From 3b1526ddb25452385b52f2588b655f524a57070b Mon Sep 17 00:00:00 2001 From: Babis Chalios Date: Fri, 30 Jan 2026 17:36:01 +0000 Subject: ptp: vmclock: support device notifications Add optional support for device notifications in VMClock. When supported, the hypervisor will send a device notification every time it updates the seq_count to a new even value. Moreover, add support for poll() in VMClock as a means to propagate this notification to user space. poll() will return a POLLIN event to listeners every time seq_count changes to a value different than the one last seen (since open() or last read()/pread()). This means that when poll() returns a POLLIN event, listeners need to use read() to observe what has changed and update the reader's view of seq_count. In other words, after a poll() returned, all subsequent calls to poll() will immediately return with a POLLIN event until the listener calls read(). The device advertises support for the notification mechanism by setting flag VMCLOCK_FLAG_NOTIFICATION_PRESENT in vmclock_abi flags field. If the flag is not present the driver won't setup the ACPI notification handler and poll() will always immediately return POLLHUP. Signed-off-by: Babis Chalios Signed-off-by: David Woodhouse Signed-off-by: Takahiro Itazuri Reviewed-by: David Woodhouse Tested-by: Takahiro Itazuri Link: https://patch.msgid.link/20260130173704.12575-3-itazur@amazon.com Signed-off-by: Jakub Kicinski --- include/uapi/linux/vmclock-abi.h | 5 +++++ 1 file changed, 5 insertions(+) (limited to 'include/uapi/linux') diff --git a/include/uapi/linux/vmclock-abi.h b/include/uapi/linux/vmclock-abi.h index 937fe00e4f33..d320623b0118 100644 --- a/include/uapi/linux/vmclock-abi.h +++ b/include/uapi/linux/vmclock-abi.h @@ -121,6 +121,11 @@ struct vmclock_abi { * loaded from some save state (restored from a snapshot). */ #define VMCLOCK_FLAG_VM_GEN_COUNTER_PRESENT (1 << 8) + /* + * If the NOTIFICATION_PRESENT flag is set, the hypervisor will send + * a notification every time it updates seq_count to a new even number. + */ +#define VMCLOCK_FLAG_NOTIFICATION_PRESENT (1 << 9) __u8 pad[2]; __u8 clock_status; -- cgit v1.2.3