From mboxrd@z Thu Jan  1 00:00:00 1970
From: boris.brezillon@bootlin.com (Boris Brezillon)
Date: Tue, 21 Aug 2018 11:56:39 +0200
Subject: [PATCH v2 06/29] mtd: Add support for reading MTD devices via
 the nvmem API
In-Reply-To: <e0ec3194-fd3a-9b3d-fba8-f88447eb56e9@linaro.org>
References: <20180810080526.27207-1-brgl@bgdev.pl>
 <20180810080526.27207-7-brgl@bgdev.pl>
 <20180817182720.6a6e5e8e@bbrezillon> <20180819133106.0420df5f@tock>
 <20180819184609.6dcdbb9a@bbrezillon>
 <5b8c30b8-41e1-d59e-542b-fef6c6469ff0@linaro.org>
 <20180820202038.5d3dc195@bbrezillon>
 <e0ec3194-fd3a-9b3d-fba8-f88447eb56e9@linaro.org>
Message-ID: <20180821115639.4894c1c9@bbrezillon>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Tue, 21 Aug 2018 10:50:07 +0100
Srinivas Kandagatla <srinivas.kandagatla@linaro.org> wrote:

> On 20/08/18 19:20, Boris Brezillon wrote:
> > On Mon, 20 Aug 2018 11:43:34 +0100
> > Srinivas Kandagatla <srinivas.kandagatla@linaro.org> wrote:
> >   
> >>
> >> Overall am still not able to clear visualize on how MTD bindings with
> >> nvmem cells would look in both partition and un-partition usecases?
> >> An example DT would be nice here!!  
> > 
> > Something along those lines:
> >   
> This looks good to me.
> > 	mtdnode {
> > 		nvmem-cells {
> > 			#address-cells = <1>;
> > 			#size-cells = <1>;
> > 
> > 			cell at 0 {
> > 				reg = <0x0 0x14>;
> > 			};
> > 		};
> > 
> > 		partitions {
> > 			compatible = "fixed-partitions";
> > 			#address-cells = <1>;
> > 			#size-cells = <1>;
> > 
> > 			partition at 0 {
> > 				reg = <0x0 0x20000>;
> > 
> > 				nvmem-cells {
> > 					#address-cells = <1>;
> > 					#size-cells = <1>;
> > 
> > 					cell at 0 {
> > 						reg = <0x0 0x10>;
> > 					};
> > 				};
> > 			};
> > 		};
> > 	}; >  
> 
> Just curious...Is there a reason why we can't do it like this?:
> Is this because of issue of #address-cells and #size-cells Or mtd 
> bindings always prefer subnodes?
> 
> 	mtdnode {
> 		reg = <0x0123000 0x40000>;
> 		#address-cells = <1>;
> 		#size-cells = <1>;
> 		cell at 0 {
> 			compatible = "nvmem-cell";
> 			reg = <0x0 0x14>;
> 		};
> 
> 		partitions {
> 			compatible = "fixed-partitions";
> 			#address-cells = <1>;
> 			#size-cells = <1>;
> 
> 			partition at 0 {
> 				reg = <0x0 0x20000>;
> 				cell at 0 {
> 					compatible = "nvmem-cell";
> 					reg = <0x0 0x10>;
> 				};
> 			};
> 		};
> 	};

It's because partitions were initially directly defined under the mtd
node, so, if you have an old DT you might have something like:

	mtdnode {
		reg = <0x0123000 0x40000>;
		#address-cells = <1>;
		#size-cells = <1>;

		partition at 0 {
			reg = <0x0 0x20000>;
			...
		};
		...
	};

If we use such a DT with this patch applied, the NVMEM framework will
consider MTD partitions as nvmem cells, which is not what we want.