linux-kernel - Re: [PATCH v1 1/2] arm64: dts: imx8mm-verdin: add single-master property to all i2c nodes

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Message-ID: <ZyY33Ai6xndqTHzi@eichest-laptop>
Date: Sat, 2 Nov 2024 15:31:56 +0100
From: Stefan Eichenberger <eichest@...il.com>
To: Shawn Guo <shawnguo2@...h.net>
Cc: robh@...nel.org, krzk+dt@...nel.org, conor+dt@...nel.org,
	shawnguo@...nel.org, s.hauer@...gutronix.de, kernel@...gutronix.de,
	festevam@...il.com, francesco.dolcini@...adex.com,
	devicetree@...r.kernel.org, imx@...ts.linux.dev,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Stefan Eichenberger <stefan.eichenberger@...adex.com>
Subject: Re: [PATCH v1 1/2] arm64: dts: imx8mm-verdin: add single-master
 property to all i2c nodes

Hi Shawn,

On Sat, Nov 02, 2024 at 12:52:08PM +0800, Shawn Guo wrote:
> On Fri, Oct 25, 2024 at 11:58:02AM +0200, Stefan Eichenberger wrote:
> > From: Stefan Eichenberger <stefan.eichenberger@...adex.com>
> > 
> > By default we expect all i2c nodes to be single-master, we do not have
> > any module or carrier board that uses multi-master mode on any i2c
> > controller. With this property set, we benefit from optimisations made
> > exclusively for single-masters.
> > 
> > Signed-off-by: Stefan Eichenberger <stefan.eichenberger@...adex.com>
> > ---
> >  arch/arm64/boot/dts/freescale/imx8mm-verdin.dtsi | 4 ++++
> >  1 file changed, 4 insertions(+)
> > 
> > diff --git a/arch/arm64/boot/dts/freescale/imx8mm-verdin.dtsi b/arch/arm64/boot/dts/freescale/imx8mm-verdin.dtsi
> > index 5fa3959141911..95d5d2333ca1e 100644
> > --- a/arch/arm64/boot/dts/freescale/imx8mm-verdin.dtsi
> > +++ b/arch/arm64/boot/dts/freescale/imx8mm-verdin.dtsi
> > @@ -367,6 +367,7 @@ &i2c1 {
> >  	pinctrl-1 = <&pinctrl_i2c1_gpio>;
> >  	scl-gpios = <&gpio5 14 (GPIO_ACTIVE_HIGH | GPIO_OPEN_DRAIN)>;
> >  	sda-gpios = <&gpio5 15 (GPIO_ACTIVE_HIGH | GPIO_OPEN_DRAIN)>;
> > +	single-master;
> 
> Hmm, I do not see this property is documented in i2c-imx bindings.

According to the discussion we had in this thread
https://lore.kernel.org/linux-i2c/2bbddaxyjkxfmlgmq3yqcbzo7dsb2pq5bvdatk2y4ig4iintkt@35btqkdv7sy3/
it is not necessary to have the property documentation in the i2c-imx
binding because it is already documented in the dt-schema:
https://github.com/devicetree-org/dt-schema/blob/main/dtschema/schemas/i2c/i2c-controller.yaml
In the initial discussion, it was addressed for multi-master setups, but
it also applies for single-master. See also this discussion:
https://lore.kernel.org/all/bcdd6cae28edd9dd05a71118f9979e7460688775.camel@pengutronix.de/

Let me know if I have missed anything or misunderstood.

Regards,
Stefan