virtio_rtc: Add Arm Generic Timer cross-timestamping

For platforms using the Arm Generic Timer, add precise cross-timestamping
support to virtio_rtc.

Always report the CP15 virtual counter as the HW counter in use by
arm_arch_timer, since the Linux kernel's usage of the Arm Generic Timer
should always be compatible with this.

Signed-off-by: Peter Hilber <quic_philber@quicinc.com>
Message-Id: <20250509160734.1772-4-quic_philber@quicinc.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

diff --git a/drivers/virtio/Kconfig b/drivers/virtio/Kconfig
index a14a2b7..3d8b366 100644 (file)
--- a/drivers/virtio/Kconfig
+++ b/drivers/virtio/Kconfig
@@ -221,6 +221,19 @@ config VIRTIO_RTC_PTP
 
         If unsure, say Y.
 
+config VIRTIO_RTC_ARM
+       bool "Virtio RTC cross-timestamping using Arm Generic Timer"
+       default y
+       depends on VIRTIO_RTC_PTP && ARM_ARCH_TIMER
+       help
+        This enables Virtio RTC cross-timestamping using the Arm Generic Timer.
+        It only has an effect if the Virtio RTC device also supports this. The
+        cross-timestamp is available through the PTP clock driver precise
+        cross-timestamp ioctl (PTP_SYS_OFFSET_PRECISE2 aka
+        PTP_SYS_OFFSET_PRECISE).
+
+        If unsure, say Y.
+
 endif # VIRTIO_RTC
 
 endif # VIRTIO_MENU

diff --git a/drivers/virtio/Makefile b/drivers/virtio/Makefile
index 88d6fb8..dbd77f1 100644 (file)
--- a/drivers/virtio/Makefile
+++ b/drivers/virtio/Makefile
@@ -17,3 +17,4 @@ obj-$(CONFIG_VIRTIO_DEBUG) += virtio_debug.o
 obj-$(CONFIG_VIRTIO_RTC) += virtio_rtc.o
 virtio_rtc-y := virtio_rtc_driver.o
 virtio_rtc-$(CONFIG_VIRTIO_RTC_PTP) += virtio_rtc_ptp.o
+virtio_rtc-$(CONFIG_VIRTIO_RTC_ARM) += virtio_rtc_arm.o

diff --git a/drivers/virtio/virtio_rtc_arm.c b/drivers/virtio/virtio_rtc_arm.c
new file mode 100644 (file)
index 0000000..211299d
--- /dev/null
+++ b/drivers/virtio/virtio_rtc_arm.c
@@ -0,0 +1,23 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Provides cross-timestamp params for Arm.
+ *
+ * Copyright (C) 2022-2023 OpenSynergy GmbH
+ * Copyright (c) 2024 Qualcomm Innovation Center, Inc. All rights reserved.
+ */
+
+#include <linux/clocksource_ids.h>
+
+#include <uapi/linux/virtio_rtc.h>
+
+#include "virtio_rtc_internal.h"
+
+/* see header for doc */
+
+int viortc_hw_xtstamp_params(u8 *hw_counter, enum clocksource_ids *cs_id)
+{
+       *hw_counter = VIRTIO_RTC_COUNTER_ARM_VCT;
+       *cs_id = CSID_ARM_ARCH_COUNTER;
+
+       return 0;
+}