Some platforms have MMIO regions that are shared across orthogonal
subsystems. This commit implements a possible solution for the
thread-safe access of such regions through a spinlock-protected API.
Concurrent access is protected with a single spinlock for the
entire MMIO address space. While this protects shared-registers,
it also serializes access to unrelated/unshared registers.
Signed-off-by: Ezequiel Garcia <ezequiel.gar...@free-electrons.com>
---
include/linux/io.h | 5 +++++
lib/Makefile | 2 +-
lib/atomicio.c | 27 +++++++++++++++++++++++++++
3 files changed, 33 insertions(+), 1 deletion(-)
create mode 100644 lib/atomicio.c
diff --git a/include/linux/io.h b/include/linux/io.h
index f4f42fa..c331dcb 100644
--- a/include/linux/io.h
+++ b/include/linux/io.h
@@ -101,4 +101,9 @@ static inline void arch_phys_wc_del(int handle)
#define arch_phys_wc_add arch_phys_wc_add
#endif
+#ifndef __HAVE_ARCH_ATOMIC_IO_MODIFY
+/* Atomic MMIO-wide IO modify */
+extern void atomic_io_modify(void __iomem *reg, u32 mask, u32 set);
+#endif
+
#endif /* _LINUX_IO_H */
diff --git a/lib/Makefile b/lib/Makefile
index 7baccfd..695d6e2 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -13,7 +13,7 @@ lib-y := ctype.o string.o vsprintf.o cmdline.o \
sha1.o md5.o irq_regs.o reciprocal_div.o argv_split.o \
proportions.o flex_proportions.o prio_heap.o ratelimit.o show_mem.o \
is_single_threaded.o plist.o decompress.o kobject_uevent.o \
- earlycpio.o percpu-refcount.o
+ earlycpio.o percpu-refcount.o atomicio.o
obj-$(CONFIG_ARCH_HAS_DEBUG_STRICT_USER_COPY_CHECKS) += usercopy.o
lib-$(CONFIG_MMU) += ioremap.o
diff --git a/lib/atomicio.c b/lib/atomicio.c
new file mode 100644
index 0000000..1750f9d
--- /dev/null
+++ b/lib/atomicio.c
@@ -0,0 +1,27 @@
+#include <linux/io.h>
+#include <linux/spinlock.h>
+
+#ifndef __HAVE_ARCH_ATOMIC_IO_MODIFY
+/*
+ * Generic atomic MMIO modify.
+ *
+ * Allows thread-safe access to registers shared by unrelated subsystems.
+ * The access is protected by a single MMIO-wide lock.
+ *
+ * Optimized variants can be implemented on a per-architecture basis.
+ */
+static DEFINE_RAW_SPINLOCK(__io_lock);
+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(reg) & ~mask;
+ value |= (set & mask);
+ writel(value, reg);
+ raw_spin_unlock_irqrestore(&__io_lock, flags);
+
+}
+EXPORT_SYMBOL(atomic_io_modify);
+#endif
--
1.8.1.5
--
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