spi: Add an helper to flush the message queue

This is needed by the spi-mem logic to force all messages that have been
queued before a memory operation to be sent before we start the memory
operation. We do that in order to guarantee that spi-mem operations do
not preempt regular SPI transfers.

Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/internals.h

@@ -17,6 +17,8 @@
 #include <linux/scatterlist.h>
 #include <linux/spi/spi.h>
 
+void spi_flush_queue(struct spi_controller *ctrl);
+
 #ifdef CONFIG_HAS_DMA
 int spi_map_buf(struct spi_controller *ctlr, struct device *dev,
 		struct sg_table *sgt, void *buf, size_t len,

drivers/spi/spi.c

@@ -1522,6 +1522,22 @@ err_init_queue:
 	return ret;
 }
 
+/**
+ * spi_flush_queue - Send all pending messages in the queue from the callers'
+ *		     context
+ * @ctlr: controller to process queue for
+ *
+ * This should be used when one wants to ensure all pending messages have been
+ * sent before doing something. Is used by the spi-mem code to make sure SPI
+ * memory operations do not preempt regular SPI transfers that have been queued
+ * before the spi-mem operation.
+ */
+void spi_flush_queue(struct spi_controller *ctlr)
+{
+	if (ctlr->transfer == spi_queued_transfer)
+		__spi_pump_messages(ctlr, false);
+}
+
 /*-------------------------------------------------------------------------*/
 
 #if defined(CONFIG_OF)