riscv: don't read riscv, isa in the riscv cpu's get_desc()

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 <[email protected]>
reviewed-by: Leo Yu-Chi Liang <[email protected]>

1 files changed, 4 insertions, 4 deletions

diff --git a/drivers/cpu/riscv_cpu.c b/drivers/cpu/riscv_cpu.c
index 5d1026b37da..9b1950efe05 100644
--- a/drivers/cpu/riscv_cpu.c
+++ b/drivers/cpu/riscv_cpu.c
@@ -21,13 +21,13 @@ DECLARE_GLOBAL_DATA_PTR;
 
 static int riscv_cpu_get_desc(const struct udevice *dev, char *buf, int size)
 {
-	const char *isa;
+	const char *cpu;
 
-	isa = dev_read_string(dev, "riscv,isa");
-	if (size < (strlen(isa) + 1))
+	cpu = dev_read_string(dev, "compatible");
+	if (size < (strlen(cpu) + 1))
 		return -ENOSPC;
 
-	strcpy(buf, isa);
+	strcpy(buf, cpu);
 
 	return 0;
 }