On Mon, 16 Nov 2015, Damien Riegel wrote:
> Currently syscon has a fixed configuration of 32 bits for register and
> values widths. In some cases, it would be desirable to be able to
> customize the value width.
>
> For example, certain boards (like the ones manufactured by Technologic
> Systems) have a FPGA that is memory-mapped, but its registers are only
> 16-bit wide.
>
> This patch adds an optional "bus-width" DT binding for syscon that
> allows to change the width for the data bus (i.e. val_bits). If this
> property is provided, it will also adjust the register stride to
> bus-width / 8. If not provided, the default configuration is used.
>
> Signed-off-by: Damien Riegel <damien.riegel@xxxxxxxxxxxxxxxxxxxx>
> ---
> Documentation/devicetree/bindings/mfd/syscon.txt | 3 +++
> drivers/mfd/syscon.c | 12 ++++++++++++
> 2 files changed, 15 insertions(+)
>
> diff --git a/Documentation/devicetree/bindings/mfd/syscon.txt b/Documentation/devicetree/bindings/mfd/syscon.txt
> index fe8150b..4c9d187 100644
> --- a/Documentation/devicetree/bindings/mfd/syscon.txt
> +++ b/Documentation/devicetree/bindings/mfd/syscon.txt
> @@ -13,6 +13,9 @@ Required properties:
> - compatible: Should contain "syscon".
> - reg: the register region can be accessed from syscon
>
> +Optional property:
> +- bus-width: width of the data bus. Can be <8>, <16>, <32>, or <64>.
> +
> Examples:
> gpr: iomuxc-gpr@020e0000 {
> compatible = "fsl,imx6q-iomuxc-gpr", "syscon";
> diff --git a/drivers/mfd/syscon.c b/drivers/mfd/syscon.c
> index 176bf0f..00b0995 100644
> --- a/drivers/mfd/syscon.c
> +++ b/drivers/mfd/syscon.c
> @@ -47,6 +47,7 @@ static struct syscon *of_syscon_register(struct device_node *np)
> struct syscon *syscon;
> struct regmap *regmap;
> void __iomem *base;
> + u32 bus_width;
> int ret;
> struct regmap_config syscon_config = syscon_regmap_config;
>
> @@ -69,6 +70,17 @@ static struct syscon *of_syscon_register(struct device_node *np)
> else if (of_property_read_bool(np, "little-endian"))
> syscon_config.val_format_endian = REGMAP_ENDIAN_LITTLE;
>
> + ret = of_property_read_u32(np, "bus-width", &bus_width);
> + if (!ret) {
This syntax is confusing, as we normally associate it with an error
condition. Instead, I'd use:
if (of_property_read_u32(np, "bus-width", &bus_width) == 0)
Or, for more clarity:
of_property_read_u32(np, "bus-width", &bus_width);
if (bus_width)
If you choose this version (which I think is my preferred method, don't
forget to initialise 'bus_width' to zero.
> + /*
> + * the property has been provided, regmap_init_mmio
> + * will return an error if these values are invalid
> + * so there is no need to check them here.
> + */
> + syscon_config.val_bits = bus_width;
> + syscon_config.reg_stride = syscon_config.val_bits / 8;
> + }
> +
> regmap = regmap_init_mmio(NULL, base, &syscon_config);
> if (IS_ERR(regmap)) {
> pr_err("regmap init failed\n");
--
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
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