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

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Message-ID: <cnwphrjjrakaafm7zp725mickh63xw5qm6mlh6q43745ljgxfe@33y2z234oauu>
Date: Thu, 26 Dec 2024 02:21:58 +0100
From: Andi Shyti <andi.shyti@...nel.org>
To: "Lad, Prabhakar" <prabhakar.csengg@...il.com>
Cc: Wolfram Sang <wsa+renesas@...g-engineering.com>, 
	Chris Brandt <chris.brandt@...esas.com>, 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,

On Mon, Dec 23, 2024 at 06:35:28AM +0000, Lad, Prabhakar wrote:
> On Sun, Dec 22, 2024 at 12:44 PM Wolfram Sang
> > > ● 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.

Wolfram has commented on a very valid point, on a standard i2c
specification.

I'd like to merge this once all the hardware questions are
answered.

Please, do follow up on this.

Thanks,
Andi