linux-kernel - Re: [PATCH] i2c: designware: use {readl|writel}

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Date:	Fri, 19 Dec 2014 10:43:15 +0800
From:	Jisheng Zhang <jszhang@...vell.com>
To:	"wsa@...-dreams.de" <wsa@...-dreams.de>,
	"linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] i2c: designware: use {readl|writel}_relaxed instead of
 readl/writel

Dear all,

Is there any issue I need to resolve so that the patch can be merged?

Thanks in advance,
Jisheng

On Wed, 10 Dec 2014 22:26:41 -0800
Jisheng Zhang <jszhang@...vell.com> wrote:

> readl/writel is too expensive especially on Cortex A9 w/ outer L2 cache.
> This introduces i2c read/write errors on Marvell BG2/BG2Q SoCs when there
> are heavy L2 cache maintenance operations at the same time.
> 
> The driver does not perform DMA, so it's safe to use the relaxed version.
> From another side, the relaxed io accessor macros are available on all
> architectures now, so we can use the relaxed versions instead.
> 
> Signed-off-by: Jisheng Zhang <jszhang@...vell.com>
> ---
>  drivers/i2c/busses/i2c-designware-core.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-designware-core.c
> b/drivers/i2c/busses/i2c-designware-core.c index 23628b7..e279948 100644
> --- a/drivers/i2c/busses/i2c-designware-core.c
> +++ b/drivers/i2c/busses/i2c-designware-core.c
> @@ -170,10 +170,10 @@ u32 dw_readl(struct dw_i2c_dev *dev, int offset)
>  	u32 value;
>  
>  	if (dev->accessor_flags & ACCESS_16BIT)
> -		value = readw(dev->base + offset) |
> -			(readw(dev->base + offset + 2) << 16);
> +		value = readw_relaxed(dev->base + offset) |
> +			(readw_relaxed(dev->base + offset + 2) << 16);
>  	else
> -		value = readl(dev->base + offset);
> +		value = readl_relaxed(dev->base + offset);
>  
>  	if (dev->accessor_flags & ACCESS_SWAP)
>  		return swab32(value);
> @@ -187,10 +187,10 @@ void dw_writel(struct dw_i2c_dev *dev, u32 b, int
> offset) b = swab32(b);
>  
>  	if (dev->accessor_flags & ACCESS_16BIT) {
> -		writew((u16)b, dev->base + offset);
> -		writew((u16)(b >> 16), dev->base + offset + 2);
> +		writew_relaxed((u16)b, dev->base + offset);
> +		writew_relaxed((u16)(b >> 16), dev->base + offset + 2);
>  	} else {
> -		writel(b, dev->base + offset);
> +		writel_relaxed(b, dev->base + offset);
>  	}
>  }
>  

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