try workqueue for efficiency

ads1278_core.c

@@ -2,6 +2,7 @@
 #include <linux/dma-mapping.h>
 #include <linux/kernel.h>
 #include <linux/module.h>
+#include <linux/workqueue.h>
 #include <linux/spi/spi.h>
 
 #define FRAME_SIZE	(24)
@@ -11,14 +12,15 @@
 // 10'000'000 Hz =  52 kSPS
 #define TRANSFER_HZ	(27000000)
 
-// TODO:
-// - Require max CPU clock speed so 130 kSPS can be achieved
-// - Minimize ~30us delay between transfers
-// - Figure out how to get sample data out
-// - Create configuration interface
+// TODO: minimize 45us delay between xfers
+
+// 24-11-23: We're hitting 130 kSPS initially, but are eventually slowed down
+// to 87 kSPS. Need to investigate high-priority workers, forcing a high SPI
+// clock speed, and/or minimizing overall latency.
 
 struct ads1278
 {
+	struct workqueue_struct *wq;
 	unsigned char *rx;
 	unsigned char *tx;
 	dma_addr_t rx_dma_handle;
@@ -29,26 +31,43 @@ struct ads1278
 	int running[2];
 };
 
-static void ads1278_transfer_callback1(void *context)
+static struct spi_device *spip = NULL;
+static void ads1278_work_handler(struct work_struct *w)
 {
-	struct spi_device *spi = (struct spi_device *)context;
-        struct ads1278 *ads = spi_get_drvdata(spi);
+	struct ads1278 *ads;
+
+	if (!spip)
+		return;
+
+        ads = spi_get_drvdata(spip);
 
-	if (!ads->stop_requested)
-		spi_async(spi, &ads->msg[0]);
-	else
-		ads->running[0] = 0;
+	while (!ads->stop_requested) {
+		spi_sync_locked(spip, &ads->msg[0]);
+	}
 }
+static DECLARE_WORK(ads1278_work, ads1278_work_handler);
 
-static void ads1278_transfer_callback2(void *context)
+static void ads1278_transfer_callback1(void *context)
 {
-	struct spi_device *spi = (struct spi_device *)context;
-        struct ads1278 *ads = spi_get_drvdata(spi);
+//	struct spi_device *spi = (struct spi_device *)context;
+//        struct ads1278 *ads = spi_get_drvdata(spi);
+//
+//	if (!ads->stop_requested)
+//		queue_work(ads->wq, &ads1278_work);
+//		//spi_async(spi, &ads->msg[0]);
+//	else
+//		ads->running[0] = 0;
+}
 
-	if (!ads->stop_requested)
-		spi_async(spi, &ads->msg[1]);
-	else
-		ads->running[1] = 0;
+static void ads1278_transfer_callback2(void *context)
+{
+//	struct spi_device *spi = (struct spi_device *)context;
+//        struct ads1278 *ads = spi_get_drvdata(spi);
+//
+//	if (!ads->stop_requested)
+//		spi_async(spi, &ads->msg[1]);
+//	else
+//		ads->running[1] = 0;
 }
 
 
@@ -119,8 +138,16 @@ static int ads1278_begin_transfer(struct spi_device *spi)
 	ads->running[0] = 1;
 	ads->running[1] = 1;
 
-	/* TODO ret = */ spi_async(spi, &ads->msg[0]);
-	return spi_async(spi, &ads->msg[1]);
+//	/* TODO ret = */ spi_async(spi, &ads->msg[0]);
+//	return spi_async(spi, &ads->msg[1]);
+
+	ads->wq = create_singlethread_workqueue("ads1278");
+	if (ads->wq) {
+		spip = spi;
+		queue_work(ads->wq, &ads1278_work);
+	}
+
+	return 0;
 }
 
 static int ads1278_probe(struct spi_device *spi)
@@ -149,6 +176,7 @@ static int ads1278_probe(struct spi_device *spi)
 
 	dev_info(&spi->dev, "ready to go!");
 
+	spi_bus_lock(spi->controller);
 	if (ads1278_begin_transfer(spi)) {
 		dev_err(&spi->dev, "error with initial transfer!");
 		goto end_free_ads;
@@ -184,9 +212,14 @@ static void ads1278_remove(struct spi_device *spi)
 		dma_free_coherent(&spi->dev, TRANSFER_SIZE * 2, ads->tx, ads->tx_dma_handle);
 		dma_free_coherent(&spi->dev, TRANSFER_SIZE * 2, ads->rx, ads->rx_dma_handle);
 
+		flush_scheduled_work();
+		if (ads->wq)
+			destroy_workqueue(ads->wq);
+
 		kfree(ads);
 	}
 
+	spi_bus_unlock(spi->controller);
 	dev_info(&spi->dev, "done.");
 }