[PATCH v2 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 |  9 +++++++++
 lib/sbi/sbi_hart.c     | 35 ++++++++++++++++++++++++++++-------
 2 files changed, 37 insertions(+), 7 deletions(-)

diff --git a/include/sbi/sbi_hart.h b/include/sbi/sbi_hart.h
index c3a7feb..48edafe 100644
--- a/include/sbi/sbi_hart.h
+++ b/include/sbi/sbi_hart.h
@@ -91,6 +91,13 @@ 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,
+};
+
 /*
  * Smepmp enforces access boundaries between M-mode and
  * S/U-mode. When it is enabled, the PMPs are programmed
@@ -110,6 +117,7 @@ struct sbi_hart_features {
 	bool detected;
 	int priv_version;
 	unsigned long extensions[BITS_TO_LONGS(SBI_HART_EXT_MAX)];
+	unsigned long csrs;
 	unsigned int pmp_count;
 	unsigned int pmp_addr_bits;
 	unsigned int pmp_log2gran;
@@ -148,6 +156,7 @@ 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 c343805..f98b6b0 100644
--- a/lib/sbi/sbi_hart.c
+++ b/lib/sbi/sbi_hart.c
@@ -733,6 +733,20 @@ 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 (hfeatures->csrs >> csr) & 1UL;
+}
+
 static unsigned long hart_pmp_get_allowed_addr(void)
 {
 	unsigned long val = 0;
@@ -789,7 +803,6 @@ 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 */
@@ -798,6 +811,7 @@ static int hart_detect_features(struct sbi_scratch *scratch)
 
 	/* Clear hart features */
 	sbi_memset(hfeatures->extensions, 0, sizeof(hfeatures->extensions));
+	hfeatures->csrs = 0;
 	hfeatures->pmp_count = 0;
 	hfeatures->mhpm_mask = 0;
 	hfeatures->priv_version = SBI_HART_PRIV_VER_UNKNOWN;
@@ -924,9 +938,6 @@ __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);
@@ -945,8 +956,16 @@ __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)						\
+		hfeatures->csrs |= 1 << __csr_id;
+
+	__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(),
@@ -956,7 +975,9 @@ __pmp_skip:
 
 	/* Zicntr should only be detected using traps */
 	__sbi_hart_update_extension(hfeatures, SBI_HART_EXT_ZICNTR,
-				    has_zicntr);
+			    (hfeatures->csrs & BIT(SBI_HART_CSR_CYCLE))	&&
+			    (hfeatures->csrs & BIT(SBI_HART_CSR_TIME))	&&
+			    (hfeatures->csrs & BIT(SBI_HART_CSR_INSTRET)));
 
 	/* Extensions implied by other extensions and features */
 	if (hfeatures->mhpm_mask)
-- 
2.49.0