From mboxrd@z Thu Jan  1 00:00:00 1970
From: yingjoe.chen@mediatek.com (Yingjoe Chen)
Date: Tue, 10 Nov 2015 08:50:53 +0800
Subject: [PATCH v2 1/2] i2c: mediatek: add i2c first write then read
 optimization
In-Reply-To: <CAHp75VfutRR0N0bGDYMjFr+nQGFnmuoiA2afvYfuZ2aOy=2qbQ@mail.gmail.com>
References: <1447047839-5223-1-git-send-email-liguo.zhang@mediatek.com>
 <1447047839-5223-2-git-send-email-liguo.zhang@mediatek.com>
 <CAHp75VfutRR0N0bGDYMjFr+nQGFnmuoiA2afvYfuZ2aOy=2qbQ@mail.gmail.com>
Message-ID: <1447116653.24760.1.camel@mtksdaap41>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

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@mediatek.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