linux-kernel - Re: [PATCH V3 1/2] i2c-designware: Add i2c bus locking support

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Message-ID: <20141204184947.GB1530@pathfinder>
Date:	Thu, 4 Dec 2014 10:49:47 -0800
From:	"David E. Box" <david.e.box@...ux.intel.com>
To:	Mika Westerberg <mika.westerberg@...ux.intel.com>
Cc:	wsa@...-dreams.de, jdelvare@...e.de, arnd@...db.de,
	maxime.ripard@...e-electrons.com, dianders@...omium.org,
	u.kleine-koenig@...gutronix.de,
	laurent.pinchart+renesas@...asonboard.com,
	boris.brezillon@...e-electrons.com, andrew@...n.ch,
	sjg@...omium.org, markus.mayer@...aro.org,
	jacob.jun.pan@...ux.intel.com, max.schwarz@...ine.de,
	skuribay@...ox.com, Romain.Baeriswyl@...lis.com,
	wenkai.du@...el.com, chiau.ee.chew@...el.com, alan@...ux.intel.com,
	linux-kernel@...r.kernel.org, linux-i2c@...r.kernel.org
Subject: Re: [PATCH V3 1/2] i2c-designware: Add i2c bus locking support

On Wed, Dec 03, 2014 at 06:01:25PM +0200, Mika Westerberg wrote:
> On Mon, Dec 01, 2014 at 04:09:32PM -0800, David E. Box wrote:
> > Adds support for acquiring and releasing a hardware bus lock in the i2c
> > designware core transfer function. This is needed for i2c bus controllers
> > that are shared with but not controlled by the kernel.
> > 
> > Signed-off-by: David E. Box <david.e.box@...ux.intel.com>
> > ---
> >  drivers/i2c/busses/i2c-designware-core.c    | 11 +++++++++++
> >  drivers/i2c/busses/i2c-designware-core.h    |  6 ++++++
> >  drivers/i2c/busses/i2c-designware-platdrv.c | 18 +++++++++++++-----
> >  3 files changed, 30 insertions(+), 5 deletions(-)
> > 
> > diff --git a/drivers/i2c/busses/i2c-designware-core.c b/drivers/i2c/busses/i2c-designware-core.c
> > index 3c20e4b..377deeb 100644
> > --- a/drivers/i2c/busses/i2c-designware-core.c
> > +++ b/drivers/i2c/busses/i2c-designware-core.c
> > @@ -631,6 +631,14 @@ i2c_dw_xfer(struct i2c_adapter *adap, struct i2c_msg msgs[], int num)
> >  	dev->abort_source = 0;
> >  	dev->rx_outstanding = 0;
> >  
> > +	if (dev->acquire_lock) {
> > +		ret = dev->acquire_lock(dev);
> > +		if (ret) {
> > +			dev_err(dev->dev, "couldn't acquire bus ownership\n");
> > +			goto done;
> 
> I wonder what happens now since you failed to acquire the lock...
> 
> > +		}
> > +	}
> > +
> >  	ret = i2c_dw_wait_bus_not_busy(dev);
> >  	if (ret < 0)
> >  		goto done;
> > @@ -676,6 +684,9 @@ i2c_dw_xfer(struct i2c_adapter *adap, struct i2c_msg msgs[], int num)
> >  	ret = -EIO;
> >  
> >  done:
> > +	if (dev->release_lock)
> > +		dev->release_lock(dev);
> 
> ... but here you unconditionally release it?
> 

Releasing the lock unconditionally isn't a problem, but it is an unnecessary
path should we fail to acquire the lock. I'll add another label to skip it.

Dave


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