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

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Date:	Mon, 9 Nov 2015 16:25:09 +0200
From:	Andy Shevchenko <andy.shevchenko@...il.com>
To:	Liguo Zhang <liguo.zhang@...iatek.com>
Cc:	Wolfram Sang <wsa@...-dreams.de>, srv_heupstream@...iatek.com,
	Matthias Brugger <matthias.bgg@...il.com>,
	Eddie Huang <eddie.huang@...iatek.com>,
	Xudong Chen <xudong.chen@...iatek.com>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	linux-i2c@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>,
	linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH v2 1/2] i2c: mediatek: add i2c first write then read optimization

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)
?

> +                       i2c->auto_restart = 0;
> +               }
> +       }

-- 
With Best Regards,
Andy Shevchenko
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