rtc: s35390a: implement nvmem support

This RTC has one "free" register which can be used to store arbitrary
data. Expose it as a nvmem resource in Linux.

Signed-off-by: Lorenz Brun <lorenz@monogon.tech>
Link: https://patch.msgid.link/20251223125728.346073-1-lorenz@monogon.tech
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

diff --git a/drivers/rtc/rtc-s35390a.c b/drivers/rtc/rtc-s35390a.c
index 07bd983b569296b3ec7decb52a0c402e464be914..a4678d7c6cf63836202650dfc8ccf790ff7de2bd 100644 (file)
--- a/drivers/rtc/rtc-s35390a.c
+++ b/drivers/rtc/rtc-s35390a.c
@@ -18,6 +18,7 @@
 #define S35390A_CMD_TIME1      2
 #define S35390A_CMD_TIME2      3
 #define S35390A_CMD_INT2_REG1  5
+#define S35390A_CMD_FREE_REG    7
 
 #define S35390A_BYTE_YEAR      0
 #define S35390A_BYTE_MONTH     1
@@ -416,6 +417,23 @@ static const struct rtc_class_ops s35390a_rtc_ops = {
        .ioctl          = s35390a_rtc_ioctl,
 };
 
+static int s35390a_nvmem_read(void *priv, unsigned int offset, void *val,
+                             size_t bytes)
+{
+       struct s35390a *s35390a = priv;
+
+       /* The offset is ignored because the NVMEM region is only 1 byte */
+       return s35390a_get_reg(s35390a, S35390A_CMD_FREE_REG, val, bytes);
+}
+
+static int s35390a_nvmem_write(void *priv, unsigned int offset, void *val,
+                              size_t bytes)
+{
+       struct s35390a *s35390a = priv;
+
+       return s35390a_set_reg(s35390a, S35390A_CMD_FREE_REG, val, bytes);
+}
+
 static int s35390a_probe(struct i2c_client *client)
 {
        int err, err_read;
@@ -424,6 +442,15 @@ static int s35390a_probe(struct i2c_client *client)
        struct rtc_device *rtc;
        u8 buf, status1;
        struct device *dev = &client->dev;
+       struct nvmem_config nvmem_cfg = {
+               .name = "s35390a_nvram",
+               .type = NVMEM_TYPE_BATTERY_BACKED,
+               .word_size = 1,
+               .stride = 1,
+               .size = 1,
+               .reg_read = s35390a_nvmem_read,
+               .reg_write = s35390a_nvmem_write,
+       };
 
        if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C))
                return -ENODEV;
@@ -490,6 +517,11 @@ static int s35390a_probe(struct i2c_client *client)
        if (status1 & S35390A_FLAG_INT2)
                rtc_update_irq(rtc, 1, RTC_AF);
 
+       nvmem_cfg.priv = s35390a;
+       err = devm_rtc_nvmem_register(rtc, &nvmem_cfg);
+       if (err)
+               return err;
+
        return devm_rtc_register_device(rtc);
 }