[RFC PATCH 1/3] riscv: sbi: Add FWFT get helper

[Xie Bo]

The SBI FWFT extension supports querying a feature's value on the local
hart, but the RISC-V SBI wrapper currently only exposes SET operations.

Add a generic GET helper which maps SBI errors to Linux errno values and
only updates the caller's output on success.

Signed-off-by: Xie Bo <xb at ultrarisc.com>
---
 arch/riscv/include/asm/sbi.h |  1 +
 arch/riscv/kernel/sbi.c      | 29 +++++++++++++++++++++++++++++
 2 files changed, 30 insertions(+)

diff --git a/arch/riscv/include/asm/sbi.h b/arch/riscv/include/asm/sbi.h
index 5725e0c..b1773b1 100644
--- a/arch/riscv/include/asm/sbi.h
+++ b/arch/riscv/include/asm/sbi.h
@@ -607,6 +607,7 @@ int sbi_remote_hfence_vvma_asid(const struct cpumask *cpu_mask,
 				unsigned long asid);
 long sbi_probe_extension(int ext);
 
+int sbi_fwft_get(u32 feature, unsigned long *value);
 int sbi_fwft_set(u32 feature, unsigned long value, unsigned long flags);
 int sbi_fwft_set_cpumask(const cpumask_t *mask, u32 feature,
 			 unsigned long value, unsigned long flags);
diff --git a/arch/riscv/kernel/sbi.c b/arch/riscv/kernel/sbi.c
index c443337..51e0c58 100644
--- a/arch/riscv/kernel/sbi.c
+++ b/arch/riscv/kernel/sbi.c
@@ -318,6 +318,35 @@ static void cpu_sbi_fwft_set(void *arg)
 		atomic_set(&req->error, ret);
 }
 
+/**
+ * sbi_fwft_get() - Get a feature value on the local hart
+ * @feature: The feature ID to get
+ * @value: Where to store the feature value
+ *
+ * Return: 0 on success, appropriate Linux error code otherwise.
+ */
+int sbi_fwft_get(u32 feature, unsigned long *value)
+{
+	struct sbiret ret;
+	int error;
+
+	if (!sbi_fwft_supported)
+		return -EOPNOTSUPP;
+
+	if (!value)
+		return -EINVAL;
+
+	ret = sbi_ecall(SBI_EXT_FWFT, SBI_EXT_FWFT_GET,
+			feature, 0, 0, 0, 0, 0);
+	error = sbi_err_map_linux_errno(ret.error);
+	if (error)
+		return error;
+
+	*value = ret.value;
+
+	return 0;
+}
+
 /**
  * sbi_fwft_set() - Set a feature on the local hart
  * @feature: The feature ID to be set
-- 
2.17.1