pxa2xx_spi: dma bugfixes

@@ -47,9 +47,10 @@ MODULE_ALIAS("platform:pxa2xx-spi");
 
 #define MAX_BUSES 3
 
-#define DMA_INT_MASK (DCSR_ENDINTR | DCSR_STARTINTR | DCSR_BUSERR)
-#define RESET_DMA_CHANNEL (DCSR_NODESC | DMA_INT_MASK)
-#define IS_DMA_ALIGNED(x) (((u32)(x)&0x07)==0)
+#define DMA_INT_MASK		(DCSR_ENDINTR | DCSR_STARTINTR | DCSR_BUSERR)
+#define RESET_DMA_CHANNEL	(DCSR_NODESC | DMA_INT_MASK)
+#define IS_DMA_ALIGNED(x)	(((x) & 0x07) == 0)
+#define MAX_DMA_LEN		8191
 
 /*
  * for testing SSCR1 changes that require SSP restart, basically

@@ -887,14 +888,27 @@ static void pump_transfers(unsigned long
 			drv_data->cs_control(PXA2XX_CS_DEASSERT);
 	}
 
-	/* Check transfer length */
-	if (transfer->len > 8191)
-	{
-		dev_warn(&drv_data->pdev->dev, "pump_transfers: transfer "
-				"length greater than 8191\n");
-		message->status = -EINVAL;
-		giveback(drv_data);
-		return;
+	/* Check for transfers that need multiple DMA segments */
+	if (transfer->len > MAX_DMA_LEN && chip->enable_dma) {
+
+		/* reject already-mapped transfers; PIO won't always work */
+		if (message->is_dma_mapped
+				|| transfer->rx_dma || transfer->tx_dma) {
+			dev_err(&drv_data->pdev->dev,
+				"pump_transfers: mapped transfer length "
+				"of %lu is greater than %d\n",
+				transfer->len, MAX_DMA_LEN);
+			message->status = -EINVAL;
+			giveback(drv_data);
+			return;
+		}
+
+		/* warn ... we force this to PIO mode */
+		if (printk_ratelimit())
+			dev_warn(&message->spi->dev, "pump_transfers: "
+				"DMA disabled for transfer length %ld "
+				"greater than %d\n",
+				(long)drv_data->len, MAX_DMA_LEN);
 	}
 
 	/* Setup the transfer state based on the type of transfer */

@@ -962,7 +976,7 @@ static void pump_transfers(unsigned long
 							&dma_thresh))
 				if (printk_ratelimit())
 					dev_warn(&message->spi->dev,
-						"pump_transfer: "
+						"pump_transfers: "
 						"DMA burst size reduced to "
 						"match bits_per_word\n");
 		}

@@ -976,8 +990,23 @@ static void pump_transfers(unsigned long
 
 	message->state = RUNNING_STATE;
 
-	/* Try to map dma buffer and do a dma transfer if successful */
-	if ((drv_data->dma_mapped = map_dma_buffers(drv_data))) {
+	/* Try to map dma buffer and do a dma transfer if successful, but
+	 * only if the length is non-zero and less than MAX_DMA_LEN.
+	 *
+	 * Zero-length non-descriptor DMA is illegal on PXA2xx; force use
+	 * of PIO instead.  Care is needed above because the transfer may
+	 * have have been passed with buffers that are already dma mapped.
+	 * A zero-length transfer in PIO mode will not try to write/read
+	 * to/from the buffers
+	 *
+	 * REVISIT large transfers are exactly where we most want to be
+	 * using DMA.  If this happens much, split those transfers into
+	 * multiple DMA segments rather than forcing PIO.
+	 */
+	drv_data->dma_mapped = 0;
+	if (drv_data->len > 0 && drv_data->len <= MAX_DMA_LEN)
+		drv_data->dma_mapped = map_dma_buffers(drv_data);
+	if (drv_data->dma_mapped) {
 
 		/* Ensure we have the correct interrupt handler */
 		drv_data->transfer_handler = dma_transfer;