linux-kernel - Re: [PATCH v2 1/2] i2c: mediatek: add i2c first write then read optimization

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Message-ID: <1447116653.24760.1.camel@mtksdaap41>
Date:	Tue, 10 Nov 2015 08:50:53 +0800
From:	Yingjoe Chen <yingjoe.chen@...iatek.com>
To:	Andy Shevchenko <andy.shevchenko@...il.com>
CC:	Liguo Zhang <liguo.zhang@...iatek.com>,
	Xudong Chen <xudong.chen@...iatek.com>,
	<srv_heupstream@...iatek.com>, Wolfram Sang <wsa@...-dreams.de>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	<linux-mediatek@...ts.infradead.org>, <linux-i2c@...r.kernel.org>,
	Matthias Brugger <matthias.bgg@...il.com>,
	"Eddie Huang" <eddie.huang@...iatek.com>,
	linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2 1/2] i2c: mediatek: add i2c first write then read
 optimization

On Mon, 2015-11-09 at 16:25 +0200, Andy Shevchenko wrote:
> On Mon, Nov 9, 2015 at 7:43 AM, Liguo Zhang <liguo.zhang@...iatek.com> wrote:
> > For platform with auto restart support, between every transfer,
> > i2c controller will trigger an interrupt and SW need to handle
> > it to start new transfer. When doing write-then-read transfer,
> > instead of restart mechanism, using WRRD mode to have controller
> > send both transfer in one request to reduce latency.
> 
> 
> > @@ -518,6 +529,16 @@ static int mtk_i2c_transfer(struct i2c_adapter *adap,
> >         if (ret)
> >                 return ret;
> >
> > +       i2c->auto_restart = i2c->dev_comp->auto_restart;
> > +
> > +       /* checking if we can skip restart and optimize using WRRD mode */
> > +       if (i2c->auto_restart && num == 2) {
> > +               if (!(msgs[0].flags & I2C_M_RD) && (msgs[1].flags & I2C_M_RD) &&
> > +                   msgs[0].addr == msgs[1].addr) {
> 
> Nitpick (optional):
> 
> ((msgs[0].flags & msgs[1].flags) & I2C_M_RD)
> ?

These 2 check for different conditions.
The original one check the first one must NOT set I2C_M_RD, but second
one must set I2C_M_RD.

Joe.C


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