linux-kernel - Re: [PATCH v2 9/9] i2c: riic: Implement bus recovery

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Message-ID: <CA+V-a8s+tY6dnVHFhjyOZ43L+roLfqPr-_28FS1KyADwyTH2+w@mail.gmail.com>
Date: Mon, 23 Dec 2024 06:35:28 +0000
From: "Lad, Prabhakar" <prabhakar.csengg@...il.com>
To: Wolfram Sang <wsa+renesas@...g-engineering.com>, 
	"Lad, Prabhakar" <prabhakar.csengg@...il.com>, Chris Brandt <chris.brandt@...esas.com>, 
	Andi Shyti <andi.shyti@...nel.org>, Philipp Zabel <p.zabel@...gutronix.de>, 
	Wolfram Sang <wsa@...nel.org>, Geert Uytterhoeven <geert+renesas@...der.be>, 
	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 v2 9/9] i2c: riic: Implement bus recovery

Hi Wolfram,

On Sun, Dec 22, 2024 at 12:44 PM Wolfram Sang
<wsa+renesas@...g-engineering.com> wrote:
>
>
> > On the RZ/G2L and RZ/G3S there is a restriction for forcing the SDA/SCL states:
> >
> > ● Write:
> > 0: Changes the RIICnSCL/RIICnSDA pin output to a low level.
> > 1: Changes the RIICnSCL/RIICnSDA pin in a high-impedance state.
> > (High level output is achieved through an external pull-up resistor.)
> >
> > So using the generic algorithm may be platform dependent as it would
> > only work on platforms which have external pull-up resistor on SDA/SCL
> > pins. So to overcome this and make recovery possible on the platforms
> > I choose the RIIC feature to output clock cycles as required.
>
> I would be super-surprised if this is really a restriction and not a
> very precise documentation. In other words, I am quite sure that there
> is no difference between the bit forcing SCL high (via high-impedance)
> and the internal RIIC handling when it needs SCL high. Most I2C busses
> are open-drain anyhow.
>
I had asked this previously to the HW engineers about the requirement
(as this restriction is not mentioned in the RZ/V2H(P) SoC, Ive seen
it for RZ/A series RZ/G2L family and RZ/G3S only) before the start of
the I2C recovery work but haven't got a response yet. Ive pinged them
again and I'll wait for their feedback.

Cheers,
Prabhakar