[RFC PATCH 3/9] lib:sbi: Detect SSCOF extension at run time

[Atish Patra]

SSCOF ISA extension introduces PMU counter overflow and filtering support.
It introduces a read only `scountovf` csr that can be used to detect if
a hart supports this extension at runtime. However, this feature is only
useful if the hart already supports mcounteren and mcountinhibit.

Add a dynamic detection mechanism and boot time print message if sscof
is present.

Signed-off-by: Atish Patra <atish.patra at wdc.com>
---
 include/sbi/sbi_hart.h |  4 +++-
 lib/sbi/sbi_hart.c     | 12 ++++++++++++
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/include/sbi/sbi_hart.h b/include/sbi/sbi_hart.h
index 0c18ef9325b2..580a7989a4de 100644
--- a/include/sbi/sbi_hart.h
+++ b/include/sbi/sbi_hart.h
@@ -20,8 +20,10 @@ enum sbi_hart_features {
 	SBI_HART_HAS_MCOUNTEREN = (1 << 1),
 	/** Hart has counter inhibit CSR */
 	SBI_HART_HAS_MCOUNTINHIBIT = (1 << 2),
+	/** Hart has sscofpmf extension */
+	SBI_HART_HAS_SSCOF = (1 << 3),
 	/** HART has timer csr implementation in hardware */
-	SBI_HART_HAS_TIME = (1 << 3),
+	SBI_HART_HAS_TIME = (1 << 4),
 
 	/** Last index of Hart features*/
 	SBI_HART_HAS_LAST_FEATURE = SBI_HART_HAS_TIME,
diff --git a/lib/sbi/sbi_hart.c b/lib/sbi/sbi_hart.c
index 6254452e11bb..44b8dfd1b551 100644
--- a/lib/sbi/sbi_hart.c
+++ b/lib/sbi/sbi_hart.c
@@ -288,6 +288,9 @@ static inline char *sbi_hart_feature_id2string(unsigned long feature)
 	case SBI_HART_HAS_MCOUNTINHIBIT:
 		fstr = "mcountinhibit";
 		break;
+	case SBI_HART_HAS_SSCOF:
+		fstr = "sscof";
+		break;
 	case SBI_HART_HAS_TIME:
 		fstr = "time";
 		break;
@@ -497,6 +500,15 @@ __mhpm_skip:
 			hfeatures->features |= SBI_HART_HAS_MCOUNTINHIBIT;
 	}
 
+	/* Counter overflow/filtering is not useful without mcounter/inhibit */
+	if (hfeatures->features & SBI_HART_HAS_MCOUNTINHIBIT &&
+	    hfeatures->features & SBI_HART_HAS_MCOUNTEREN) {
+		/* Detect if hart supports sscofpmf */
+		csr_read_allowed(CSR_SCOUNTOVF, (unsigned long)&trap);
+		if (!trap.cause)
+			hfeatures->features |= SBI_HART_HAS_SSCOF;
+	}
+
 	/* Detect if hart supports time CSR */
 	csr_read_allowed(CSR_TIME, (unsigned long)&trap);
 	if (!trap.cause)
-- 
2.31.1