git: 0efa0fe26b9d - main - arm: Use the Self-Synchronized counter registers

The branch main has been updated by andrew:

URL: https://cgit.FreeBSD.org/src/commit/?id=0efa0fe26b9d980b2862bb58f8484f0123cff19f

commit 0efa0fe26b9d980b2862bb58f8484f0123cff19f
Author:     Andrew Turner <andrew@FreeBSD.org>
AuthorDate: 2025-09-22 17:08:47 +0000
Commit:     Andrew Turner <andrew@FreeBSD.org>
CommitDate: 2025-09-23 17:08:37 +0000

    arm: Use the Self-Synchronized counter registers
    
    When FEAT_ECV is implemented on arm64 a Self-Synchronized view of the
    counter registers are available. These don't need an isb before reading
    the count as they are not able to be speculatively executed.
    
    Sponsored by:   Arm Ltd
    Differential Revision:  https://reviews.freebsd.org/D51820
---
 sys/arm/arm/generic_timer.c | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/sys/arm/arm/generic_timer.c b/sys/arm/arm/generic_timer.c
index c4a1f44a0079..e3ba56a6f6ac 100644
--- a/sys/arm/arm/generic_timer.c
+++ b/sys/arm/arm/generic_timer.c
@@ -231,6 +231,25 @@ get_cntxct(bool physical)
 	return (val);
 }
 
+#ifdef __aarch64__
+/*
+ * Read the self-syncronized counter. These cannot be read speculatively so
+ * don't need an isb before them.
+ */
+static uint64_t
+get_cntxctss(bool physical)
+{
+	uint64_t val;
+
+	if (physical)
+		val = READ_SPECIALREG(CNTPCTSS_EL0_REG);
+	else
+		val = READ_SPECIALREG(CNTVCTSS_EL0_REG);
+
+	return (val);
+}
+#endif
+
 static int
 set_ctrl(uint32_t val, bool physical)
 {
@@ -631,6 +650,7 @@ arm_tmr_attach(device_t dev)
 	pcell_t clock;
 #endif
 #ifdef __aarch64__
+	uint64_t id_aa64mmfr0_el1;
 	int user_phys;
 #endif
 	int error;
@@ -641,6 +661,11 @@ arm_tmr_attach(device_t dev)
 		return (ENXIO);
 
 	sc->get_cntxct = &get_cntxct;
+#ifdef __aarch64__
+	if (get_kernel_reg(ID_AA64MMFR0_EL1, &id_aa64mmfr0_el1) &&
+	    ID_AA64MMFR0_ECV_VAL(id_aa64mmfr0_el1) >= ID_AA64MMFR0_ECV_IMPL)
+		sc->get_cntxct = &get_cntxctss;
+#endif
 #ifdef FDT
 	/* Get the base clock frequency */
 	node = ofw_bus_get_node(dev);