v4.19.13 snapshot.
diff --git a/arch/arm/kernel/io.c b/arch/arm/kernel/io.c
new file mode 100644
index 0000000..60b6212
--- /dev/null
+++ b/arch/arm/kernel/io.c
@@ -0,0 +1,85 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/export.h>
+#include <linux/types.h>
+#include <linux/io.h>
+#include <linux/spinlock.h>
+
+static DEFINE_RAW_SPINLOCK(__io_lock);
+
+/*
+ * Generic atomic MMIO modify.
+ *
+ * Allows thread-safe access to registers shared by unrelated subsystems.
+ * The access is protected by a single MMIO-wide lock.
+ */
+void atomic_io_modify_relaxed(void __iomem *reg, u32 mask, u32 set)
+{
+ unsigned long flags;
+ u32 value;
+
+ raw_spin_lock_irqsave(&__io_lock, flags);
+ value = readl_relaxed(reg) & ~mask;
+ value |= (set & mask);
+ writel_relaxed(value, reg);
+ raw_spin_unlock_irqrestore(&__io_lock, flags);
+}
+EXPORT_SYMBOL(atomic_io_modify_relaxed);
+
+void atomic_io_modify(void __iomem *reg, u32 mask, u32 set)
+{
+ unsigned long flags;
+ u32 value;
+
+ raw_spin_lock_irqsave(&__io_lock, flags);
+ value = readl_relaxed(reg) & ~mask;
+ value |= (set & mask);
+ writel(value, reg);
+ raw_spin_unlock_irqrestore(&__io_lock, flags);
+}
+EXPORT_SYMBOL(atomic_io_modify);
+
+/*
+ * Copy data from IO memory space to "real" memory space.
+ * This needs to be optimized.
+ */
+void _memcpy_fromio(void *to, const volatile void __iomem *from, size_t count)
+{
+ unsigned char *t = to;
+ while (count) {
+ count--;
+ *t = readb(from);
+ t++;
+ from++;
+ }
+}
+EXPORT_SYMBOL(_memcpy_fromio);
+
+/*
+ * Copy data from "real" memory space to IO memory space.
+ * This needs to be optimized.
+ */
+void _memcpy_toio(volatile void __iomem *to, const void *from, size_t count)
+{
+ const unsigned char *f = from;
+ while (count) {
+ count--;
+ writeb(*f, to);
+ f++;
+ to++;
+ }
+}
+EXPORT_SYMBOL(_memcpy_toio);
+
+/*
+ * "memset" on IO memory space.
+ * This needs to be optimized.
+ */
+void _memset_io(volatile void __iomem *dst, int c, size_t count)
+{
+ while (count) {
+ count--;
+ writeb(c, dst);
+ dst++;
+ }
+}
+EXPORT_SYMBOL(_memset_io);