_initcall(riscv_cpuinfo_init); .uprop = #UPROP, \ .isa_ext_id = EXTID, \ } + /* - * Here are the ordering rules of extension naming defined by RISC-V - * specification : - * 1. All extensions should be separated from other multi-letter extensions - * by an underscore. - * 2. The first letter following the 'Z' conventionally indicates the most + * The canonical order of ISA extension names in the ISA string is defined in + * chapter 27 of the unprivileged specification. + * + * Ordinarily, for in-kernel data structures, this order is unimportant but + * isa_ext_arr defines the order of the ISA string in /proc/cpuinfo. + * + * The specification uses vague wording, such as should, when it comes to + * ordering, so for our purposes the following rules apply: + * + * 1. All multi-letter extensions must be separated from other extensions by an + * underscore. + * + * 2. Additional standard extensions (starting with 'Z') must be sorted after + * single-letter extensions and before any higher-privileged extensions. + + * 3. The first letter following the 'Z' conventionally indicates the most * closely related alphabetical extension category, IMAFDQLCBKJTPVH. - * If multiple 'Z' extensions are named, they should be ordered first - * by category, then alphabetically within a category. - * 3. Standard supervisor-level extensions (starts with 'S') should be - * listed after standard unprivileged extensions. If multiple - * supervisor-level extensions are listed, they should be ordered + * If multiple 'Z' extensions are named, they must be ordered first by + * category, then alphabetically within a category. + * + * 3. Standard supervisor-level extensions (starting with 'S') must be listed + * after standard unprivileged extensions. If multiple supervisor-level + * extensions are listed, they must be ordered alphabetically. + * + * 4. Standard machine-level extensions (starting with 'Zxm') must be listed + * after any lower-privileged, standard extensions. If multiple + * machine-level extensions are listed, they must be ordered * alphabetically. - * 4. Non-standard extensions (starts with 'X') must be listed after all - * standard extensions. They must be separated from other multi-letter - * extensions by an underscore. + * + * 5. Non-standard extensions (starting with 'X') must be listed after all + * standard extensions. If multiple non-standard extensions are listed, they + * must be ordered alphabetically. + * + * An example string following the order is: + * rv64imadc_zifoo_zigoo_zafoo_sbar_scar_zxmbaz_xqux_xrux + * + * New entries to this struct should follow the ordering rules described above. */ static struct riscv_isa_ext_data isa_ext_arr[] = { __RISCV_ISA_EXT_DATA(sscofpmf, RISCV_ISA_EXT_SSCOFPMF),