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Commit c5ca95b5 authored by Ezequiel Garcia's avatar Ezequiel Garcia Committed by Russell King
Browse files

ARM: 7930/1: Introduce atomic MMIO modify 



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: default avatarSebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Acked-by: default avatarJason Cooper <jason@lakedaemon.net>
Acked-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
Signed-off-by: default avatarEzequiel Garcia <ezequiel.garcia@free-electrons.com>
Signed-off-by: default avatarRussell King <rmk+kernel@arm.linux.org.uk>
parent 668bc386

arch/arm/include/asm/io.h

+6 −0
Original line number Diff line number Diff line
@@ -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.

arch/arm/kernel/io.c

+35 −0
Original line number Diff line number Diff line 
#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.