linux-kernel - Re: [PATCH 1/4] i2c: designware: No need to disable already disabled controller

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Date:	Mon, 2 Jun 2014 20:34:08 +0300
From:	Mika Westerberg <mika.westerberg@...ux.intel.com>
To:	Wolfram Sang <wsa@...-dreams.de>
Cc:	Yao Jin <yao.jin@...el.com>, Aubrey Li <aubrey.li@...el.com>,
	linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] i2c: designware: No need to disable already disabled
 controller

On Mon, Jun 02, 2014 at 06:12:34PM +0200, Wolfram Sang wrote:
> On Thu, May 15, 2014 at 05:37:21PM +0300, Mika Westerberg wrote:
> > If the controller is already in desired state (enabled/disabled) there is
> > no point in setting its state again.
> > 
> > Signed-off-by: Mika Westerberg <mika.westerberg@...ux.intel.com>
> > ---
> 
> Does it have a side-effect when setting then enable bit again? Otherwise
> it will exit the loop immediately on the first try. Not too bad IMO
> given the additional code saved.

AFAICT there shouldn't be any side effect. So the $subject patch just
saves one register write in the best case. You are right, maybe it's not
worth adding 3 extra lines of code just for that :)

> 
> >  drivers/i2c/busses/i2c-designware-core.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> > 
> > diff --git a/drivers/i2c/busses/i2c-designware-core.c b/drivers/i2c/busses/i2c-designware-core.c
> > index b58ecf19e767..b0792675b970 100644
> > --- a/drivers/i2c/busses/i2c-designware-core.c
> > +++ b/drivers/i2c/busses/i2c-designware-core.c
> > @@ -258,6 +258,10 @@ static void __i2c_dw_enable(struct dw_i2c_dev *dev, bool enable)
> >  {
> >  	int timeout = 100;
> >  
> > +	/* In case the controller is already in desired state */
> > +	if ((dw_readl(dev, DW_IC_ENABLE_STATUS) & 1) == enable)
> > +		return;
> > +
> >  	do {
> >  		dw_writel(dev, enable, DW_IC_ENABLE);
> >  		if ((dw_readl(dev, DW_IC_ENABLE_STATUS) & 1) == enable)
> > -- 
> > 2.0.0.rc2
> > 


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