linux-kernel - RE: [EXT] Re: [PATCH 1/3] dt-bindings: i2c: add optional mul-value property to binding

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Message-ID: <AM6PR04MB4357714B5306B136A2765B2C973A0@AM6PR04MB4357.eurprd04.prod.outlook.com>
Date:   Tue, 30 Apr 2019 06:56:03 +0000
From:   Chuanhua Han <chuanhua.han@....com>
To:     Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
CC:     "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
        Leo Li <leoyang.li@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        dl-linux-imx <linux-imx@....com>,
        "festevam@...il.com" <festevam@...il.com>,
        "wsa+renesas@...g-engineering.com" <wsa+renesas@...g-engineering.com>,
        "eha@...f.com" <eha@...f.com>,
        "linux@...pel-privat.de" <linux@...pel-privat.de>,
        Sumit Batra <sumit.batra@....com>,
        "l.stach@...gutronix.de" <l.stach@...gutronix.de>,
        "peda@...ntia.se" <peda@...ntia.se>
Subject: RE: [EXT] Re: [PATCH 1/3] dt-bindings: i2c: add optional mul-value
 property to binding



> -----Original Message-----
> From: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
> Sent: 2019年4月30日 14:38
> To: Chuanhua Han <chuanhua.han@....com>
> Cc: robh+dt@...nel.org; mark.rutland@....com; shawnguo@...nel.org;
> s.hauer@...gutronix.de; Leo Li <leoyang.li@....com>;
> linux-kernel@...r.kernel.org; devicetree@...r.kernel.org;
> linux-arm-kernel@...ts.infradead.org; linux-i2c@...r.kernel.org;
> kernel@...gutronix.de; dl-linux-imx <linux-imx@....com>;
> festevam@...il.com; wsa+renesas@...g-engineering.com; eha@...f.com;
> linux@...pel-privat.de; Sumit Batra <sumit.batra@....com>;
> l.stach@...gutronix.de; peda@...ntia.se
> Subject: [EXT] Re: [PATCH 1/3] dt-bindings: i2c: add optional mul-value
> property to binding
> 
> Caution: EXT Email
> 
> On Tue, Apr 30, 2019 at 12:32:40PM +0800, Chuanhua Han wrote:
> > NXP Layerscape SoC have up to three MUL options available for all
> > divider values, we choice of MUL determines the internal monitor rate
> > of the I2C bus (SCL and SDA signals):
> > A lower MUL value results in a higher sampling rate of the I2C signals.
> > A higher MUL value results in a lower sampling rate of the I2C signals.
> >
> > So in Optional properties we added our custom mul-value property in
> > the binding to select which mul option for the device tree i2c
> > controller node.
> >
> > Signed-off-by: Chuanhua Han <chuanhua.han@....com>
> > ---
> >  Documentation/devicetree/bindings/i2c/i2c-imx.txt | 3 +++
> >  1 file changed, 3 insertions(+)
> >
> > diff --git a/Documentation/devicetree/bindings/i2c/i2c-imx.txt
> > b/Documentation/devicetree/bindings/i2c/i2c-imx.txt
> > index b967544590e8..ba8e7b7b3fa8 100644
> > --- a/Documentation/devicetree/bindings/i2c/i2c-imx.txt
> > +++ b/Documentation/devicetree/bindings/i2c/i2c-imx.txt
> > @@ -18,6 +18,9 @@ Optional properties:
> >  - sda-gpios: specify the gpio related to SDA pin
> >  - pinctrl: add extra pinctrl to configure i2c pins to gpio function for i2c
> >    bus recovery, call it "gpio" state
> > +- mul-value: NXP Layerscape SoC have up to three MUL options
> > +available for all I2C divider values, it describes which MUL we
> > +choose to use for the driver, the values should be 1,2,4.
> 
> Indention is broken.
Yes, I also found this problem, next version I will fix the indent problem
> 
> I wonder why this needs to be configurable on a per-machine/device level.
> What is the trade-off?
According to NXP Layerscape SoC Reference Manual, there are three MUL 
options for i2c controller to configure i2c Bus Frequency Divider Register (IBFD)
to determine the clock Frequency of i2c. 
Some socs (such as ls1046a) have the best performance when MUL=4, 
and the default is MUL=1. 
This option is optional and can be configured by device tree
> 
> Best regards
> Uwe
> 
> --
> Pengutronix e.K.                           | Uwe Kleine-König
> |
> Industrial Linux Solutions                 |
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