spi: Provide common spi_message processing loop

The loops which SPI controller drivers use to process the list of transfers
in a spi_message are typically very similar and have some error prone areas
such as the handling of /CS. Help simplify drivers by factoring this code
out into the core - if drivers provide a transfer_one() function instead
of a transfer_one_message() function the core will handle processing at the
message level.

/CS can be controlled by either setting cs_gpio or providing a set_cs
function. If this is not possible for hardware reasons then both can be
omitted and the driver should continue to implement manual /CS handling.

This is a first step in refactoring and it is expected that there will be
further enhancements, for example factoring out of the mapping of transfers
for DMA and the initiation and completion of interrupt driven transfers.

Signed-off-by: Mark Brown <broonie@linaro.org>

1 files changed, 92 insertions, 0 deletions

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 8a30c6b..85c18d8 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -526,6 +526,95 @@ int spi_register_board_info(struct spi_board_info const *info, unsigned n)
 
 /*-------------------------------------------------------------------------*/
 
+static void spi_set_cs(struct spi_device *spi, bool enable)
+{
+	if (spi->mode & SPI_CS_HIGH)
+		enable = !enable;
+
+	if (spi->cs_gpio >= 0)
+		gpio_set_value(spi->cs_gpio, !enable);
+	else if (spi->master->set_cs)
+		spi->master->set_cs(spi, !enable);
+}
+
+/*
+ * spi_transfer_one_message - Default implementation of transfer_one_message()
+ *
+ * This is a standard implementation of transfer_one_message() for
+ * drivers which impelment a transfer_one() operation.  It provides
+ * standard handling of delays and chip select management.
+ */
+static int spi_transfer_one_message(struct spi_master *master,
+				    struct spi_message *msg)
+{
+	struct spi_transfer *xfer;
+	bool cur_cs = true;
+	bool keep_cs = false;
+	int ret = 0;
+
+	spi_set_cs(msg->spi, true);
+
+	list_for_each_entry(xfer, &msg->transfers, transfer_list) {
+		trace_spi_transfer_start(msg, xfer);
+
+		INIT_COMPLETION(master->xfer_completion);
+
+		ret = master->transfer_one(master, msg->spi, xfer);
+		if (ret < 0) {
+			dev_err(&msg->spi->dev,
+				"SPI transfer failed: %d\n", ret);
+			goto out;
+		}
+
+		if (ret > 0)
+			wait_for_completion(&master->xfer_completion);
+
+		trace_spi_transfer_stop(msg, xfer);
+
+		if (msg->status != -EINPROGRESS)
+			goto out;
+
+		if (xfer->delay_usecs)
+			udelay(xfer->delay_usecs);
+
+		if (xfer->cs_change) {
+			if (list_is_last(&xfer->transfer_list,
+					 &msg->transfers)) {
+				keep_cs = true;
+			} else {
+				cur_cs = !cur_cs;
+				spi_set_cs(msg->spi, cur_cs);
+			}
+		}
+
+		msg->actual_length += xfer->len;
+	}
+
+out:
+	if (ret != 0 || !keep_cs)
+		spi_set_cs(msg->spi, false);
+
+	if (msg->status == -EINPROGRESS)
+		msg->status = ret;
+
+	spi_finalize_current_message(master);
+
+	return ret;
+}
+
+/**
+ * spi_finalize_current_transfer - report completion of a transfer
+ *
+ * Called by SPI drivers using the core transfer_one_message()
+ * implementation to notify it that the current interrupt driven
+ * transfer has finised and the next one may be scheduled.
+ */
+void spi_finalize_current_transfer(struct spi_master *master)
+{
+	complete(&master->xfer_completion);
+}
+EXPORT_SYMBOL_GPL(spi_finalize_current_transfer);
+
 /**
  * spi_pump_messages - kthread work function which processes spi message queue
  * @work: pointer to kthread work struct contained in the master struct
@@ -836,6 +925,8 @@ static int spi_master_initialize_queue(struct spi_master *master)
 
 	master->queued = true;
 	master->transfer = spi_queued_transfer;
+	if (!master->transfer_one_message)
+		master->transfer_one_message = spi_transfer_one_message;
 
 	/* Initialize and start queue */
 	ret = spi_init_queue(master);
@@ -1242,6 +1333,7 @@ int spi_register_master(struct spi_master *master)
 	spin_lock_init(&master->bus_lock_spinlock);
 	mutex_init(&master->bus_lock_mutex);
 	master->bus_lock_flag = 0;
+	init_completion(&master->xfer_completion);
 
 	/* register the device, then userspace will see it.
 	 * registration fails if the bus ID is in use.