rtc: twl: add NVRAM support

Export SRAM using nvmem.
Signed-off-by: Ladislav Michl <ladis@linux-mips.org>
Reviewed-by: Tony Lindgren <tony@atomide.com>
Link: https://lore.kernel.org/r/ZDf7qZTiml0ijD2g@lenochSigned-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

drivers/rtc/rtc-twl.c

@@ -487,11 +487,24 @@ static const struct rtc_class_ops twl_rtc_ops = {
 	.alarm_irq_enable = twl_rtc_alarm_irq_enable,
 };
 
+static int twl_nvram_read(void *priv, unsigned int offset, void *val,
+			  size_t bytes)
+{
+	return twl_i2c_read((long)priv, val, offset, bytes);
+}
+
+static int twl_nvram_write(void *priv, unsigned int offset, void *val,
+			   size_t bytes)
+{
+	return twl_i2c_write((long)priv, val, offset, bytes);
+}
+
 /*----------------------------------------------------------------------*/
 
 static int twl_rtc_probe(struct platform_device *pdev)
 {
 	struct twl_rtc *twl_rtc;
+	struct nvmem_config nvmem_cfg;
 	struct device_node *np = pdev->dev.of_node;
 	int ret = -EINVAL;
 	int irq = platform_get_irq(pdev, 0);
@@ -579,6 +592,30 @@ static int twl_rtc_probe(struct platform_device *pdev)
 		return ret;
 	}
 
+	memset(&nvmem_cfg, 0, sizeof(nvmem_cfg));
+	nvmem_cfg.name = "twl-secured-";
+	nvmem_cfg.type = NVMEM_TYPE_BATTERY_BACKED;
+	nvmem_cfg.reg_read = twl_nvram_read,
+	nvmem_cfg.reg_write = twl_nvram_write,
+	nvmem_cfg.word_size = 1;
+	nvmem_cfg.stride = 1;
+	if (twl_class_is_4030()) {
+		/* 20 bytes SECURED_REG area */
+		nvmem_cfg.size = 20;
+		nvmem_cfg.priv = (void *)TWL_MODULE_SECURED_REG;
+		devm_rtc_nvmem_register(twl_rtc->rtc, &nvmem_cfg);
+		/* 8 bytes BACKUP area */
+		nvmem_cfg.name = "twl-backup-";
+		nvmem_cfg.size = 8;
+		nvmem_cfg.priv = (void *)TWL4030_MODULE_BACKUP;
+		devm_rtc_nvmem_register(twl_rtc->rtc, &nvmem_cfg);
+	} else {
+		/* 8 bytes SECURED_REG area */
+		nvmem_cfg.size = 8;
+		nvmem_cfg.priv = (void *)TWL_MODULE_SECURED_REG;
+		devm_rtc_nvmem_register(twl_rtc->rtc, &nvmem_cfg);
+	}
+
 	return 0;
 }