linux-kernel - Re: [PATCH v3 1/3] nvmem: Update the OF binding to use a subnode for the cells list

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Date:   Wed, 18 Apr 2018 13:12:48 +0100
From:   Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
To:     Alban <albeu@...e.fr>
Cc:     linux-kernel@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        David Woodhouse <dwmw2@...radead.org>,
        Brian Norris <computersforpeace@...il.com>,
        Boris Brezillon <boris.brezillon@...e-electrons.com>,
        Marek Vasut <marek.vasut@...il.com>,
        Richard Weinberger <richard@....at>,
        Cyrille Pitchen <cyrille.pitchen@...ev4u.fr>,
        devicetree@...r.kernel.org, linux-mtd@...ts.infradead.org
Subject: Re: [PATCH v3 1/3] nvmem: Update the OF binding to use a subnode for
 the cells list



On 18/04/18 12:41, Alban wrote:
> On Tue, 17 Apr 2018 18:00:40 +0200
> Alban <albeu@...e.fr> wrote:
> 
>> On Tue, 17 Apr 2018 16:44:01 +0100
>> Srinivas Kandagatla <srinivas.kandagatla@...aro.org> wrote:
>>
>>> Thanks for explaining,
>>>
>>> On 17/04/18 15:54, Alban wrote:
>>>> This will not only allow reading the calibration data from nvmem, but
>>>> will also create a partition on the MTD device, which is not acceptable.
>>>> With my proposed binding this would become:
>>>>
>>>> flash@0 {
>>>> 	#address-cells = <1>;
>>>> 	#size-cells = <1>;
>>>> 	compatible = "s25sl064a";
>>>> 	reg = <0>;
>>>>
>>>> 	nvmem-cells {
>>>> 		compatible = "nvmem-cells";
>>>> 		#address-cells = <1>;
>>>> 		#address-cells = <1>;
>>>>
>>>> 		calibration: calib@404 {
>>>> 			reg = <0x404 0x10>;
>>>> 		};
>>>> 	};
>>>
>>> Why can't we make nvmem-cells node a nvmem provider in this case?
>>> Which should work!
>>
>> TBH I just copied what have been done to fix the same problem with the
>> MTD partitions. But yes we could also just extend the current binding
>> to require a compatible string on each nvmem-cell, which would not
>> require any code change to support.
> 
> However this scheme will not work if the device node binding already
> have subnodes with addresses. The addressing, as specified by
> #address-cells and #size-cells, might be incompatible or might overlap.
> Using the nvmem-cells subnode solve this problem.
> 

I was also suggesting you to use nvmem-cell subnode, but make it a 
proper nvmem provider device, rather than reusing its parent device.

You would end up some thing like this in dt.

flash@0 {
	#address-cells = <1>;
	#size-cells = <1>;
	compatible = "s25sl064a";
	reg = <0>;

	nvmem-cells {
		compatible = "mtd-nvmem";
		#address-cells = <1>;
		#size-cells = <1>;

		calibration: calib@404 {
			reg = <0x404 0x10>;
		};
	};
};

--srini

> Alban
>