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

Mika Westerberg
2014-06-02T17:34:35Z

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@linux.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
> >