Re: [PATCH v2 2/2] doc: dt: mtd: add a DT property to enable the use of 4byte-address op codes

[Rob Herring]

On Tue, Mar 22, 2016 at 10:13 AM, Cyrille Pitchen
<cyrille.pitchen@xxxxxxxxx> wrote:
> This patch adds a new optional DT property which enables an alternative
> way of supporting memory size above 16MiB (128Mib). This new mechanism
> translates the regular 3byte-address op codes into their 4byte-address
> version whereas the old/default mecanism makes the SPI memory enter its
> 4byte-address mode, which has annoying side effects for early bootloaders.
>
> We cannot discover at run time whether the SPI NOR memory supports the
> 4byte-address op codes. For instance both Macronix MX25L25635E and
> MX25L25673G share the same JEDEC ID (C22019 without any extension byte).
> However the first one doesn't support 4byte-address op codes whereas the
> second one does.
>
> Signed-off-by: Cyrille Pitchen <cyrille.pitchen@xxxxxxxxx>
> ---
>  Documentation/devicetree/bindings/mtd/jedec,spi-nor.txt | 11 +++++++++++
>  1 file changed, 11 insertions(+)
>
> diff --git a/Documentation/devicetree/bindings/mtd/jedec,spi-nor.txt b/Documentation/devicetree/bindings/mtd/jedec,spi-nor.txt
> index 2c91c03e7eb0..8be610482089 100644
> --- a/Documentation/devicetree/bindings/mtd/jedec,spi-nor.txt
> +++ b/Documentation/devicetree/bindings/mtd/jedec,spi-nor.txt
> @@ -66,6 +66,17 @@ Optional properties:
>                     Refer to your chips' datasheet to check if this is supported
>                     by your chip.
>
> +- m25p,4byte-opcodes: For memory size above 16MiB (128Mib), use the dedicated

m25p is not a vendor. So drop it or m25p-4byte-opcodes.

> +                      4byte-address opcodes instead of entering the 4byte
> +                      address mode. This mode changes the internal state of the
> +                      chip so may conflict with some early boot loaders, which
> +                      expect to use the regular (Fast) Read opcodes with 3byte
> +                      address.
> +                      However 4byte-address opcodes are not supported by all
> +                      chips and support for them can not be detected at runtime.

s/can not/cannot/

> +                      Refer to you chip's datasheet to check if this is
> +                      supported by your chip.
> +
>  Example:
>
>         flash: m25p80@0 {
> --
> 1.8.2.2
>