[PATCH v4 05/15] lib: sbi: Disable m/scounteren & enable mcountinhibit

[Atish Patra]

Currently, all bits in mcountern are enabled unconditionally at
boot time. With SBI PMU extension, all the programmable counters should enabled
only during performance monitoring for a particular event. However,
this is done only if mcountinhibit is implemented because the supervisor
mode can not start/stop any event without mcountinhibit.

Similarly, supervisor should take care enabling scounteren which allows
U-mode to access programmable pmu counters. All the non-programmable ones
(CY, TM, IR) should be enabled in M-mode because some userspace may rely on
builtins such as __builtin_readcyclecounter. Supervisor OS can still disable
them during initial configuration.

Reviewed-by: Anup Patel <anup.patel at wdc.com>
Signed-off-by: Atish Patra <atish.patra at wdc.com>
---
 lib/sbi/sbi_hart.c | 25 +++++++++++++++++++++----
 1 file changed, 21 insertions(+), 4 deletions(-)

diff --git a/lib/sbi/sbi_hart.c b/lib/sbi/sbi_hart.c
index e8cd0421b5e6..6254452e11bb 100644
--- a/lib/sbi/sbi_hart.c
+++ b/lib/sbi/sbi_hart.c
@@ -51,12 +51,29 @@ static void mstatus_init(struct sbi_scratch *scratch)
 
 	csr_write(CSR_MSTATUS, mstatus_val);
 
-	/* Enable user/supervisor use of perf counters */
+	/* Disable user mode usage of all perf counters except default ones (CY, TM, IR) */
 	if (misa_extension('S') &&
 	    sbi_hart_has_feature(scratch, SBI_HART_HAS_SCOUNTEREN))
-		csr_write(CSR_SCOUNTEREN, -1);
-	if (sbi_hart_has_feature(scratch, SBI_HART_HAS_MCOUNTEREN))
-		csr_write(CSR_MCOUNTEREN, -1);
+		csr_write(CSR_SCOUNTEREN, 7);
+
+	if (sbi_hart_has_feature(scratch, SBI_HART_HAS_MCOUNTEREN)) {
+		if (sbi_hart_has_feature(scratch, SBI_HART_HAS_MCOUNTINHIBIT))
+			/**
+			 * Just enable the default counters (CY, TM, IR) because
+			 * some OS (e.g FreeBSD) expect them to be enabled.
+			 *
+			 * All other counters will be enabled at runtime after
+			 * S-mode request.
+			 */
+			csr_write(CSR_MCOUNTEREN, 7);
+		else
+			/* Supervisor mode usage are enabled by default */
+			csr_write(CSR_MCOUNTEREN, -1);
+	}
+
+	/* All programmable counters will start running at runtime after S-mode request */
+	if (sbi_hart_has_feature(scratch, SBI_HART_HAS_MCOUNTINHIBIT))
+		csr_write(CSR_MCOUNTINHIBIT, 0xFFFFFFF8);
 
 	/* Disable all interrupts */
 	csr_write(CSR_MIE, 0);
-- 
2.31.1