[PATCH v9 05/13] riscv: vector: Use vlenb from DT for thead

Charlie Jenkins
2024-08-07T00:32:00Z

If thead,vlenb is provided in the device tree, prefer that over reading
the vlenb csr.

Signed-off-by: Charlie Jenkins <charlie@rivosinc.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
---
arch/riscv/Kconfig.vendor | 13 ++++++++++
arch/riscv/include/asm/cpufeature.h | 2 ++
arch/riscv/kernel/cpufeature.c | 48 +++++++++++++++++++++++++++++++++++++
arch/riscv/kernel/vector.c | 12 +++++++++-
4 files changed, 74 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/Kconfig.vendor b/arch/riscv/Kconfig.vendor
index 9897442bd44f..b096548fe0ff 100644
--- a/arch/riscv/Kconfig.vendor
+++ b/arch/riscv/Kconfig.vendor
@@ -26,6 +26,19 @@ config RISCV_ISA_VENDOR_EXT_THEAD
extensions. Without this option enabled, T-Head vendor extensions will
not be detected at boot and their presence not reported to userspace.

+ If you don't know what to do here, say Y.
+
+config RISCV_ISA_XTHEADVECTOR
+ bool "xtheadvector extension support"
+ depends on RISCV_ISA_VENDOR_EXT_THEAD
+ depends on RISCV_ISA_V
+ depends on FPU
+ default y
+ help
+ Say N here if you want to disable all xtheadvector related procedures
+ in the kernel. This will disable vector for any T-Head board that
+ contains xtheadvector rather than the standard vector.
+
If you don't know what to do here, say Y.
endmenu

diff --git a/arch/riscv/include/asm/cpufeature.h b/arch/riscv/include/asm/cpufeature.h
index 45f9c1171a48..28bdeb1005e0 100644
--- a/arch/riscv/include/asm/cpufeature.h
+++ b/arch/riscv/include/asm/cpufeature.h
@@ -31,6 +31,8 @@ DECLARE_PER_CPU(struct riscv_cpuinfo, riscv_cpuinfo);
/* Per-cpu ISA extensions. */
extern struct riscv_isainfo hart_isa[NR_CPUS];

+extern u32 thead_vlenb_of;
+
void riscv_user_isa_enable(void);

#define _RISCV_ISA_EXT_DATA(_name, _id, _subset_exts, _subset_exts_size, _validate) { \
diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
index 46e69b9d66a7..477375e5edb0 100644
--- a/arch/riscv/kernel/cpufeature.c
+++ b/arch/riscv/kernel/cpufeature.c
@@ -37,6 +37,8 @@ static DECLARE_BITMAP(riscv_isa, RISCV_ISA_EXT_MAX) __read_mostly;
/* Per-cpu ISA extensions. */
struct riscv_isainfo hart_isa[NR_CPUS];

+u32 thead_vlenb_of;
+
/**
* riscv_isa_extension_base() - Get base extension word
*
@@ -772,6 +774,46 @@ static void __init riscv_fill_vendor_ext_list(int cpu)
}
}

+static int has_thead_homogeneous_vlenb(void)
+{
+ int cpu;
+ u32 prev_vlenb = 0;
+ u32 vlenb;
+
+ /* Ignore thead,vlenb property if xtheavector is not enabled in the kernel */
+ if (!IS_ENABLED(CONFIG_RISCV_ISA_XTHEADVECTOR))
+ return 0;
+
+ for_each_possible_cpu(cpu) {
+ struct device_node *cpu_node;
+
+ cpu_node = of_cpu_device_node_get(cpu);
+ if (!cpu_node) {
+ pr_warn("Unable to find cpu node\n");
+ return -ENOENT;
+ }
+
+ if (of_property_read_u32(cpu_node, "thead,vlenb", &vlenb)) {
+ of_node_put(cpu_node);
+
+ if (prev_vlenb)
+ return -ENOENT;
+ continue;
+ }
+
+ if (prev_vlenb && vlenb != prev_vlenb) {
+ of_node_put(cpu_node);
+ return -ENOENT;
+ }
+
+ prev_vlenb = vlenb;
+ of_node_put(cpu_node);
+ }
+
+ thead_vlenb_of = vlenb;
+ return 0;
+}
+
static int __init riscv_fill_hwcap_from_ext_list(unsigned long *isa2hwcap)
{
unsigned int cpu;
@@ -825,6 +867,12 @@ static int __init riscv_fill_hwcap_from_ext_list(unsigned long *isa2hwcap)
riscv_fill_vendor_ext_list(cpu);
}

+ if (riscv_isa_vendor_extension_available(THEAD_VENDOR_ID, XTHEADVECTOR) &&
+ has_thead_homogeneous_vlenb() < 0) {
+ pr_warn("Unsupported heterogeneous vlenb detected, vector extension disabled.\n");
+ elf_hwcap &= ~COMPAT_HWCAP_ISA_V;
+ }
+
if (bitmap_empty(riscv_isa, RISCV_ISA_EXT_MAX))
return -ENOENT;

diff --git a/arch/riscv/kernel/vector.c b/arch/riscv/kernel/vector.c
index 682b3feee451..9775d6a9c8ee 100644
--- a/arch/riscv/kernel/vector.c
+++ b/arch/riscv/kernel/vector.c
@@ -33,7 +33,17 @@ int riscv_v_setup_vsize(void)
{
unsigned long this_vsize;

- /* There are 32 vector registers with vlenb length. */
+ /*
+ * There are 32 vector registers with vlenb length.
+ *
+ * If the thead,vlenb property was provided by the firmware, use that
+ * instead of probing the CSRs.
+ */
+ if (thead_vlenb_of) {
+ this_vsize = thead_vlenb_of * 32;
+ return 0;
+ }
+
riscv_v_enable();
this_vsize = csr_read(CSR_VLENB) * 32;
riscv_v_disable();