generic: RTC7301 byte-addressed IO

This is a backport of the patch for byte addressed IO to the
Epson RTC7301 driver. This is used by the IXP4xx-based
USRobotics USR8200.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

diff --git a/target/linux/generic/backport-6.1/831-v6.7-rtc-rtc7301-Support-byte-addressed-IO.patch b/target/linux/generic/backport-6.1/831-v6.7-rtc-rtc7301-Support-byte-addressed-IO.patch
new file mode 100644 (file)
index 0000000..ddda6e4
--- /dev/null
+++ b/target/linux/generic/backport-6.1/831-v6.7-rtc-rtc7301-Support-byte-addressed-IO.patch
@@ -0,0 +1,93 @@
+From edd25a77e69b7c546c28077e5dffe72c54c0afe8 Mon Sep 17 00:00:00 2001
+From: Linus Walleij <linus.walleij@linaro.org>
+Date: Thu, 21 Sep 2023 22:18:12 +0200
+Subject: [PATCH 2/4] rtc: rtc7301: Support byte-addressed IO
+
+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(-)
+
+--- 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(stru
+       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(stru
+       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);
+