[PATCH v3 1/2] lib: sbi: hart: Detect existence of cycle and instret CSRs for Zicntr

[Yao Zi]

Zicntr extension specifies three read-only CSRs, time, cycle and
instret. It isn't sufficient to report Zicntr is fully supported with
only time CSR detected.

This patch introduces a bitmap to sbi_hart_features to record
availability of these CSRs, which are detected using traps. Zicntr is
reported as present if and only if three CSRs are all available on the
HARTs.

Suggested-by: Anup Patel <anup at brainfault.org>
Signed-off-by: Yao Zi <ziyao at disroot.org>
---
 include/sbi/sbi_hart.h | 10 ++++++++++
 lib/sbi/sbi_hart.c     | 35 ++++++++++++++++++++++++++++-------
 2 files changed, 38 insertions(+), 7 deletions(-)

diff --git a/include/sbi/sbi_hart.h b/include/sbi/sbi_hart.h
index bce88c5..dfbe8e4 100644
--- a/include/sbi/sbi_hart.h
+++ b/include/sbi/sbi_hart.h
@@ -93,6 +93,14 @@ struct sbi_hart_ext_data {
 
 extern const struct sbi_hart_ext_data sbi_hart_ext[];
 
+/** CSRs should be detected by access and trapping */
+enum sbi_hart_csrs {
+	SBI_HART_CSR_CYCLE = 0,
+	SBI_HART_CSR_TIME,
+	SBI_HART_CSR_INSTRET,
+	SBI_HART_CSR_MAX,
+};
+
 /*
  * Smepmp enforces access boundaries between M-mode and
  * S/U-mode. When it is enabled, the PMPs are programmed
@@ -112,6 +120,7 @@ struct sbi_hart_features {
 	bool detected;
 	int priv_version;
 	unsigned long extensions[BITS_TO_LONGS(SBI_HART_EXT_MAX)];
+	unsigned long csrs[BITS_TO_LONGS(SBI_HART_CSR_MAX)];
 	unsigned int pmp_count;
 	unsigned int pmp_addr_bits;
 	unsigned int pmp_log2gran;
@@ -150,6 +159,7 @@ bool sbi_hart_has_extension(struct sbi_scratch *scratch,
 			    enum sbi_hart_extensions ext);
 void sbi_hart_get_extensions_str(struct sbi_scratch *scratch,
 				 char *extension_str, int nestr);
+bool sbi_hart_has_csr(struct sbi_scratch *scratch, enum sbi_hart_csrs csr);
 
 void __attribute__((noreturn)) sbi_hart_hang(void);
 
diff --git a/lib/sbi/sbi_hart.c b/lib/sbi/sbi_hart.c
index fc4925b..74ccdd8 100644
--- a/lib/sbi/sbi_hart.c
+++ b/lib/sbi/sbi_hart.c
@@ -747,6 +747,20 @@ void sbi_hart_get_extensions_str(struct sbi_scratch *scratch,
 		sbi_strncpy(extensions_str, "none", nestr);
 }
 
+/**
+ * Check whether a particular CSR is present on the HART
+ *
+ * @param scratch pointer to the HART scratch space
+ * @param csr the CSR number to check
+ */
+bool sbi_hart_has_csr(struct sbi_scratch *scratch, enum sbi_hart_csrs csr)
+{
+	struct sbi_hart_features *hfeatures =
+			sbi_scratch_offset_ptr(scratch, hart_features_offset);
+
+	return __test_bit(csr, hfeatures->csrs);
+}
+
 static unsigned long hart_pmp_get_allowed_addr(void)
 {
 	unsigned long val = 0;
@@ -803,7 +817,6 @@ static int hart_detect_features(struct sbi_scratch *scratch)
 	struct sbi_hart_features *hfeatures =
 		sbi_scratch_offset_ptr(scratch, hart_features_offset);
 	unsigned long val, oldval;
-	bool has_zicntr = false;
 	int rc;
 
 	/* If hart features already detected then do nothing */
@@ -812,6 +825,7 @@ static int hart_detect_features(struct sbi_scratch *scratch)
 
 	/* Clear hart features */
 	sbi_memset(hfeatures->extensions, 0, sizeof(hfeatures->extensions));
+	sbi_memset(hfeatures->csrs, 0, sizeof(hfeatures->csrs));
 	hfeatures->pmp_count = 0;
 	hfeatures->mhpm_mask = 0;
 	hfeatures->priv_version = SBI_HART_PRIV_VER_UNKNOWN;
@@ -938,9 +952,6 @@ __pmp_skip:
 	/* Detect if hart supports sscofpmf */
 	__check_ext_csr(SBI_HART_PRIV_VER_1_11,
 			CSR_SCOUNTOVF, SBI_HART_EXT_SSCOFPMF);
-	/* Detect if hart supports time CSR */
-	__check_ext_csr(SBI_HART_PRIV_VER_UNKNOWN,
-			CSR_TIME, SBI_HART_EXT_ZICNTR);
 	/* Detect if hart has AIA local interrupt CSRs */
 	__check_ext_csr(SBI_HART_PRIV_VER_UNKNOWN,
 			CSR_MTOPI, SBI_HART_EXT_SMAIA);
@@ -962,8 +973,16 @@ __pmp_skip:
 
 #undef __check_ext_csr
 
-	/* Save trap based detection of Zicntr */
-	has_zicntr = sbi_hart_has_extension(scratch, SBI_HART_EXT_ZICNTR);
+#define __check_csr_existence(__csr, __csr_id)				\
+	csr_read_allowed(__csr, &trap);					\
+	if (!trap.cause)						\
+		__set_bit(__csr_id, hfeatures->csrs);
+
+	__check_csr_existence(CSR_CYCLE, SBI_HART_CSR_CYCLE);
+	__check_csr_existence(CSR_TIME, SBI_HART_CSR_TIME);
+	__check_csr_existence(CSR_INSTRET, SBI_HART_CSR_INSTRET);
+
+#undef __check_csr_existence
 
 	/* Let platform populate extensions */
 	rc = sbi_platform_extensions_init(sbi_platform_thishart_ptr(),
@@ -973,7 +992,9 @@ __pmp_skip:
 
 	/* Zicntr should only be detected using traps */
 	__sbi_hart_update_extension(hfeatures, SBI_HART_EXT_ZICNTR,
-				    has_zicntr);
+			    sbi_hart_has_csr(scratch, SBI_HART_CSR_CYCLE) &&
+			    sbi_hart_has_csr(scratch, SBI_HART_CSR_TIME)  &&
+			    sbi_hart_has_csr(scratch, SBI_HART_CSR_INSTRET));
 
 	/* Extensions implied by other extensions and features */
 	if (hfeatures->mhpm_mask)
-- 
2.49.0