drivers: spi_nor: support deep-power-down mode

Add internal API to enter and exit deep power-down mode.  Add Kconfig
option to return to DPD whenever device is not active.

When device power management becomes more mature it should be possible
to implement it, which would allow use of DPD without having to enter
and exit DPD between consecutive transactions.

Signed-off-by: Peter A. Bigot <[email protected]>

Author: pabigot

drivers/flash/Kconfig.nor

@@ -31,4 +31,16 @@ config SPI_NOR_FLASH_LAYOUT_PAGE_SIZE
 	  size (65536).  Other options include the 32K-byte erase size
 	  (32768), and the sector size (4096).
 
+config SPI_NOR_IDLE_IN_DPD
+	bool "Use Deep Power-Down mode when flash is not being accessed."
+	help
+	  Where supported deep power-down mode can reduce current draw
+	  to as little as 0.1% of standby current.  However it takes
+	  some milliseconds to enter and exit from this mode.
+
+	  Select this option for applications where device power
+	  management is not enabled, the flash remains inactive for
+	  long periods, and when used the impact of waiting for mode
+	  enter and exit delays is acceptable.
+
 endif # SPI_NOR

drivers/flash/spi_nor.c

@@ -18,8 +18,44 @@
 
 LOG_MODULE_REGISTER(spi_nor, CONFIG_FLASH_LOG_LEVEL);
 
+/* Device Power Management Notes
+ *
+ * These flash devices have several modes during operation:
+ * * When CSn is asserted (during a SPI operation) the device is
+ *   active.
+ * * When CSn is deasserted the device enters a standby mode.
+ * * Some devices support a Deep Power-Down mode which reduces current
+ *   to as little as 0.1% of standby.
+ *
+ * The power reduction from DPD is sufficent to warrant allowing its
+ * use even in cases where Zephyr's device power management is not
+ * available.  This is selected through the SPI_NOR_IDLE_IN_DPD
+ * Kconfig option.
+ *
+ * When mapped to the Zephyr Device Power Management states:
+ * * DEVICE_PM_ACTIVE_STATE covers both active and standby modes;
+ * * DEVICE_PM_LOW_POWER_STATE, DEVICE_PM_SUSPEND_STATE, and
+ *   DEVICE_PM_OFF_STATE all correspond to deep-power-down mode.
+ */
+
 #define SPI_NOR_MAX_ADDR_WIDTH 4
 
+#ifndef NSEC_PER_MSEC
+#define NSEC_PER_MSEC (NSEC_PER_USEC * USEC_PER_MSEC)
+#endif
+
+#ifdef DT_INST_0_JEDEC_SPI_NOR_T_ENTER_DPD
+#define T_DP_MS ceiling_fraction(DT_INST_0_JEDEC_SPI_NOR_T_ENTER_DPD, NSEC_PER_MSEC)
+#endif /* T_ENTER_DPD */
+#ifdef DT_INST_0_JEDEC_SPI_NOR_T_EXIT_DPD
+#define T_RES1_MS ceiling_fraction(DT_INST_0_JEDEC_SPI_NOR_T_EXIT_DPD, NSEC_PER_MSEC)
+#endif /* T_EXIT_DPD */
+#ifdef DT_INST_0_JEDEC_SPI_NOR_DPD_WAKEUP_SEQUENCE
+#define T_DPDD_MS ceiling_fraction(DT_INST_0_JEDEC_SPI_NOR_DPD_WAKEUP_SEQUENCE_0, NSEC_PER_MSEC)
+#define T_CRDP_MS ceiling_fraction(DT_INST_0_JEDEC_SPI_NOR_DPD_WAKEUP_SEQUENCE_1, NSEC_PER_MSEC)
+#define T_RDP_MS ceiling_fraction(DT_INST_0_JEDEC_SPI_NOR_DPD_WAKEUP_SEQUENCE_2, NSEC_PER_MSEC)
+#endif /* DPD_WAKEUP_SEQUENCE */
+
 /**
  * struct spi_nor_data - Structure for defining the SPI NOR access
  * @spi: The SPI device
@@ -33,9 +69,59 @@ struct spi_nor_data {
 #ifdef DT_INST_0_JEDEC_SPI_NOR_CS_GPIOS_CONTROLLER
 	struct spi_cs_control cs_ctrl;
 #endif /* DT_INST_0_JEDEC_SPI_NOR_CS_GPIOS_CONTROLLER */
+#ifdef DT_INST_0_JEDEC_SPI_NOR_HAS_DPD
+	/* Low 32-bits of uptime counter at which device last entered
+	 * deep power-down.
+	 */
+	u32_t ts_enter_dpd;
+#endif
 	struct k_sem sem;
 };
 
+/* Capture the time at which the device entered deep power-down. */
+static inline void record_entered_dpd(const struct device *const dev)
+{
+#ifdef DT_INST_0_JEDEC_SPI_NOR_HAS_DPD
+	struct spi_nor_data *const driver_data = dev->driver_data;
+
+	driver_data->ts_enter_dpd = k_uptime_get_32();
+#endif
+}
+
+/* Check the current time against the time DPD was entered and delay
+ * until it's ok to initiate the DPD exit process.
+ */
+static inline void delay_until_exit_dpd_ok(const struct device *const dev)
+{
+#ifdef DT_INST_0_JEDEC_SPI_NOR_HAS_DPD
+	struct spi_nor_data *const driver_data = dev->driver_data;
+	s32_t since = (s32_t)(k_uptime_get_32() - driver_data->ts_enter_dpd);
+
+	/* If the time is negative the 32-bit counter has wrapped,
+	 * which is certainly long enough no further delay is
+	 * required.  Otherwise we have to check whether it's been
+	 * long enough.
+	 */
+	if (since >= 0) {
+#ifdef DT_INST_0_JEDEC_SPI_NOR_T_ENTER_DPD
+		/* Subtract time required for DPD to be reached */
+		since -= T_DP_MS;
+#endif /* T_ENTER_DPD */
+#ifdef DT_INST_0_JEDEC_SPI_NOR_DPD_WAKEUP_SEQUENCE
+		/* Subtract time required in DPD before exit */
+		since -= T_DPDD_MS;
+#endif /* DT_INST_0_JEDEC_SPI_NOR_DPD_WAKEUP_SEQUENCE */
+
+		/* If the adjusted time is negative we have to wait
+		 * until it reaches zero before we can proceed.
+		 */
+		if (since < 0) {
+			k_sleep(K_MSEC((u32_t)-since));
+		}
+	}
+#endif /* DT_INST_0_JEDEC_SPI_NOR_HAS_DPD */
+}
+
 /*
  * @brief Send an SPI command
  *
@@ -99,9 +185,56 @@ static int spi_nor_access(const struct device *const dev,
 #define spi_nor_cmd_addr_write(dev, opcode, addr, src, length) \
 	spi_nor_access(dev, opcode, true, addr, (void *)src, length, true)
 
+static int enter_dpd(const struct device *const dev)
+{
+	int ret = 0;
+
+	if (IS_ENABLED(DT_INST_0_JEDEC_SPI_NOR_HAS_DPD)) {
+		ret = spi_nor_cmd_write(dev, SPI_NOR_CMD_DPD);
+		if (ret == 0) {
+			record_entered_dpd(dev);
+		}
+	}
+	return ret;
+}
+
+static int exit_dpd(const struct device *const dev)
+{
+	int ret = 0;
+
+	if (IS_ENABLED(DT_INST_0_JEDEC_SPI_NOR_HAS_DPD)) {
+		delay_until_exit_dpd_ok(dev);
+
+#ifdef DT_INST_0_JEDEC_SPI_NOR_DPD_WAKEUP_SEQUENCE
+		/* Assert CSn and wait for tCRDP.
+		 *
+		 * Unfortunately the SPI API doesn't allow us to
+		 * control CSn so fake it by writing a known-supported
+		 * single-byte command, hoping that'll hold the assert
+		 * long enough.  This is highly likely, since the
+		 * duration is usually less than two SPI clock cycles.
+		 */
+		ret = spi_nor_cmd_write(dev, SPI_NOR_CMD_RDID);
+
+		/* Deassert CSn and wait for tRDP */
+		k_sleep(K_MSEC(T_RDP_MS));
+#else /* DPD_WAKEUP_SEQUENCE */
+		ret = spi_nor_cmd_write(dev, SPI_NOR_CMD_RDPD);
+
+		if (ret == 0) {
+#ifdef DT_INST_0_JEDEC_SPI_NOR_T_EXIT_DPD
+			k_sleep(K_MSEC(T_RES1_MS));
+#endif /* T_EXIT_DPD */
+		}
+#endif /* DPD_WAKEUP_SEQUENCE */
+	}
+	return ret;
+}
+
 /* Everything necessary to acquire owning access to the device.
  *
- * For now this means taking the lock.
+ * This means taking the lock and, if necessary, waking the device
+ * from deep power-down mode.
  */
 static void acquire_device(struct device *dev)
 {
@@ -110,14 +243,23 @@ static void acquire_device(struct device *dev)
 
 		k_sem_take(&driver_data->sem, K_FOREVER);
 	}
+
+	if (IS_ENABLED(CONFIG_SPI_NOR_IDLE_IN_DPD)) {
+		exit_dpd(dev);
+	}
 }
 
 /* Everything necessary to release access to the device.
  *
- * For now, this means releasing the lock.
+ * This means (optionally) putting the device into deep power-down
+ * mode, and releasing the lock.
  */
 static void release_device(struct device *dev)
 {
+	if (IS_ENABLED(CONFIG_SPI_NOR_IDLE_IN_DPD)) {
+		enter_dpd(dev);
+	}
+
 	if (IS_ENABLED(CONFIG_MULTITHREADING)) {
 		struct spi_nor_data *const driver_data = dev->driver_data;
 
@@ -348,11 +490,19 @@ static int spi_nor_configure(struct device *dev)
 	data->spi_cfg.cs = &data->cs_ctrl;
 #endif /* DT_INST_0_JEDEC_SPI_NOR_CS_GPIOS_CONTROLLER */
 
+	/* Might be in DPD if system restarted without power cycle. */
+	exit_dpd(dev);
+
 	/* now the spi bus is configured, we can verify the flash id */
 	if (spi_nor_read_id(dev, params) != 0) {
 		return -ENODEV;
 	}
 
+	if (IS_ENABLED(CONFIG_SPI_NOR_IDLE_IN_DPD)
+	    && (enter_dpd(dev) != 0)) {
+		return -ENODEV;
+	}
+
 	return 0;
 }
 

drivers/flash/spi_nor.h

@@ -39,6 +39,8 @@ struct spi_nor_config {
 #define SPI_NOR_CMD_CE          0xC7    /* Chip erase */
 #define SPI_NOR_CMD_RDID        0x9F    /* Read JEDEC ID */
 #define SPI_NOR_CMD_ULBPR       0x98    /* Global Block Protection Unlock */
+#define SPI_NOR_CMD_DPD         0xB9    /* Deep Power Down */
+#define SPI_NOR_CMD_RDPD        0xAB    /* Release from Deep Power Down */
 
 /* Page, sector, and block size are standard, not configurable. */
 #define SPI_NOR_PAGE_SIZE    0x0100U

samples/drivers/spi_flash/sample.yaml

@@ -16,3 +16,10 @@ tests:
             - "Data read 55 aa"
             - "Data read matches with data written. Good!!"
     depends_on: spi
+  sample.driver.spi_flash_dpd:
+    tags: spi flash
+    filter: dt_compat_enabled("jedec,spi-nor")
+    build_only: true
+    extra_configs:
+      - CONFIG_SPI_NOR_IDLE_IN_DPD=y
+    depends_on: spi