LinuxKPI: Implement sequence counters and sequential locks

as a thin wrapper around native version found in sys/seqc.h.
This replaces out-of-base GPLv2-licensed code used by drm-kmod.

Reviewed by:	hselasky
Differential revision:	https://reviews.freebsd.org/D31006

(cherry picked from commit 8b33cb8303d3d7ff12e34327a872ef9fdb29eab9)

1 files changed, 137 insertions, 0 deletions

diff --git a/sys/compat/linuxkpi/common/include/linux/seqlock.h b/sys/compat/linuxkpi/common/include/linux/seqlock.h
new file mode 100644
index 000000000000..b7ae6e32ae69
--- /dev/null
+++ b/sys/compat/linuxkpi/common/include/linux/seqlock.h
@@ -0,0 +1,137 @@
+/*-
+ * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
+ *
+ * Copyright (c) 2021 Vladimir Kondratyev <wulf@FreeBSD.org>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#ifndef _LINUX_SEQLOCK_H__
+#define	_LINUX_SEQLOCK_H__
+
+#include <sys/param.h>
+#include <sys/lock.h>
+#include <sys/mutex.h>
+#include <sys/seqc.h>
+
+struct lock_class_key;
+
+struct seqcount {
+	seqc_t		seqc;
+};
+typedef struct seqcount seqcount_t;
+
+struct seqlock {
+	struct mtx	seql_lock;
+	struct seqcount	seql_count;
+};
+typedef struct seqlock seqlock_t;
+
+static inline void
+__seqcount_init(struct seqcount *seqcount, const char *name __unused,
+    struct lock_class_key *key __unused)
+{
+	seqcount->seqc = 0;
+}
+#define	seqcount_init(seqcount)	__seqcount_init(seqcount, NULL, NULL)
+
+static inline void
+write_seqcount_begin(struct seqcount *seqcount)
+{
+	seqc_sleepable_write_begin(&seqcount->seqc);
+}
+
+static inline void
+write_seqcount_end(struct seqcount *seqcount)
+{
+	seqc_sleepable_write_end(&seqcount->seqc);
+}
+
+/*
+ * XXX: Are predicts from inline functions still not honored by clang?
+ */
+#define	__read_seqcount_retry(seqcount, gen)	\
+	(!seqc_consistent_nomb(&(seqcount)->seqc, gen))
+#define	read_seqcount_retry(seqcount, gen)	\
+	(!seqc_consistent(&(seqcount)->seqc, gen))
+
+static inline unsigned
+read_seqcount_begin(const struct seqcount *seqcount)
+{
+	return (seqc_read(&seqcount->seqc));
+}
+
+static inline unsigned
+raw_read_seqcount(const struct seqcount *seqcount)
+{
+	return (seqc_read_any(&seqcount->seqc));
+}
+
+static inline void
+seqlock_init(struct seqlock *seqlock)
+{
+	/*
+	 * Don't enroll to witness(4) to avoid orphaned references after struct
+	 * seqlock has been freed. There is no seqlock destructor exists so we
+	 * can't expect automatic mtx_destroy() execution before free().
+	 */
+	mtx_init(&seqlock->seql_lock, "seqlock", NULL, MTX_DEF|MTX_NOWITNESS);
+	seqcount_init(&seqlock->seql_count);
+}
+
+static inline void
+write_seqlock(struct seqlock *seqlock)
+{
+	mtx_lock(&seqlock->seql_lock);
+	write_seqcount_begin(&seqlock->seql_count);
+}
+
+static inline void
+write_sequnlock(struct seqlock *seqlock)
+{
+	write_seqcount_end(&seqlock->seql_count);
+	mtx_unlock(&seqlock->seql_lock);
+}
+
+#define	write_seqlock_irqsave(seqlock, flags)	do {	\
+	(flags) = 0;					\
+	write_seqlock(seqlock);				\
+} while (0)
+
+static inline void
+write_sequnlock_irqrestore(struct seqlock *seqlock,
+    unsigned long flags __unused)
+{
+	write_sequnlock(seqlock);
+}
+
+static inline unsigned
+read_seqbegin(const struct seqlock *seqlock)
+{
+	return (read_seqcount_begin(&seqlock->seql_count));
+}
+
+#define	read_seqretry(seqlock, gen)	\
+	read_seqcount_retry(&(seqlock)->seql_count, gen)
+
+#endif	/* _LINUX_SEQLOCK_H__ */