linux-kernel - Re: Sony IMX290/462 image sensors I2C xfer peculiarity

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Message-ID: <ZSjvA3QpY1T9McjN@ninjato>
Date:   Fri, 13 Oct 2023 09:17:23 +0200
From:   Wolfram Sang <wsa@...nel.org>
To:     Stefan Lengfeld <stefan@...gfeld.xyz>
Cc:     Krzysztof Hałasa <khalasa@...p.pl>,
        linux-media <linux-media@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Dave Stevenson <dave.stevenson@...pberrypi.com>,
        Oleksij Rempel <linux@...pel-privat.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>, linux-i2c@...r.kernel.org
Subject: Re: Sony IMX290/462 image sensors I2C xfer peculiarity


> Do you know the I2C repeated start feature [1]? This allows to batch together
> multiple I2C read/writes in a single transfer. And in the best case, this
> transfer is executed in one go without a delay in between. At least in the
> kernel it's guaranteed that no other driver can go in between with another
> transfer.

If the HW does rep_start properly, it is even guaranteed on the bus
because the bus is never seen as free by other participants. Check
"START and STOP" conditions in the I2C specs.


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