[RFC v2 1/2] dt-bindings: mmc: Document the Amlogic Meson8 and Meson8b SDIO bindings

[Ulf Hansson]

On 24 September 2017 at 21:05, Martin Blumenstingl
<martin.blumenstingl at googlemail.com> wrote:
> From: Carlo Caione <carlo at endlessm.com>
>
> This documents the devicetree bindings for the SDIO/MMC host found in
> Amlogic Meson8 and Meson8b SoCs. It supports the SD specification v2.0
> and the eMMC specification v4.41.
> It has an internal "mux" which allows connecting up to three MMC devices
> to it. The maximum supported bus-width is 4-bits.
>
> Amlogic's GPL kernel sources call it "SDIO" to differentiate it from the
> other MMC controller in (at least the Meson8 and Meson8b) the SoCs (they
> call the other one "SDHC", which supports a bus-width of up to 8-bits).
>
> Signed-off-by: Carlo Caione <carlo at endlessm.com>
> Signed-off-by: Martin Blumenstingl <martin.blumenstingl at googlemail.com>
> ---
>  .../bindings/mmc/amlogic,meson-mx-sdio.txt         | 52 ++++++++++++++++++++++
>  1 file changed, 52 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/mmc/amlogic,meson-mx-sdio.txt
>
> diff --git a/Documentation/devicetree/bindings/mmc/amlogic,meson-mx-sdio.txt b/Documentation/devicetree/bindings/mmc/amlogic,meson-mx-sdio.txt
> new file mode 100644
> index 000000000000..124ea362eec9
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/mmc/amlogic,meson-mx-sdio.txt
> @@ -0,0 +1,52 @@
> +* Amlogic Meson6, Meson8 and Meson8b SDIO/MMC controller
> +
> +The highspeed MMC host controller on Amlogic SoCs provides an interface
> +for MMC, SD, SDIO and SDHC types of memory cards.
> +
> +Supported maximum speeds are the ones of the eMMC standard 4.41 as well
> +as the speed of SD standard 2.0.
> +
> +The hardware provides an internal "mux" which allows up to three slots
> +to be controlled. Only one slot can be accessed at a time.

This is good information, however as the driver won't support multiple
slots, at least short term, I think we need to mention that. Otherwise
people may think that three slots is actually supported, while in fact
it isn't.

> +
> +Required properties:
> + - compatible : must be one of
> +       - "amlogic,meson8-sdio"
> +       - "amlogic,meson8b-sdio"
> +       along with the generic "amlogic,meson-mx-sdio"
> + - reg : mmc controller base registers
> + - interrupts : mmc controller interrupt
> + - #address-cells : must be 1
> + - size-cells : must be 0
> + - clocks : phandle to clock providers
> + - clock-names : must contain "core" and "clkin"
> +
> +Required child nodes:
> +A node for each slot provided by the MMC controller is required.
> +
> +Required properties on each child node (= slot):
> + - compatible : must be "mmc-slot" (see mmc.txt within this directory)
> + - reg : the slot (or "port") ID
> +
> +Optional properties on each child node (= slot):
> + - bus-width : must be 1 or 4 (8-bit bus is not supported)
> + - for cd and all other additional generic mmc parameters
> +   please refer to mmc.txt within this directory
> +
> +Examples:
> +       mmc at c1108c20 {
> +               compatible = "amlogic,meson8-sdio", "amlogic,meson-mx-sdio";
> +               reg = <0xc1108c20 0x20>;
> +               interrupts = <0 28 1>;
> +               #address-cells = <1>;
> +               #size-cells = <0>;
> +               clocks = <&clkc CLKID_SDIO>, <&clkc CLKID_CLK81>;
> +               clock-names = "core", "clkin";
> +
> +               slot at 1 {
> +                       compatible = "mmc-slot";
> +                       reg = <1>;
> +
> +                       bus-width = <4>;
> +               };
> +       };
> --
> 2.14.1
>

Kind regards
Uffe