linux-kernel - Re: [PATCH 3/3] I2C: mediatek: Add driver for MediaTek I2C controller

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Message-ID: <20141103081105.GD14482@pengutronix.de>
Date:	Mon, 3 Nov 2014 09:11:05 +0100
From:	Sascha Hauer <s.hauer@...gutronix.de>
To:	Matthias Brugger <matthias.bgg@...il.com>
Cc:	Xudong Chen <xudong.chen@...iatek.com>,
	Mark Rutland <mark.rutland@....com>, arm@...nel.org,
	Wolfram Sang <wsa@...-dreams.de>,
	srv_heupstream <srv_heupstream@...iatek.com>,
	Sascha Hauer <kernel@...gutronix.de>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Russell King <linux@....linux.org.uk>,
	Grant Likely <grant.likely@...aro.org>,
	Jean Delvare <jdelvare@...e.de>, Arnd Bergmann <arnd@...db.de>,
	"devicetree@...r.kernel.org" <devicetree@...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>, linux-i2c@...r.kernel.org,
	Yingjoe Chen <yingjoe.chen@...iatek.com>,
	Eddie Huang <eddie.huang@...iatek.com>,
	Nathan Chung <nathan.chung@...iatek.com>,
	YH Chen <yh.chen@...iatek.com>
Subject: Re: [PATCH 3/3] I2C: mediatek: Add driver for MediaTek I2C controller

On Thu, Oct 30, 2014 at 02:16:04PM +0100, Matthias Brugger wrote:
> 2014-10-29 6:37 GMT+01:00 Xudong Chen <xudong.chen@...iatek.com>:
> > +static int mt_i2c_do_transfer(struct mt_i2c *i2c)
> > +{
> > +       u16 addr_reg;
> > +       u16 control_reg;
> > +       int tmo = i2c->adap.timeout;
> > +
> > +       i2c->trans_stop = false;
> > +       i2c->irq_stat = 0;
> > +
> > +       /* If use i2c pin from PMIC mt6397 side, need set PATH_DIR first */
> > +       if (i2c->have_pmic)
> > +               i2c_writew(I2C_CONTROL_WRAPPER, i2c, OFFSET_PATH_DIR);
> 
> So this is some sort of multiplexer bit, right?
> I think in this case we need to build a multi function device (mfd)
> where the pmic driver will set this bit.

This bit is in the i2c controller register space, so it shouldn't be
controlled by some other driver. I think the configuration of this
register is already in the correct place. What I could think of is that
the PMIC could implement a pinctrl driver and the i2c controller driver
gets the pins from the PMIC. Anyway, the controlling of this bit would
still be in the i2c driver.

Sascha

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