[v5,01/20] ARM: Introduce atomic MMIO modify

Commit Message

Ezequiel Garcia Jan. 27, 2014, 3:27 p.m. UTC

Some SoC 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.

We add relaxed and non-relaxed variants, by using writel_relaxed and writel,
respectively. The rationale for this is that some users may not require
register write completion but only thread-safe access to a register.

Cc: Russell King - ARM Linux <[e-mail]>
Tested-by: Sebastian Hesselbarth <[e-mail]>
Signed-off-by: Ezequiel Garcia <[e-mail]>
---
Russell,

Can you confirm this patch is on its way to v3.14?

 arch/arm/include/asm/io.h |  6 ++++++
 arch/arm/kernel/io.c      | 35 +++++++++++++++++++++++++++++++++++
 2 files changed, 41 insertions(+)

Comments

Ezequiel Garcia Jan. 28, 2014, 10:31 a.m. UTC | #1

On Mon, Jan 27, 2014 at 12:27:01PM -0300, Ezequiel Garcia wrote:
> Some SoC 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.
> 
> We add relaxed and non-relaxed variants, by using writel_relaxed and writel,
> respectively. The rationale for this is that some users may not require
> register write completion but only thread-safe access to a register.
> 
> Cc: Russell King - ARM Linux <[e-mail]>
> Tested-by: Sebastian Hesselbarth <[e-mail]>
> Signed-off-by: Ezequiel Garcia <[e-mail]>
> ---
> Russell,
> 
> Can you confirm this patch is on its way to v3.14?
> 

ping?

Patch

diff --git a/arch/arm/include/asm/io.h b/arch/arm/include/asm/io.h
index fbeb39c..8aa4cca 100644
--- a/arch/arm/include/asm/io.h
+++ b/arch/arm/include/asm/io.h
@@ -38,6 +38,12 @@ 
 #define isa_bus_to_virt phys_to_virt
 
 /*
+ * Atomic MMIO-wide IO modify
+ */
+extern void atomic_io_modify(void __iomem *reg, u32 mask, u32 set);
+extern void atomic_io_modify_relaxed(void __iomem *reg, u32 mask, u32 set);
+
+/*
  * Generic IO read/write.  These perform native-endian accesses.  Note
  * that some architectures will want to re-define __raw_{read,write}w.
  */
diff --git a/arch/arm/kernel/io.c b/arch/arm/kernel/io.c
index dcd5b4d..9203cf8 100644
--- a/arch/arm/kernel/io.c
+++ b/arch/arm/kernel/io.c
@@ -1,6 +1,41 @@ 
 #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.