Re: [PATCH 1/2] dt-bindings: mtd: explicitly describe nesting partitions

[Rob Herring <robh@kernel.org>]

On Wed, May 23, 2018 at 07:14:47PM +0200, Rafał Miłecki wrote:
> From: Rafał Miłecki <rafal@milecki.pl>
> 
> Documentation was already saying that fixed and dynamic partitioning can
> be mixed but was missing a clear description and examples. This commit
> adds a proper description of how partitions can be nested and how layout
> descriptions can be mixed.
> 
> This addition is important for partitions that contain subpartitions.
> It's useful to have parent partition registered (e.g. for overwriting
> purposes) as well as children ones (for accessing data). It's also
> required when a single partition uses different partitioning method
> (e.g. vendor custom "firmware" partition with kernel + rootfs).
> 
> Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
> ---
> Another example (I couldn't put in Documentation yet) could be:
> 
> flash@0 {
> 	partitions {
> 		compatible = "fixed-partitions";
> 		#address-cells = <1>;
> 		#size-cells = <1>;
> 
> 		partition@0 {
> 			label = "bootloader";
> 			reg = <0x0000000 0x0100000>;
> 			read-only;
> 		};
> 
> 		firmware@100000 {
> 			label = "firmware";
> 			reg = <0x0100000 0x0800000>;
> 			compatible = "brcm,trx";
> 		};
> 	};
> };
> 
> It's probably even more realistic one, but we don't describe "brcm,trx"
> binding yet.

This one makes more sense to me than the one you've added because if you 
only have fixed partitions, it seems like most times you could just 
flatten them to 1 level. I suppose having some levels could make doing 
updates easier.

> The purpose of above description would be to:
> 1) Specify fixed partitions (they never change)
> 2) Tell operating system that "firmware" partition uses Broadcom's TRX
>    format which is a container for 2 or 3 subpartitions (usually: kernel
>    and rootfs).
> ---
>  .../devicetree/bindings/mtd/partition.txt          | 25 ++++++++++++++++++++++
>  1 file changed, 25 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/mtd/partition.txt b/Documentation/devicetree/bindings/mtd/partition.txt
> index a8f382642ba9..2214167ce88a 100644
> --- a/Documentation/devicetree/bindings/mtd/partition.txt
> +++ b/Documentation/devicetree/bindings/mtd/partition.txt
> @@ -14,6 +14,13 @@ method is used for a given flash device. To describe the method there should be
>  a subnode of the flash device that is named 'partitions'. It must have a
>  'compatible' property, which is used to identify the method to use.
>  
> +When a single partition is represented with a DT node (it depends on a used
> +format) it may also be described using above rules ('compatible' and optionally
> +some extra properties / subnodes). It allows describing more complex,
> +hierarchical (multi-level) layouts and should be used if there is some
> +significant relation between partitions or some partition internally uses
> +another partitioning method.
> +
>  Available bindings are listed in the "partitions" subdirectory.
>  
>  
> @@ -73,6 +80,24 @@ flash@0 {
>  		uimage@100000 {
>  			reg = <0x0100000 0x200000>;
>  		};
> +
> +		calibration@200000 {
> +			label = "calibration";
> +			reg = <0x0200000 0x100000>;
> +			compatible = "fixed-partitions";
> +			#address-cells = <1>;
> +			#size-cells = <1>;

You are missing 'ranges' here.

> +
> +			partition@0 {
> +				label = "wifi0";
> +				reg = <0x000000 0x080000>;
> +			};
> +
> +			partition@80000 {
> +				label = "wifi1";
> +				reg = <0x080000 0x080000>;
> +			};
> +		};
>  	};
>  };
>  
> -- 
> 2.13.6
> 

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