linux-kernel - Re: [PATCH v5 2/3] I2C: mediatek: Add driver for MediaTek I2C controller

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Message-ID: <1427802658.32196.8.camel@mtksdaap41>
Date:	Tue, 31 Mar 2015 19:50:58 +0800
From:	Eddie Huang <eddie.huang@...iatek.com>
To:	Sascha Hauer <s.hauer@...gutronix.de>
CC:	Mark Rutland <mark.rutland@....com>,
	Wolfram Sang <wsa@...-dreams.de>,
	Doug Anderson <dianders@...omium.org>,
	"linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
	David Box <david.e.box@...ux.intel.com>,
	Lee Jones <lee.jones@...aro.org>,
	Jean Delvare <jdelvare@...e.de>,
	Xudong Chen (陈旭东) 
	<Xudong.Chen@...iatek.com>,
	Boris BREZILLON <boris.brezillon@...e-electrons.com>,
	Pawel Moll <pawel.moll@....com>,
	Liguo Zhang (张立国) 
	<Liguo.Zhang@...iatek.com>, Wei Yan <sledge.yanwei@...wei.com>,
	Bjorn Andersson <bjorn.andersson@...ymobile.com>,
	Uwe Kleine-Konig <u.kleine-koenig@...gutronix.de>,
	Neelesh Gupta <neelegup@...ux.vnet.ibm.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Arnd Bergmann <arnd@...db.de>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Beniamino Galvani <b.galvani@...il.com>,
	Rob Herring <robh+dt@...nel.org>,
	"linux-mediatek@...ts.infradead.org" 
	<linux-mediatek@...ts.infradead.org>,
	Matthias Brugger <matthias.bgg@...il.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	srv_heupstream <srv_heupstream@...iatek.com>,
	Anders Berg <anders.berg@...gotech.com>,
	Jim Cromie <jim.cromie@...il.com>,
	Simon Glass <sjg@...omium.org>,
	Max Schwarz <max.schwarz@...ine.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Sascha Hauer <kernel@...gutronix.de>,
	Kumar Gala <galak@...eaurora.org>
Subject: Re: [PATCH v5 2/3] I2C: mediatek: Add driver for MediaTek I2C
 controller

Hi Sascha,

On Tue, 2015-03-31 at 15:08 +0800, Eddie Huang wrote:
> Hi Sascha,
> 
> On Mon, 2015-03-30 at 19:23 +0200, Sascha Hauer wrote:
> > On Mon, Mar 30, 2015 at 04:14:12PM +0800, Eddie Huang wrote:
> > > Hi Sascha,
> > >
> > > >
> > > > [...]
> > > >
> > > > > +       if (i2c->speed_hz > 400000)
> > > > > +               control_reg |= I2C_CONTROL_RS;
> > > > > +       if (i2c->op == I2C_MASTER_WRRD)
> > > > > +               control_reg |= I2C_CONTROL_DIR_CHANGE | I2C_CONTROL_RS;
> > > > > +       mtk_i2c_writew(control_reg, i2c, OFFSET_CONTROL);
> > > > > +
> > > > > +       /* set start condition */
> > > > > +       if (i2c->speed_hz <= 100000)
> > > > > +               mtk_i2c_writew(I2C_ST_START_CON, i2c, OFFSET_EXT_CONF);
> > > > > +       else
> > > > > +               mtk_i2c_writew(I2C_FS_START_CON, i2c, OFFSET_EXT_CONF);
> > > > > +
> > > > > +       if (~control_reg & I2C_CONTROL_RS)
> > > > > +               mtk_i2c_writew(I2C_DELAY_LEN, i2c, OFFSET_DELAY_LEN);
> > > >
> > > > speed <= 400000 here to make this more obvious?
> > > There are two cases, not only speed<=400000, but I2C_MASTER_WRRD. I tend
> > > to keep it.
> >
> > Still it looks strange. You only ever write this default value to the
> > register. Putting this register write under an if() seems bogus since
> > the same value will be in the register the next time this code is
> > executed. It looks like you should move this register write to some
> > initialization function.
> OK, move to mtk_i2c_init_hw function
> 
Sorry for my negligence. Write-then-read (I2C_MASTER_WRRD) decides
according to each I2C transfer, so I still need to judge whether set
I2C_CONTROL_RS and DELAY_LEN here. Other control setting can move to
init function.

Eddie



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