linux-kernel - Re: [PATCH v6 09/10] dt-binding: mtd: Document gpio-addr-flash

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Date:   Thu, 4 Oct 2018 16:02:07 +0200
From:   Boris Brezillon <boris.brezillon@...tlin.com>
To:     Ricardo Ribalda Delgado <ricardo.ribalda@...il.com>
Cc:     David Woodhouse <dwmw2@...radead.org>,
        Brian Norris <computersforpeace@...il.com>,
        Marek Vasut <marek.vasut@...il.com>,
        Richard Weinberger <richard@....at>,
        Zhouyang Jia <jiazhouyang09@...il.com>,
        linux-mtd@...ts.infradead.org,
        open list <linux-kernel@...r.kernel.org>,
        devicetree@...r.kernel.org
Subject: Re: [PATCH v6 09/10] dt-binding: mtd: Document gpio-addr-flash

On Thu,  4 Oct 2018 15:01:09 +0200
Ricardo Ribalda Delgado <ricardo.ribalda@...il.com> wrote:

> Add documentation for gpio-addr-flash. This binding allow creating
> flash devices that are paged using GPIOs.
> 
> Cc: devicetree@...r.kernel.org
> Reviewed-by: Rob Herring <robh@...nel.org>
> Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@...il.com>
> ---
>  .../bindings/mtd/mtd,gpio-addr-flash.txt      | 25 +++++++++++++++++++
>  1 file changed, 25 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/mtd/mtd,gpio-addr-flash.txt
> 
> diff --git a/Documentation/devicetree/bindings/mtd/mtd,gpio-addr-flash.txt b/Documentation/devicetree/bindings/mtd/mtd,gpio-addr-flash.txt
> new file mode 100644
> index 000000000000..304a33880f9e
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/mtd/mtd,gpio-addr-flash.txt
> @@ -0,0 +1,25 @@
> +Memory Mapped flash with some address lines addressed using GPIOs
> +
> +Handle the case where a flash device is mostly addressed using physical
> +line and supplemented by GPIOs.  This way you can hook up say a 8MiB flash
> +to a 2MiB memory range and use the GPIOs to select a particular range.
> +
> + - compatible :  must be "mtd,gpio-addr-flash", "cfi-flash";

I keep thinking you don't need a specific binding, just add an optional
addr-gpios property to the generic physmap binding and that should do
the trick. Plus, "*mtd*,gpio-addr-flash" is a linux-ism, and DT
bindings should be OS-agnostic.

> + - reg : Address range of the mtd chip that is memory mapped, this is,
> +   on the previous example 2MiB.
> + - addr-gpios: List of GPIO specifiers that will be used to address the MSBs
> +   address lines. The order goes from LSB to MSB.
> +
> +For the rest of the properties, see mtd-physmap.txt.
> +
> +The device tree may optionally contain sub-nodes describing partitions of the
> +address space. Check partition.txt for more details.
> +
> +Example:
> +
> +	flash@...000 {
> +		compatible = "mtd,gpio-addr-flash", "cfi-flash";
> +		bank-width = <2>;
> +		reg = < 0x00300000 0x00200000 >;
> +		addr-gpios = <&gpio_0 3 0>, <&gpio_0 4 0>;
> +	} ;