On Mon, Mar 18, 2024 at 03:16:02PM +0000, Conor Dooley wrote:
From: Conor Dooley conor.dooley@microchip.com
cpu_get_desc() for the RISC-V CPU currently reads "riscv,isa" to get the description, but it is no longer a required property and cannot be assummed to always be present, as the new "riscv,isa-extensions" and "riscv,isa-base" properties may be present instead.
On RISC-V, cpu_get_desc() has two main uses - firstly providing an informational name for the CPU for smbios or at boot with DISPLAY_CPUINFO etc and secondly it forms the basis of ISA extension detection in supports_extension() as it returns (a portion of) an ISA string.
cpu_get_desc() returns a string, which aligned with "riscv,isa" but the new property is a list of strings. Rather than add support for the list of strings property, which would require creating an isa string from "riscv,isa-extensions", modify the RISC-V CPU's implementaion of cpu_get_desc() return the first compatible as the cpu description instead. This may be fine for the informational cases, but it would break extension dtection, given supports_extension() expects cpu_get_desc() to return an ISA string.
Call dev_read_string() directly in supports_extension() to get the contents of "riscv,isa" so that extension detection remains functional. As a knock-on affect of this change, extension detection is no longer broken for long ISA strings. Previously if the ISA string exceeded the 32 element array that supports_extension() passed to cpu_get_desc(), it would return ENOSPC and no extensions would be detected. This bug probably had no impact as U-Boot does not currently do anything meaningful with the results of supports_extension() and most SoCs supported by U-Boot don't have anywhere near that complex of an ISA string. The QEMU virt machine's CPUs do however, so extension detection doesn't work there.
Signed-off-by: Conor Dooley conor.dooley@microchip.com
I'm not really sure if I am happy with this patch - people could definitely have got use out of the cpu info printout of the ISA string before this patch - they'd have seen something like CPU: rv64imafdc at boot, but now they will see CPU: sifive,u74 If it really is desired, cpu_get_desc() could be made to assemble an isa string out of "riscv,isa-extensions", but I think it's always gonna be a bit flawed, since that string can run to almost arbitrary length now - one I saw for a CPU last week was 320 characters long and these things are only going to grow.
arch/riscv/cpu/cpu.c | 12 +++++++----- drivers/cpu/riscv_cpu.c | 8 ++++---- 2 files changed, 11 insertions(+), 9 deletions(-)
LGTM!
reviewed-by: Leo Yu-Chi Liang ycliang@andestech.com