Re: [PATCH v2 06/29] mtd: Add support for reading MTD devices via the nvmem API

[Boris Brezillon]

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

> On 20/08/18 19:20, Boris Brezillon wrote:
> > On Mon, 20 Aug 2018 11:43:34 +0100
> > Srinivas Kandagatla <srinivas.kandagatla@xxxxxxxxxx> 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@0 {
> > 				reg = <0x0 0x14>;
> > 			};
> > 		};
> > 
> > 		partitions {
> > 			compatible = "fixed-partitions";
> > 			#address-cells = <1>;
> > 			#size-cells = <1>;
> > 
> > 			partition@0 {
> > 				reg = <0x0 0x20000>;
> > 
> > 				nvmem-cells {
> > 					#address-cells = <1>;
> > 					#size-cells = <1>;
> > 
> > 					cell@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@0 {
> 			compatible = "nvmem-cell";
> 			reg = <0x0 0x14>;
> 		};
> 
> 		partitions {
> 			compatible = "fixed-partitions";
> 			#address-cells = <1>;
> 			#size-cells = <1>;
> 
> 			partition@0 {
> 				reg = <0x0 0x20000>;
> 				cell@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@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.