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

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Date:	Tue, 13 Jan 2015 12:52:05 +0100
From:	Wolfram Sang <wsa@...-dreams.de>
To:	Jisheng Zhang <jszhang@...vell.com>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>
Cc:	"linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
	"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

On Fri, Dec 19, 2014 at 10:43:15AM +0800, Jisheng Zhang wrote:
> Dear all,
> 
> Is there any issue I need to resolve so that the patch can be merged?

Adding Mika to the loop. He uses the driver a lot (and knows other
people who do)...


> 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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