[PATCH v4 0/2] riscv: Extension parsing fixes

[Charlie Jenkins]

This series contains two minor fixes for the extension parsing in
cpufeature.c.

Some T-Head boards without vector 1.0 support report "v" in the isa
string in their DT which will cause the kernel to run vector code. The
code to blacklist "v" from these boards was doing so by using
riscv_cached_mvendorid() which has not been populated at the time of
extension parsing. This fix instead greedily reads the mvendorid CSR of
the boot hart to determine if the cpu is from T-Head.

The other fix is for an incorrect indexing bug. riscv extensions
sometimes imply other extensions. When adding these "subset" extensions
to the hardware capabilities array, they need to be checked if they are
valid. The current code only checks if the extension that is including
other extensions is valid and not the subset extensions.  

These patches were previously included in:
https://lore.kernel.org/lkml/20240420-dev-charlie-support_thead_vector_6_9-v3-0-67cff4271d1d@rivosinc.com/

Signed-off-by: Charlie Jenkins <charlie at rivosinc.com>
---
Changes in v4:
- Delete comment
- Link to v3: https://lore.kernel.org/r/20240429-cpufeature_fixes-v3-0-6aa11dde513b@rivosinc.com

Changes in v3:
- Change comment about assuming all harts have the same vendorid/archid,
  to just state that only the boot hart is probed.
- Link to v2: https://lore.kernel.org/r/20240426-cpufeature_fixes-v2-0-7377442b1327@rivosinc.com

Changes in v2:
- Move comment about assuming all harts to have the same vendorid/archid
  to apply specifically to the code that expects that (Drew)
- Link to v1: https://lore.kernel.org/r/20240424-cpufeature_fixes-v1-0-585e73d2226b@rivosinc.com

---
Charlie Jenkins (2):
      riscv: cpufeature: Fix thead vector hwcap removal
      riscv: cpufeature: Fix extension subset checking

 arch/riscv/include/asm/sbi.h   |  2 ++
 arch/riscv/kernel/cpu.c        | 40 ++++++++++++++++++++++++++++++++++++----
 arch/riscv/kernel/cpufeature.c | 10 +++++++---
 3 files changed, 45 insertions(+), 7 deletions(-)
---
base-commit: ed30a4a51bb196781c8058073ea720133a65596f
change-id: 20240424-cpufeature_fixes-91bec4d793e7
-- 
- Charlie