linux-kernel - Re: [PATCH 1/2] i2c: designware: device tree bindings for i2c speed mode

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Message-ID: <20140820093459.GB21174@leverpostej>
Date:	Wed, 20 Aug 2014 10:34:59 +0100
From:	Mark Rutland <mark.rutland@....com>
To:	"atull@...nsource.altera.com" <atull@...nsource.altera.com>
Cc:	"wsa@...-dreams.de" <wsa@...-dreams.de>,
	"baruch@...s.co.il" <baruch@...s.co.il>,
	"mika.westerberg@...ux.intel.com" <mika.westerberg@...ux.intel.com>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	"robh+dt@...nel.org" <robh+dt@...nel.org>,
	"skuribay@...ox.com" <skuribay@...ox.com>,
	"Romain.Baeriswyl@...lis.com" <Romain.Baeriswyl@...lis.com>,
	"rafael.j.wysocki@...el.com" <rafael.j.wysocki@...el.com>,
	"alan@...ux.intel.com" <alan@...ux.intel.com>,
	"linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"delicious.quinoa@...il.com" <delicious.quinoa@...il.com>,
	"dinguyen@...nsource.altera.com" <dinguyen@...nsource.altera.com>,
	"yvanderv@...nsource.altera.com" <yvanderv@...nsource.altera.com>
Subject: Re: [PATCH 1/2] i2c: designware: device tree bindings for i2c speed
 mode

On Tue, Aug 19, 2014 at 07:34:35PM +0100, atull@...nsource.altera.com wrote:
> From: Alan Tull <atull@...nsource.altera.com>
> 
> Add "speed-mode" Device Tree property to select between
> standard and fast i2c mode.  Previously, driver was hardwired
> as fast mode.  Default to fast mode if property is not
> present.
> 
> Signed-off-by: Alan Tull <atull@...nsource.altera.com>
> ---
>  .../devicetree/bindings/i2c/i2c-designware.txt     |    3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/i2c/i2c-designware.txt b/Documentation/devicetree/bindings/i2c/i2c-designware.txt
> index 5199b0c..0e4cd21 100644
> --- a/Documentation/devicetree/bindings/i2c/i2c-designware.txt
> +++ b/Documentation/devicetree/bindings/i2c/i2c-designware.txt
> @@ -9,6 +9,8 @@ Required properties :
>  Recommended properties :
>  
>   - clock-frequency : desired I2C bus clock frequency in Hz.
> + - speed-mode      : 0 = standard (0 - 100Kb/s)
> +                   : 1 = fast (<= 400Kb/s) <== default

This is a bit opaque.

Is this a limit on the max bit-rate the device should operate at?

Why not just have an optional boolean property to limit to standard
speed?

Thanks,
Mark.

>  
>  Optional properties :
>   - i2c-sda-hold-time-ns : should contain the SDA hold time in nanoseconds.
> @@ -29,6 +31,7 @@ Example :
>  		reg = <0xf0000 0x1000>;
>  		interrupts = <11>;
>  		clock-frequency = <400000>;
> +		speed-mode = <0>;
>  	};
>  
>  	i2c@...0000 {
> -- 
> 1.7.9.5
> 
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