[PATCH v2 2/2] rtc: rtc7301: Support byte-addressed IO

[Linus Walleij <linus.walleij@linaro.org>]

The old RTC7301 driver in OpenWrt used byte access, but the
current mainline Linux driver uses 32bit word access.

Make this configurable using device properties using the
standard property "reg-io-width" in e.g. device tree.

This is needed for the USRobotics USR8200 which has the
chip connected using byte accesses.

Debugging and testing by Howard Harte.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
---
 drivers/rtc/rtc-r7301.c | 35 +++++++++++++++++++++++++++++++++--
 1 file changed, 33 insertions(+), 2 deletions(-)

diff --git a/drivers/rtc/rtc-r7301.c b/drivers/rtc/rtc-r7301.c
index 5dbaeb7af648..ef913cf8593f 100644
--- a/drivers/rtc/rtc-r7301.c
+++ b/drivers/rtc/rtc-r7301.c
@@ -14,6 +14,7 @@
 #include <linux/module.h>
 #include <linux/mod_devicetable.h>
 #include <linux/delay.h>
+#include <linux/property.h>
 #include <linux/regmap.h>
 #include <linux/platform_device.h>
 #include <linux/rtc.h>
@@ -55,12 +56,23 @@ struct rtc7301_priv {
 	u8 bank;
 };
 
-static const struct regmap_config rtc7301_regmap_config = {
+/*
+ * When the device is memory-mapped, some platforms pack the registers into
+ * 32-bit access using the lower 8 bits at each 4-byte stride, while others
+ * expose them as simply consecutive bytes.
+ */
+static const struct regmap_config rtc7301_regmap_32_config = {
 	.reg_bits = 32,
 	.val_bits = 8,
 	.reg_stride = 4,
 };
 
+static const struct regmap_config rtc7301_regmap_8_config = {
+	.reg_bits = 8,
+	.val_bits = 8,
+	.reg_stride = 1,
+};
+
 static u8 rtc7301_read(struct rtc7301_priv *priv, unsigned int reg)
 {
 	int reg_stride = regmap_get_reg_stride(priv->regmap);
@@ -356,7 +368,9 @@ static int __init rtc7301_rtc_probe(struct platform_device *dev)
 	void __iomem *regs;
 	struct rtc7301_priv *priv;
 	struct rtc_device *rtc;
+	static const struct regmap_config *mapconf;
 	int ret;
+	u32 val;
 
 	priv = devm_kzalloc(&dev->dev, sizeof(*priv), GFP_KERNEL);
 	if (!priv)
@@ -366,8 +380,25 @@ static int __init rtc7301_rtc_probe(struct platform_device *dev)
 	if (IS_ERR(regs))
 		return PTR_ERR(regs);
 
+	ret = device_property_read_u32(&dev->dev, "reg-io-width", &val);
+	if (ret)
+		/* Default to 32bit accesses */
+		val = 4;
+
+	switch (val) {
+	case 1:
+		mapconf = &rtc7301_regmap_8_config;
+		break;
+	case 4:
+		mapconf = &rtc7301_regmap_32_config;
+		break;
+	default:
+		dev_err(&dev->dev, "invalid reg-io-width %d\n", val);
+		return -EINVAL;
+	}
+
 	priv->regmap = devm_regmap_init_mmio(&dev->dev, regs,
-					     &rtc7301_regmap_config);
+					     mapconf);
 	if (IS_ERR(priv->regmap))
 		return PTR_ERR(priv->regmap);
 

-- 
2.41.0