drivers: spi: it8xxx2: only enable spi clock during spi transaction

To reduce power consumption, the SPI clock is gated when no spi
transaction is in progress. With this mechanism, current
consumption is reduced by approximately 0.1mA when cpu idle.

Signed-off-by: Ren Chen <[email protected]>

Author: Chenhongren

drivers/spi/spi_it8xxx2.c

@@ -61,6 +61,10 @@ LOG_MODULE_REGISTER(spi_it8xxx2, CONFIG_SPI_LOG_LEVEL);
 #define SPI25_CH1_CMD_ADDR_HB2    0x25
 #define SPI27_CH1_WR_MEM_ADDR_HB2 0x27
 
+#define ECPM_BASE_ADDR          DT_REG_ADDR(DT_NODELABEL(ecpm))
+#define ECPM05_CLK_GATING_CTRL3 0x05
+#define SSPI_CLOCK_GATING       BIT(1)
+
 struct spi_it8xxx2_cmdq_data {
 	uint8_t spi_write_cmd_length;
 
@@ -100,6 +104,23 @@ struct spi_it8xxx2_data {
 	size_t receive_len;
 };
 
+static inline void spi_it8xxx2_turn_on_clk(const struct device *dev, const bool enable)
+{
+	ARG_UNUSED(dev);
+
+	uint8_t reg_val;
+	unsigned int key = irq_lock();
+
+	reg_val = sys_read8(ECPM_BASE_ADDR + ECPM05_CLK_GATING_CTRL3);
+	if (enable) {
+		sys_write8(reg_val & ~SSPI_CLOCK_GATING, ECPM_BASE_ADDR + ECPM05_CLK_GATING_CTRL3);
+	} else {
+		sys_write8(reg_val | SSPI_CLOCK_GATING, ECPM_BASE_ADDR + ECPM05_CLK_GATING_CTRL3);
+	}
+
+	irq_unlock(key);
+};
+
 static inline int spi_it8xxx2_set_freq(const struct device *dev, const uint32_t frequency)
 {
 	const struct spi_it8xxx2_config *cfg = dev->config;
@@ -209,11 +230,14 @@ static void spi_it8xxx2_complete(const struct device *dev, const int status)
 	struct spi_it8xxx2_data *data = dev->data;
 	struct spi_context *ctx = &data->ctx;
 
-	spi_context_complete(ctx, dev, status);
-
 	/* Permit to enter power policy and idle mode. */
 	pm_policy_state_lock_put(PM_STATE_STANDBY, PM_ALL_SUBSTATES);
 	chip_permit_idle();
+
+	/* disable spi clock */
+	spi_it8xxx2_turn_on_clk(dev, false);
+
+	spi_context_complete(ctx, dev, status);
 }
 
 static inline void spi_it8xxx2_tx(const struct device *dev)
@@ -400,6 +424,9 @@ static int transceive(const struct device *dev, const struct spi_config *config,
 	chip_block_idle();
 	pm_policy_state_lock_get(PM_STATE_STANDBY, PM_ALL_SUBSTATES);
 
+	/* enable spi clock */
+	spi_it8xxx2_turn_on_clk(dev, true);
+
 	spi_context_buffers_setup(ctx, tx_bufs, rx_bufs, 1);
 	ret = spi_it8xxx2_next_xfer(dev);
 	if (!ret) {