linux-kernel - Re: [PATCH v9 2/2] i2c: riic: Recover from arbitration loss

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Message-ID: <aBMpjKtQYYB-teNt@shikoro>
Date: Thu, 1 May 2025 09:58:04 +0200
From: Wolfram Sang <wsa+renesas@...g-engineering.com>
To: "Lad, Prabhakar" <prabhakar.csengg@...il.com>
Cc: Chris Brandt <chris.brandt@...esas.com>,
	Andi Shyti <andi.shyti@...nel.org>,
	Geert Uytterhoeven <geert+renesas@...der.be>,
	Andy Shevchenko <andy@...nel.org>,
	linux-renesas-soc@...r.kernel.org, linux-i2c@...r.kernel.org,
	linux-kernel@...r.kernel.org, Biju Das <biju.das.jz@...renesas.com>,
	Fabrizio Castro <fabrizio.castro.jz@...esas.com>,
	Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
Subject: Re: [PATCH v9 2/2] i2c: riic: Recover from arbitration loss


> Do you mean that upon detecting an arbitration loss, we simply clear
> the arbitration bit and retry?

Yes, after the bus is considered free again.

> However, when observing the SDA line after recovery, it goes LOW again
> during the transfer. I've attached a screenshot of this case: we
> recovered from a bus hang, the I2C recovery algorithm brought the bus
> to a STOP state, and then a START condition was issued. But after
> initiating the transfer, we can see the SDA line being held LOW again.

That looks weird. Why are there two SDA transitions around 30us? Why is
SDA changed while SCL is high around 45us? Then, this small SCL spike
around 55us... What device is this?


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