linux-kernel - Re: [PATCH V3 2/2] i2c-designware: Add Intel Baytrail PMIC I2C bus support

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Date:	Thu, 4 Dec 2014 11:11:14 -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 2/2] i2c-designware: Add Intel Baytrail PMIC I2C bus
 support

On Wed, Dec 03, 2014 at 06:10:46PM +0200, Mika Westerberg wrote:
> On Mon, Dec 01, 2014 at 04:09:33PM -0800, David E. Box wrote:
> > This patch implements an I2C bus sharing mechanism between the host and platform
> > hardware on select Intel BayTrail SoC platforms using the X-Powers AXP288 PMIC.
> > 
> > On these platforms access to the PMIC must be shared with platform hardware. The
> > hardware unit assumes full control of the I2C bus and the host must request
> > access through a special semaphore. Hardware control of the bus also makes it
> > necessary to disable runtime pm to avoid interfering with hardware transactions.
> > 
> > Signed-off-by: David E. Box <david.e.box@...ux.intel.com>
> > ---
> >  drivers/i2c/busses/Kconfig                   |  12 +++
> >  drivers/i2c/busses/Makefile                  |   1 +
> >  drivers/i2c/busses/i2c-designware-baytrail.c | 155 +++++++++++++++++++++++++++
> >  drivers/i2c/busses/i2c-designware-core.h     |   6 ++
> >  4 files changed, 174 insertions(+)
> >  create mode 100644 drivers/i2c/busses/i2c-designware-baytrail.c
> > 
> > diff --git a/drivers/i2c/busses/Kconfig b/drivers/i2c/busses/Kconfig
> > index 917c358..d2bfd88 100644
> > --- a/drivers/i2c/busses/Kconfig
> > +++ b/drivers/i2c/busses/Kconfig
> > @@ -464,6 +464,18 @@ config I2C_DESIGNWARE_PCI
> >  	  This driver can also be built as a module.  If so, the module
> >  	  will be called i2c-designware-pci.
> >  
> > +config I2C_DESIGNWARE_BAYTRAIL
> > +	bool "Intel Baytrail I2C semaphore support"
> > +	depends on I2C_DESIGNWARE_PLATFORM=y
> 
> Hmm, is there something preventing to compile this as module?
> 

There were load order issues. This driver is really a support module for the
platform driver. I think Wolfram suggested this earlier but I didn't realize it
until now. The proper solution is to link it conditionally with
i2c-designware-platform.

Dave
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