linux-kernel - Re: [PATCH v4 2/4] ARM: Add atomic_io

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Message-ID: <20130828085340.GB58219@MacBook-Pro.local>
Date:	Wed, 28 Aug 2013 09:53:40 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	Ezequiel Garcia <ezequiel.garcia@...e-electrons.com>
Cc:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	Gregory Clement <gregory.clement@...e-electrons.com>,
	Lior Amsalem <alior@...vell.com>,
	Baruch Siach <baruch@...s.co.il>,
	Will Deacon <Will.Deacon@....com>,
	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
	Russell King <linux@....linux.org.uk>
Subject: Re: [PATCH v4 2/4] ARM: Add atomic_io_modify optimized routines

On Sat, Aug 24, 2013 at 04:35:30PM +0100, Ezequiel Garcia wrote:
> Implement arch-specific atomic_io_modify and atomic_io_modify_relaxed,
> which are based on writel/readl_relaxed and writel_relaxed/readl_relaxed,
> respectively.
> In both cases, by relaxing the readl, perfomance can be improved.
> 
> Signed-off-by: Ezequiel Garcia <ezequiel.garcia@...e-electrons.com>
> ---
>  arch/arm/include/asm/io.h |  4 ++++
>  arch/arm/kernel/io.c      | 29 +++++++++++++++++++++++++++++
>  2 files changed, 33 insertions(+)
> 
> diff --git a/arch/arm/include/asm/io.h b/arch/arm/include/asm/io.h
> index d070741..53637b6 100644
> --- a/arch/arm/include/asm/io.h
> +++ b/arch/arm/include/asm/io.h
> @@ -397,5 +397,9 @@ extern int devmem_is_allowed(unsigned long pfn);
>  extern void register_isa_ports(unsigned int mmio, unsigned int io,
>  			       unsigned int io_shift);
>  
> +#define __HAVE_ARCH_ATOMIC_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);
> +
>  #endif	/* __KERNEL__ */
>  #endif	/* __ASM_ARM_IO_H */
> diff --git a/arch/arm/kernel/io.c b/arch/arm/kernel/io.c
> index dcd5b4d..a8c9c9b 100644
> --- a/arch/arm/kernel/io.c
> +++ b/arch/arm/kernel/io.c
> @@ -1,6 +1,35 @@
>  #include <linux/export.h>
>  #include <linux/types.h>
>  #include <linux/io.h>
> +#include <linux/spinlock.h>
> +
> +static DEFINE_RAW_SPINLOCK(__io_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);

Is this any different from the generic one introduced in patch 1/4? I
would rather just use the generic definition. Similarly, a generic
atomic_io_modify_relaxed() but guarded with something like
__HAVE_ARCH_RELAXED_IO.

-- 
Catalin
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