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Subject: Re: [PATCH v3 1/3] nvmem: Update the OF binding to use a subnode for
 the cells list
To:     Alban <albeu@free.fr>
Cc:     linux-kernel@vger.kernel.org, Rob Herring <robh+dt@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        David Woodhouse <dwmw2@infradead.org>,
        Brian Norris <computersforpeace@gmail.com>,
        Boris Brezillon <boris.brezillon@free-electrons.com>,
        Marek Vasut <marek.vasut@gmail.com>,
        Richard Weinberger <richard@nod.at>,
        Cyrille Pitchen <cyrille.pitchen@wedev4u.fr>,
        devicetree@vger.kernel.org, linux-mtd@lists.infradead.org
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From:   Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Message-ID: <d30656d6-f17e-6ed0-251f-2b59d02cd202@linaro.org>
Date:   Tue, 1 May 2018 17:49:03 +0100
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On 18/04/18 14:34, Alban wrote:
> On Wed, 18 Apr 2018 13:53:56 +0100
> Srinivas Kandagatla <srinivas.kandagatla@linaro.org> wrote:
> 
>> On 18/04/18 13:32, Alban wrote:
>>>> 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>;
>>>> 		};
>>>> 	};
>>>> };
>>> But the root cause is in the nvmem binding, this conflict could exists
>> No, the root cause is because of passing wrong device instance to nvmem
>> core. And trying to workaround is the actual issue.
> 
> The data is stored on the MTD, so the nvmem provider is the MTD device.
> I don't think it is a good idea to have a virtual device in the DT to
> accommodate the nvmem API.
> 
Yep, I agree! this is same issue if we make nvmem-cells a child of nvmem 
provider too.

However, I would like to see this moving forward.

I can think of one possible solution here, which is, adding 
"nvmem-mtd-cell" or "nvmem-cell" compatible string to each cell. The 
problem you mentioned regarding #address-cells and #size-cells with 
provider need to be addressed in nvmem core.

Currently nvmem core only support offsets of 32 bits, if you are 
expecting a 64 bit offsets then we should add that as a feature to nvmem 
core.

nvmem core as it is today should work fine with 32 bit offsets for mtd 
cases.

what do you think?

thanks,
srini