[PATCH 1/4] spi: Add option to wake a device by toggling CS

[apronin@xxxxxxxxxxxx]

From: Andrey Pronin <apronin@xxxxxxxxxxxx>

Some SPI devices may go to sleep after a period of inactivity
on SPI. For such devices, if enough time has passed since the
last SPI transaction, toggle CS and wait for the device to
start before communicating with it.

Signed-off-by: Andrey Pronin <apronin@xxxxxxxxxxxx>
---
 drivers/spi/spi.c       | 65 +++++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/spi/spi.h | 17 +++++++++++++
 2 files changed, 82 insertions(+)

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 77e6e45..c51c864 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -700,6 +700,20 @@ static void spi_set_cs(struct spi_device *spi, bool enable)
 		spi->master->set_cs(spi, !enable);
 }
 
+static void spi_cs_wake_timer_func(unsigned long arg)
+{
+	struct spi_device *spi = (struct spi_device *)arg;
+
+	spi->cs_wake_needed = true;
+}
+
+static void spi_reset_cs_wake_timer(struct spi_device *spi)
+{
+	spi->cs_wake_needed = false;
+	mod_timer(&spi->cs_wake_timer,
+		  jiffies + spi->cs_sleep_jiffies);
+}
+
 #ifdef CONFIG_HAS_DMA
 static int spi_map_buf(struct spi_master *master, struct device *dev,
 		       struct sg_table *sgt, void *buf, size_t len,
@@ -948,6 +962,15 @@ static int spi_transfer_one_message(struct spi_master *master,
 	struct spi_statistics *statm = &master->statistics;
 	struct spi_statistics *stats = &msg->spi->statistics;
 
+	if (msg->spi->cs_wake_after_sleep && msg->spi->cs_wake_needed) {
+		dev_info(&msg->spi->dev, "waking after possible sleep\n");
+		spi_set_cs(msg->spi, true);
+		mdelay(1);
+		spi_set_cs(msg->spi, false);
+		msleep(msg->spi->cs_wake_duration);
+		spi_reset_cs_wake_timer(msg->spi);
+	}
+
 	spi_set_cs(msg->spi, true);
 
 	SPI_STATISTICS_INCREMENT_FIELD(statm, messages);
@@ -1024,6 +1047,9 @@ out:
 	if (ret != 0 || !keep_cs)
 		spi_set_cs(msg->spi, false);
 
+	if (msg->spi->cs_wake_after_sleep && !ret)
+		spi_reset_cs_wake_timer(msg->spi);
+
 	if (msg->status == -EINPROGRESS)
 		msg->status = ret;
 
@@ -1551,6 +1577,45 @@ of_register_spi_device(struct spi_master *master, struct device_node *nc)
 	}
 	spi->max_speed_hz = value;
 
+	/* Do we need to assert CS to wake the device after sleep */
+	spi->cs_wake_after_sleep =
+		of_property_read_bool(nc, "cs-wake-after-sleep");
+	if (spi->cs_wake_after_sleep) {
+		dev_info(&master->dev, "cs-wake-after-sleep enabled\n");
+
+		/* After what delay device goes to sleep */
+		rc = of_property_read_u32(nc, "cs-sleep-delay", &value);
+		if (rc) {
+			dev_err(&master->dev,
+				"%s has no valid 'cs-sleep-delay' property (%d)\n",
+				nc->full_name, rc);
+			goto err_out;
+		}
+		spi->cs_sleep_jiffies = value * HZ / 1000; /* jiffies */
+
+		/* How long to wait after waking */
+		rc = of_property_read_u32(nc, "cs-wake-duration", &value);
+		if (rc) {
+			dev_err(&master->dev,
+				"%s has no valid 'cs-wake-duration' property (%d)\n",
+				nc->full_name, rc);
+			goto err_out;
+		}
+		spi->cs_wake_duration = value; /* msec */
+
+		/* Wake before accessing for the 1st time */
+		spi->cs_wake_needed = true;
+		init_timer(&spi->cs_wake_timer);
+		spi->cs_wake_timer.data = (unsigned long)spi;
+		spi->cs_wake_timer.function = spi_cs_wake_timer_func;
+	}
+
+	/* Should there be a delay before each transfer */
+	spi->xfer_delay = 0;
+	of_property_read_u32(nc, "xfer-delay", &spi->xfer_delay);
+	if (spi->xfer_delay)
+		dev_info(&master->dev, "xfer-delay = %u\n", spi->xfer_delay);
+
 	/* Store a pointer to the node in the device structure */
 	of_node_get(nc);
 	spi->dev.of_node = nc;
diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index 1f03483..4b06ba6 100644
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -126,6 +126,17 @@ void spi_statistics_add_transfer_stats(struct spi_statistics *stats,
  * @cs_gpio: gpio number of the chipselect line (optional, -ENOENT when
  *	when not using a GPIO line)
  *
+ * @cs_wake_after_sleep: Briefly toggle CS before talking to a device
+ *	if it could go to sleep.
+ * @cs_sleep_jiffies: Delay after which a device may go to sleep if there
+ *	was no SPI activity for it (jiffies).
+ * @cs_wake_duration: Delay after waking the device by toggling CS before
+ *	it is ready (msec).
+ * @cs_wake_needed: Is the wake needed (cs_sleep_jiffies passed since
+ *	the last SPI transaction).
+ * @cs_wake_timer: Timer measuring the delay before the device goes to
+ *	sleep after the last SPI transaction.
+ *
  * @statistics: statistics for the spi_device
  *
  * A @spi_device is used to interchange data between an SPI slave
@@ -166,6 +177,12 @@ struct spi_device {
 	char			modalias[SPI_NAME_SIZE];
 	int			cs_gpio;	/* chip select gpio */
 
+	bool			cs_wake_after_sleep;
+	unsigned long		cs_sleep_jiffies;
+	unsigned long		cs_wake_duration;
+	bool			cs_wake_needed;
+	struct timer_list	cs_wake_timer;
+
 	/* the statistics */
 	struct spi_statistics	statistics;
 
-- 
2.6.6

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