timecounter: Merge FreeBSD change r282424

Implement a mechanism for making changes in the kernel<->driver PPS interface without breaking ABI or API compatibility with existing drivers.

The existing data structures used to communicate between the kernel and
driver portions of PPS processing contain no spare/padding fields and no
flags field or other straightforward mechanism for communicating changes
in the structures or behaviors of the code.  This makes it difficult to
MFC new features added to the PPS facility.  ABI compatibility is
important; out-of-tree drivers in module form are known to exist.  (Note
that the existing api_version field in the pps_params structure must
contain the value mandated by RFC 2783 and any RFCs that come along after.)

These changes introduce a pair of abi-version fields which are filled in
by the driver and the kernel respectively to indicate the interface
version.  The driver sets its version field before calling the new
pps_init_abi() function.  That lets the kernel know how much of the
pps_state structure is understood by the driver and it can avoid using
newer fields at the end of the structure that it knows about if the driver
is a lower version.  The kernel fills in its version field during the init
call, letting the driver know what features and data the kernel supports.

To implement the new version information in a way that is backwards
compatible with code from before these changes, the high bit of the
lightly-used 'kcmode' field is repurposed as a flag bit that indicates the
driver is aware of the abi versioning scheme.  Basically if this bit is
clear that indicates a "version 0" driver and if it is set the driver_abi
field indicates the version.

These changes also move the recently-added 'mtx' field of pps_state from
the middle to the end of the structure, and make the kernel code that uses
this field conditional on the driver being abi version 1 or higher.  It
changes the only driver currently supplying the mtx field, usb_serial, to
use pps_init_abi().

Reviewed by:	hselasky@

Update #3175.

2 files changed, 25 insertions, 6 deletions

diff --git a/cpukit/score/include/sys/timepps.h b/cpukit/score/include/sys/timepps.h
index 85bb6813cf..419e781be3 100644
--- a/cpukit/score/include/sys/timepps.h
+++ b/cpukit/score/include/sys/timepps.h
@@ -135,6 +135,13 @@ struct pps_kcbind_args {
 
 struct mtx;
 
+#define	KCMODE_EDGEMASK		0x03
+#define	KCMODE_ABIFLAG		0x80000000 /* Internal use: abi-aware driver. */
+
+#define	PPS_ABI_VERSION		1
+
+#define	PPSFLAG_MTX_SPIN	0x01	/* Driver mtx is MTX_SPIN type. */
+
 struct pps_state {
 	/* Capture information. */
 	struct timehands *capth;
@@ -142,9 +149,6 @@ struct pps_state {
 	unsigned	capgen;
 	unsigned	capcount;
 
-	/* pointer to mutex protecting this state, if any */
-	struct mtx	*mtx;
-
 	/* State information. */
 	pps_params_t	ppsparam;
 	pps_info_t	ppsinfo;
@@ -153,11 +157,19 @@ struct pps_state {
 	int		ppscap;
 	struct timecounter *ppstc;
 	unsigned	ppscount[3];
+	/*
+	 * The following fields are valid if the driver calls pps_init_abi().
+	 */
+	uint16_t	driver_abi;	/* Driver sets before pps_init_abi(). */
+	uint16_t	kernel_abi;	/* Kernel sets during pps_init_abi(). */
+	struct mtx	*driver_mtx;	/* Optional, valid if non-NULL. */
+	uint32_t	flags;
 };
 
 void pps_capture(struct pps_state *pps);
 void pps_event(struct pps_state *pps, int event);
 void pps_init(struct pps_state *pps);
+void pps_init_abi(struct pps_state *pps);
 int pps_ioctl(unsigned long cmd, caddr_t data, struct pps_state *pps);
 void hardpps(struct timespec *tsp, long nsec);
 
diff --git a/cpukit/score/src/kern_tc.c b/cpukit/score/src/kern_tc.c
index 0b27c8b68f..242983b464 100644
--- a/cpukit/score/src/kern_tc.c
+++ b/cpukit/score/src/kern_tc.c
@@ -1713,10 +1713,17 @@ pps_fetch(struct pps_fetch_args *fapi, struct pps_state *pps)
 		cseq = pps->ppsinfo.clear_sequence;
 		while (aseq == pps->ppsinfo.assert_sequence &&
 		    cseq == pps->ppsinfo.clear_sequence) {
-			if (pps->mtx != NULL)
-				err = msleep(pps, pps->mtx, PCATCH, "ppsfch", timo);
-			else
+			if (abi_aware(pps, 1) && pps->driver_mtx != NULL) {
+				if (pps->flags & PPSFLAG_MTX_SPIN) {
+					err = msleep_spin(pps, pps->driver_mtx,
+					    "ppsfch", timo);
+				} else {
+					err = msleep(pps, pps->driver_mtx, PCATCH,
+					    "ppsfch", timo);
+				}
+			} else {
 				err = tsleep(pps, PCATCH, "ppsfch", timo);
+			}
 			if (err == EWOULDBLOCK && fapi->timeout.tv_sec == -1) {
 				continue;
 			} else if (err != 0) {