v4.19.13 snapshot.
diff --git a/drivers/clocksource/mmio.c b/drivers/clocksource/mmio.c
new file mode 100644
index 0000000..4c4df98
--- /dev/null
+++ b/drivers/clocksource/mmio.c
@@ -0,0 +1,73 @@
+/*
+ * Generic MMIO clocksource support
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+#include <linux/clocksource.h>
+#include <linux/errno.h>
+#include <linux/init.h>
+#include <linux/slab.h>
+
+struct clocksource_mmio {
+ void __iomem *reg;
+ struct clocksource clksrc;
+};
+
+static inline struct clocksource_mmio *to_mmio_clksrc(struct clocksource *c)
+{
+ return container_of(c, struct clocksource_mmio, clksrc);
+}
+
+u64 clocksource_mmio_readl_up(struct clocksource *c)
+{
+ return (u64)readl_relaxed(to_mmio_clksrc(c)->reg);
+}
+
+u64 clocksource_mmio_readl_down(struct clocksource *c)
+{
+ return ~(u64)readl_relaxed(to_mmio_clksrc(c)->reg) & c->mask;
+}
+
+u64 clocksource_mmio_readw_up(struct clocksource *c)
+{
+ return (u64)readw_relaxed(to_mmio_clksrc(c)->reg);
+}
+
+u64 clocksource_mmio_readw_down(struct clocksource *c)
+{
+ return ~(u64)readw_relaxed(to_mmio_clksrc(c)->reg) & c->mask;
+}
+
+/**
+ * clocksource_mmio_init - Initialize a simple mmio based clocksource
+ * @base: Virtual address of the clock readout register
+ * @name: Name of the clocksource
+ * @hz: Frequency of the clocksource in Hz
+ * @rating: Rating of the clocksource
+ * @bits: Number of valid bits
+ * @read: One of clocksource_mmio_read*() above
+ */
+int __init clocksource_mmio_init(void __iomem *base, const char *name,
+ unsigned long hz, int rating, unsigned bits,
+ u64 (*read)(struct clocksource *))
+{
+ struct clocksource_mmio *cs;
+
+ if (bits > 64 || bits < 16)
+ return -EINVAL;
+
+ cs = kzalloc(sizeof(struct clocksource_mmio), GFP_KERNEL);
+ if (!cs)
+ return -ENOMEM;
+
+ cs->reg = base;
+ cs->clksrc.name = name;
+ cs->clksrc.rating = rating;
+ cs->clksrc.read = read;
+ cs->clksrc.mask = CLOCKSOURCE_MASK(bits);
+ cs->clksrc.flags = CLOCK_SOURCE_IS_CONTINUOUS;
+
+ return clocksource_register_hz(&cs->clksrc, hz);
+}