[PATCH] lib: sbi: Ensure SBI extension is available

[Andrew Jones <ajones@ventanamicro.com>]

Ensure attempts to invoke SBI extension functions fail with
SBI_ERR_NOT_SUPPORTED when the extension's probe function has
reported that the extension is not available. By adding a new
status member to the extension which has three states
(uninitialized, available, unavailable), we ensure that the
probe function is only invoked once, lazily, upon first use.

Signed-off-by: Andrew Jones <ajones@ventanamicro.com>
---
 include/sbi/sbi_ecall.h |  6 ++++++
 lib/sbi/sbi_ecall.c     | 18 ++++++++++++++----
 2 files changed, 20 insertions(+), 4 deletions(-)

diff --git a/include/sbi/sbi_ecall.h b/include/sbi/sbi_ecall.h
index ff9bf8e2b435..8e31d0d91620 100644
--- a/include/sbi/sbi_ecall.h
+++ b/include/sbi/sbi_ecall.h
@@ -20,10 +20,16 @@
 struct sbi_trap_regs;
 struct sbi_trap_info;
 
+enum sbi_ext_status {
+	SBI_EXT_AVAILABLE = 1,
+	SBI_EXT_UNAVAILABLE,
+};
+
 struct sbi_ecall_extension {
 	struct sbi_dlist head;
 	unsigned long extid_start;
 	unsigned long extid_end;
+	enum sbi_ext_status status;
 	int (* probe)(unsigned long extid, unsigned long *out_val);
 	int (* handle)(unsigned long extid, unsigned long funcid,
 		       const struct sbi_trap_regs *regs,
diff --git a/lib/sbi/sbi_ecall.c b/lib/sbi/sbi_ecall.c
index 76a1ae9ab733..20ff06f32dad 100644
--- a/lib/sbi/sbi_ecall.c
+++ b/lib/sbi/sbi_ecall.c
@@ -42,16 +42,26 @@ static SBI_LIST_HEAD(ecall_exts_list);
 
 struct sbi_ecall_extension *sbi_ecall_find_extension(unsigned long extid)
 {
-	struct sbi_ecall_extension *t, *ret = NULL;
+	struct sbi_ecall_extension *t;
+	unsigned long out_val;
 
 	sbi_list_for_each_entry(t, &ecall_exts_list, head) {
 		if (t->extid_start <= extid && extid <= t->extid_end) {
-			ret = t;
-			break;
+			if (t->status == SBI_EXT_AVAILABLE)
+				return t;
+			if (t->status == SBI_EXT_UNAVAILABLE)
+				return NULL;
+			if (t->probe && (t->probe(extid, &out_val) || !out_val)) {
+				t->status = SBI_EXT_UNAVAILABLE;
+				return NULL;
+			}
+
+			t->status = SBI_EXT_AVAILABLE;
+			return t;
 		}
 	}
 
-	return ret;
+	return NULL;
 }
 
 int sbi_ecall_register_extension(struct sbi_ecall_extension *ext)
-- 
2.39.2