Re: [PATCH V2 1/2] dt-bindings: mtd: document Broadcom's BCM47xx partitions

[Boris Brezillon <boris.brezillon@bootlin.com>]

On Wed,  9 May 2018 10:17:28 +0200
Rafał Miłecki <zajec5@gmail.com> wrote:

> From: Rafał Miłecki <rafal@milecki.pl>
> 
> Broadcom based home router devices use partitions which have to be
> discovered in a specific way. They are not fixed and there is not any
> standard partition table. This commit adds and describes a new custom
> binding for such devices.
> 
> Signed-off-by: Rafał Miłecki <rafal@milecki.pl>

Applied both.

Thanks,

Boris

> ---
> This commit documents a new binding for describing partitions. Just as a
> reminder: we agreed to use "compatible" for that purpose to avoid
> /guessing/. There are too many cases, devices and /formats/ to just
> blindly try every possible parser.
> 
> This was e.g. described by Boris in his patchset 2+ years ago:
> [RFC PATCH 0/7] mtd: partitions: add of_match_table support
> http://lists.infradead.org/pipermail/linux-mtd/2015-December/064076.html
> 
> Quote:
> >  (2) we can't just scan for all supported parsers (like the block system does), since
> >      there is a wide diversity of "formats" (no standardization), and it is not
> >      always safe or efficient to attempt to do so, particularly since many of
> >      them allow their data structures to be placed anywhere on the flash, and
> >      so require scanning the entire flash device to find them.  
> 
> I believe this solution was also acked back then by Rob:
> [RFC PATCH 3/7] doc: dt: mtd: partition: add on-flash format binding
> http://lists.infradead.org/pipermail/linux-mtd/2015-December/064100.html
> 
> V2: Move documentation to the new brcm,bcm947xx-cfe-partitions.txt file
>     as suggested by Rob (we don't want to bloat partition.txt).
>     Slightly update commit message.
> ---
>  .../devicetree/bindings/mtd/partition.txt          |  2 +-
>  .../partitions/brcm,bcm947xx-cfe-partitions.txt    | 42 ++++++++++++++++++++++
>  2 files changed, 43 insertions(+), 1 deletion(-)
>  create mode 100644 Documentation/devicetree/bindings/mtd/partitions/brcm,bcm947xx-cfe-partitions.txt
> 
> diff --git a/Documentation/devicetree/bindings/mtd/partition.txt b/Documentation/devicetree/bindings/mtd/partition.txt
> index 36f3b769a626..a8f382642ba9 100644
> --- a/Documentation/devicetree/bindings/mtd/partition.txt
> +++ b/Documentation/devicetree/bindings/mtd/partition.txt
> @@ -14,7 +14,7 @@ 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.
>  
> -We currently only document a binding for fixed layouts.
> +Available bindings are listed in the "partitions" subdirectory.
>  
>  
>  Fixed Partitions
> diff --git a/Documentation/devicetree/bindings/mtd/partitions/brcm,bcm947xx-cfe-partitions.txt b/Documentation/devicetree/bindings/mtd/partitions/brcm,bcm947xx-cfe-partitions.txt
> new file mode 100644
> index 000000000000..1d61a029395e
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/mtd/partitions/brcm,bcm947xx-cfe-partitions.txt
> @@ -0,0 +1,42 @@
> +Broadcom BCM47xx Partitions
> +===========================
> +
> +Broadcom is one of hardware manufacturers providing SoCs (BCM47xx) used in
> +home routers. Their BCM947xx boards using CFE bootloader have several partitions
> +without any on-flash partition table. On some devices their sizes and/or
> +meanings can also vary so fixed partitioning can't be used.
> +
> +Discovering partitions on these devices is possible thanks to having a special
> +header and/or magic signature at the beginning of each of them. They are also
> +block aligned which is important for determinig a size.
> +
> +Most of partitions use ASCII text based magic for determining a type. More
> +complex partitions (like TRX with its HDR0 magic) may include extra header
> +containing some details, including a length.
> +
> +A list of supported partitions includes:
> +1) Bootloader with Broadcom's CFE (Common Firmware Environment)
> +2) NVRAM with configuration/calibration data
> +3) Device manufacturer's data with some default values (e.g. SSIDs)
> +4) TRX firmware container which can hold up to 4 subpartitions
> +5) Backup TRX firmware used after failed upgrade
> +
> +As mentioned earlier, role of some partitions may depend on extra configuration.
> +For example both: main firmware and backup firmware use the same TRX format with
> +the same header. To distinguish currently used firmware a CFE's environment
> +variable "bootpartition" is used.
> +
> +
> +Devices using Broadcom partitions described above should should have flash node
> +with a subnode named "partitions" using following properties:
> +
> +Required properties:
> +- compatible : (required) must be "brcm,bcm947xx-cfe-partitions"
> +
> +Example:
> +
> +flash@0 {
> +	partitions {
> +		compatible = "brcm,bcm947xx-cfe-partitions";
> +	};
> +};


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