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

From: Alban <albeu@free.fr>
To: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Cc: Alban <albeu@free.fr>,
	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
Subject: Re: [PATCH v3 1/3] nvmem: Update the OF binding to use a subnode for the cells list
Date: Wed, 18 Apr 2018 14:32:43 +0200	[thread overview]
Message-ID: <20180418143243.3c23493c@avionic-0020> (raw)
In-Reply-To: <9f7d2987-b33e-79b5-ae58-2985fd7334e4@linaro.org>

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On Wed, 18 Apr 2018 13:12:48 +0100
Srinivas Kandagatla <srinivas.kandagatla@linaro.org> wrote:

> On 18/04/18 12:41, Alban wrote:
> > On Tue, 17 Apr 2018 18:00:40 +0200
> > Alban <albeu@free.fr> wrote:
> >   
> >> On Tue, 17 Apr 2018 16:44:01 +0100
> >> Srinivas Kandagatla <srinivas.kandagatla@linaro.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>;
> 		};
> 	};
> };

But the root cause is in the nvmem binding, this conflict could exists
with any device type, not just MTD. I don't understand why we would want
such workarounds instead of just fixing the problem once and for all.

Alban

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