On Wed, Nov 25, 2015 at 02:32:53PM -0600, Rob Herring wrote:

On Wed, Nov 25, 2015 at 02:25:03PM -0500, Damien Riegel wrote:

quoted

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.

See the 8250 UART bindings. This problem is already solved and has 
standard bindings for it.

Okay, I'll change bus-width to reg-io-width. Are you also suggesting to
use reg-shift to parametrize reg_stride?

Rob

quoted

Signed-off-by: Damien Riegel <redacted>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Lee Jones <redacted>
---
 Documentation/devicetree/bindings/mfd/syscon.txt |  3 +++
 drivers/mfd/syscon.c                             | 13 +++++++++++++
 2 files changed, 16 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 at 020e0000 {
 	compatible = "fsl,imx6q-iomuxc-gpr", "syscon";

diff --git a/drivers/mfd/syscon.c b/drivers/mfd/syscon.c
index 176bf0f..5a93d80 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 +70,18 @@ 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;
 
+	/*
+	 * search for bus-width property in DT. If it is not provided, default
+	 * to 32-bit. regmap_init_mmio will return an error if syscon_config's
+	 * values are invalid so there is no need to check them here.
+	 */
+	ret = of_property_read_u32(np, "bus-width", &bus_width);
+	if (ret)
+		bus_width = 32;
+
+	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");

-- 
2.5.0