1 files changed, 43 insertions, 14 deletions

diff --git a/drivers/spi/pxa2xx_spi.c b/drivers/spi/pxa2xx_spi.c
index a7b9070e1b46..0e53354c1cfe 100644
--- a/drivers/spi/pxa2xx_spi.c
+++ b/drivers/spi/pxa2xx_spi.c
@@ -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 data)
                         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 data)
                                                         &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 data)
 
         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;