6.6-stable review patch. If anyone has any objections, please let me know.
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From: Conor Dooley conor@kernel.org
[ Upstream commit d82f32202e0df7bf40d4b67c8a4ff9cea32df4d9 ]
Before attempting to support the pre-ratification version of vector found on older T-Head CPUs, disallow "v" in riscv,isa on these platforms. The deprecated property has no clear way to communicate the specific version of vector that is supported and much of the vendor provided software puts "v" in the isa string. riscv,isa-extensions should be used instead. This should not be too much of a burden for these systems, as the vendor shipped devicetrees and firmware do not work with a mainline kernel and will require updating.
We can limit this restriction to only ignore v in riscv,isa on CPUs that report T-Head's vendor ID and a zero marchid. Newer T-Head CPUs that support the ratified version of vector should report non-zero marchid, according to Guo Ren [1].
Link: https://lore.kernel.org/linux-riscv/CAJF2gTRy5eK73=d6s7CVy9m9pB8p4rAoMHM3cZF... [1] Fixes: dc6667a4e7e3 ("riscv: Extending cpufeature.c to detect V-extension") Co-developed-by: Conor Dooley conor.dooley@microchip.com Signed-off-by: Conor Dooley conor.dooley@microchip.com Acked-by: Guo Ren guoren@kernel.org Link: https://lore.kernel.org/r/20240223-tidings-shabby-607f086cb4d7@spud Signed-off-by: Palmer Dabbelt palmer@rivosinc.com Signed-off-by: Sasha Levin sashal@kernel.org --- arch/riscv/kernel/cpufeature.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+)
diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c index e12cd22755c78..e39a905aca248 100644 --- a/arch/riscv/kernel/cpufeature.c +++ b/arch/riscv/kernel/cpufeature.c @@ -21,6 +21,7 @@ #include <asm/hwprobe.h> #include <asm/patch.h> #include <asm/processor.h> +#include <asm/sbi.h> #include <asm/vector.h>
#include "copy-unaligned.h" @@ -396,6 +397,20 @@ static void __init riscv_fill_hwcap_from_isa_string(unsigned long *isa2hwcap) set_bit(RISCV_ISA_EXT_ZIHPM, isainfo->isa); }
+ /* + * "V" in ISA strings is ambiguous in practice: it should mean + * just the standard V-1.0 but vendors aren't well behaved. + * Many vendors with T-Head CPU cores which implement the 0.7.1 + * version of the vector specification put "v" into their DTs. + * CPU cores with the ratified spec will contain non-zero + * marchid. + */ + if (acpi_disabled && riscv_cached_mvendorid(cpu) == THEAD_VENDOR_ID && + riscv_cached_marchid(cpu) == 0x0) { + this_hwcap &= ~isa2hwcap[RISCV_ISA_EXT_v]; + clear_bit(RISCV_ISA_EXT_v, isainfo->isa); + } + /* * All "okay" hart should have same isa. Set HWCAP based on * common capabilities of every "okay" hart, in case they don't