linux-kernel - Re: [PATCH v2 2/3] i2c: imx: Check for I2SR

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Message-ID: <3765943.G7FBkpUTMe@n95hx1g2>
Date:   Mon, 5 Oct 2020 11:25:13 +0200
From:   Christian Eggers <ceggers@...i.de>
To:     Krzysztof Kozlowski <krzk@...nel.org>
CC:     Oleksij Rempel <linux@...pel-privat.de>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        NXP Linux Team <linux-imx@....com>,
        <linux-i2c@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <stable@...r.kernel.org>
Subject: Re: [PATCH v2 2/3] i2c: imx: Check for I2SR_IAL after every byte

On Monday, 5 October 2020, 10:07:25 CEST, Krzysztof Kozlowski wrote:
> The I2C on Vybrid VF500 still works fine. I did not test this actual
> condition (arbitration) but only a regular I2C driver (BQ27xxx fuel
> gauge). Obviously this only proves that regular operation is not
> broken...
thank you very much for testing on Vybrid.

> Alternatively if you have a specific testing procedure (reproduction of
> a problem), please share.

The IAL errors happen due to noise on our I2C bus. We have our power supply 
connected via I2C. The hardware designers wanted to make sure that no
high currents flow through the ground pins of the I2C interface. So they added 
a series resistor (30 Ohm) in the GND line between the power supply and the 
i.MX board.

If you have an I2C device on an external PCB, adding some small series 
resistance in the GND line may cause IAL errors. On the other hand, if 
everything else works fine, also handling if IAL should work on Vybrid.

> Best regards,
> Krzysztof
Best regards
Christian