linux-kernel - Re: [PATCH v8 2/5] i2c: Add STM32F4 I2C driver

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Date:   Fri, 13 Jan 2017 08:26:50 +0100
From:   Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
To:     M'boumba Cedric Madianga <cedric.madianga@...il.com>
Cc:     Wolfram Sang <wsa@...-dreams.de>, Rob Herring <robh+dt@...nel.org>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Patrice Chotard <patrice.chotard@...com>,
        Russell King <linux@...linux.org.uk>,
        linux-i2c@...r.kernel.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 2/5] i2c: Add STM32F4 I2C driver

Hello,

On Thu, Jan 12, 2017 at 10:28:20PM +0100, M'boumba Cedric Madianga wrote:
> Please see below a quote from datasheet that clearly described how to handle
> For 2-byte reception:
> ● Wait until ADDR = 1 (SCL stretched low until the ADDR flag is cleared)
> ● Set ACK low, set POS high
> ● Clear ADDR flag
> ● Wait until BTF = 1 (Data 1 in DR, Data2 in shift register, SCL
> stretched low until a data1 is read)
> ● Set STOP high
> ● Read data 1 and 2

The problem is that you only know that you have a 2 byte transfer after
you read the first byte (and it's a 1). (But note that this is
irrelevant for the patch as the driver doesn't claim to support this
kind of transfer.)

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |