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ARM: 7930/1: Introduce atomic MMIO modify

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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.

Tested-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Acked-by: Jason Cooper <jason@lakedaemon.net>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
This commit is contained in:
Ezequiel Garcia 2013-12-18 23:08:52 +01:00 • committed by Russell King
parent 668bc38669
commit c5ca95b507
2 changed files with 41 additions and 0 deletions
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6
arch/arm/include/asm/io.h
View file

@ -37,6 +37,12 @@
#define isa_page_to_bus page_to_phys
#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.

35
arch/arm/kernel/io.c
View file

@ -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.