[PATCH v3] lib: sbi: Ensure SBI extension is available

[Andrew Jones]

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. To avoid invoking
probe too frequently, we check single extension ID extensions at
init time and even drop them from the extension list when their
probe fails. If the probe succeeds, we keep it, and then later
seeing that it's a single extension ID extension is enough to know
it's available. Extensions which have multiple IDs must have its probe
called for each, so we don't try to reduce calls to those. It's
expected that these multi-ID extension probe functions implement
their own optimizations in order to ensure extension lookups are
fast.

Signed-off-by: Andrew Jones <ajones at ventanamicro.com>
---
v3:
 - Only apply optimization to single extension ID extensions [Xiang]
 - Drop extensions from extension list when they can be probed
   at init time (and drop the, now unnecessary, status) [Anup]

 lib/sbi/sbi_ecall.c | 32 +++++++++++++++++++++++---------
 1 file changed, 23 insertions(+), 9 deletions(-)

diff --git a/lib/sbi/sbi_ecall.c b/lib/sbi/sbi_ecall.c
index 76a1ae9ab733..cb73105d7aa8 100644
--- a/lib/sbi/sbi_ecall.c
+++ b/lib/sbi/sbi_ecall.c
@@ -42,16 +42,19 @@ 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->extid_start != t->extid_end && t->probe &&
+			    (t->probe(extid, &out_val) || !out_val))
+				return NULL;
+			return t;
 		}
 	}
 
-	return ret;
+	return NULL;
 }
 
 int sbi_ecall_register_extension(struct sbi_ecall_extension *ext)
@@ -148,15 +151,26 @@ int sbi_ecall_handler(struct sbi_trap_regs *regs)
 
 int sbi_ecall_init(void)
 {
-	int ret;
 	struct sbi_ecall_extension *ext;
-	unsigned long i;
+	unsigned long out_val, i;
+	int ret;
 
 	for (i = 0; i < sbi_ecall_exts_size; i++) {
 		ext = sbi_ecall_exts[i];
-		ret = sbi_ecall_register_extension(ext);
-		if (ret)
-			return ret;
+		/*
+		 * Don't bother adding extensions which have a single extension
+		 * ID and its probe fails. Extensions with multiple IDs need to
+		 * have their probe called on specific IDs, so we need to add
+		 * them here and probe on each use. And, of course, if there
+		 * isn't a probe function, then the extension is always
+		 * available, so we add it here.
+		 */
+		if (ext->extid_start != ext->extid_end || !ext->probe ||
+		    (!ext->probe(ext->extid_start, &out_val) && out_val)) {
+			ret = sbi_ecall_register_extension(ext);
+			if (ret)
+				return ret;
+		}
 	}
 
 	return 0;
-- 
2.40.0