[PATCH 2/2] rtc: mt6397: provide the 32 kHz output as a clock

[Ryan Brue]

The RTC's 32 kHz output is gated by RTC_CON.F32KOB, which the vendor
kernel clears before it powers the Wi-Fi/Bluetooth combo chip. Mainline
never touches it, so on a board whose bootloader leaves it set, such a
chip has no sleep clock and does not come up.

Register the output as a clock when the RTC node has #clock-cells, so
the chip's power sequence can enable it.

Signed-off-by: Ryan Brue <ryanbrue.dev at gmail.com>
---
 drivers/rtc/rtc-mt6397.c       | 85 ++++++++++++++++++++++++++++++++++++++++++
 include/linux/mfd/mt6397/rtc.h |  6 +++
 2 files changed, 91 insertions(+)

diff --git a/drivers/rtc/rtc-mt6397.c b/drivers/rtc/rtc-mt6397.c
index d6e156516aa6..5130fecffa7b 100644
--- a/drivers/rtc/rtc-mt6397.c
+++ b/drivers/rtc/rtc-mt6397.c
@@ -6,6 +6,7 @@
 
 #include <linux/array_size.h>
 #include <linux/bitfield.h>
+#include <linux/clk-provider.h>
 #include <linux/err.h>
 #include <linux/interrupt.h>
 #include <linux/mfd/mt6397/core.h>
@@ -317,6 +318,84 @@ static int mtk_rtc_nvram_write(void *priv, unsigned int offset, void *val,
 	return ret;
 }
 
+#ifdef CONFIG_COMMON_CLK
+static int mtk_rtc_clkout_set(struct clk_hw *hw, bool on)
+{
+	struct mt6397_rtc *rtc = container_of(hw, struct mt6397_rtc, clkout);
+	int ret;
+
+	mutex_lock(&rtc->lock);
+	ret = regmap_update_bits(rtc->regmap, rtc->addr_base + rtc->data->con,
+				 RTC_CON_F32KOB, on ? 0 : RTC_CON_F32KOB);
+	if (!ret)
+		ret = mtk_rtc_write_trigger(rtc);
+	mutex_unlock(&rtc->lock);
+
+	return ret;
+}
+
+static int mtk_rtc_clkout_prepare(struct clk_hw *hw)
+{
+	return mtk_rtc_clkout_set(hw, true);
+}
+
+static void mtk_rtc_clkout_unprepare(struct clk_hw *hw)
+{
+	mtk_rtc_clkout_set(hw, false);
+}
+
+static int mtk_rtc_clkout_is_prepared(struct clk_hw *hw)
+{
+	struct mt6397_rtc *rtc = container_of(hw, struct mt6397_rtc, clkout);
+	u32 con;
+
+	if (regmap_read(rtc->regmap, rtc->addr_base + rtc->data->con, &con))
+		return 0;
+
+	return !(con & RTC_CON_F32KOB);
+}
+
+static unsigned long mtk_rtc_clkout_recalc_rate(struct clk_hw *hw,
+						unsigned long parent_rate)
+{
+	return 32768;
+}
+
+static const struct clk_ops mtk_rtc_clkout_ops = {
+	.prepare = mtk_rtc_clkout_prepare,
+	.unprepare = mtk_rtc_clkout_unprepare,
+	.is_prepared = mtk_rtc_clkout_is_prepared,
+	.recalc_rate = mtk_rtc_clkout_recalc_rate,
+};
+
+/* The 32 kHz output the PMIC drives to other chips, such as a combo chip */
+static int mtk_rtc_register_clkout(struct device *dev, struct mt6397_rtc *rtc)
+{
+	struct clk_init_data init = {
+		.name = "mt6397-rtc-32k",
+		.ops = &mtk_rtc_clkout_ops,
+	};
+	int ret;
+
+	if (!rtc->data->con || !of_property_present(dev->of_node, "#clock-cells"))
+		return 0;
+
+	rtc->clkout.init = &init;
+
+	ret = devm_clk_hw_register(dev, &rtc->clkout);
+	if (ret)
+		return ret;
+
+	return devm_of_clk_add_hw_provider(dev, of_clk_hw_simple_get,
+					   &rtc->clkout);
+}
+#else
+static int mtk_rtc_register_clkout(struct device *dev, struct mt6397_rtc *rtc)
+{
+	return 0;
+}
+#endif
+
 static int mtk_rtc_probe(struct platform_device *pdev)
 {
 	struct resource *res;
@@ -380,6 +459,11 @@ static int mtk_rtc_probe(struct platform_device *pdev)
 	if (ret)
 		return ret;
 
+	ret = mtk_rtc_register_clkout(&pdev->dev, rtc);
+	if (ret)
+		return dev_err_probe(&pdev->dev, ret,
+				     "failed to register the 32k clock\n");
+
 	nvmem_cfg.priv = rtc;
 
 	return devm_rtc_nvmem_register(rtc->rtc_dev, &nvmem_cfg);
@@ -416,6 +500,7 @@ static const struct mtk_rtc_data mt6358_rtc_data = {
 
 static const struct mtk_rtc_data mt6397_rtc_data = {
 	.wrtgr = RTC_WRTGR_MT6397,
+	.con = RTC_CON_MT6397,
 };
 
 static const struct of_device_id mt6397_rtc_of_match[] = {
diff --git a/include/linux/mfd/mt6397/rtc.h b/include/linux/mfd/mt6397/rtc.h
index f4da579ec638..a8130d726c59 100644
--- a/include/linux/mfd/mt6397/rtc.h
+++ b/include/linux/mfd/mt6397/rtc.h
@@ -9,6 +9,7 @@
 #ifndef _LINUX_MFD_MT6397_RTC_H_
 #define _LINUX_MFD_MT6397_RTC_H_
 
+#include <linux/clk-provider.h>
 #include <linux/jiffies.h>
 #include <linux/mutex.h>
 #include <linux/regmap.h>
@@ -22,6 +23,9 @@
 #define RTC_WRTGR_MT6397       0x003c
 #define RTC_WRTGR_MT6323       RTC_WRTGR_MT6397
 
+#define RTC_CON_MT6397         0x003e
+#define RTC_CON_F32KOB         BIT(5)
+
 #define RTC_IRQ_STA            0x0002
 #define RTC_IRQ_STA_AL         BIT(0)
 #define RTC_IRQ_STA_LP         BIT(3)
@@ -72,6 +76,7 @@
 
 struct mtk_rtc_data {
 	u32                     wrtgr;
+	u32                     con;
 };
 
 struct mt6397_rtc {
@@ -83,6 +88,7 @@ struct mt6397_rtc {
 	int                     irq;
 	u32                     addr_base;
 	const struct mtk_rtc_data *data;
+	struct clk_hw           clkout;
 };
 
 #endif /* _LINUX_MFD_MT6397_RTC_H_ */

-- 
2.55.0