atmel_spi: minor updates

Minor updates to atmel_spi:

 - DMA:
    * Comments to explain the DMA policies
    * Report any mapping errors from spi_transfer()
    * Remove extra loop for DMA mapping

 - Diagnostics:  report minimum clock rate, if we need to reject a
   spi_setup() request because that rate is too low.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Acked-by: Haavard Skinnemoen <hskinnemoen@atmel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 45 insertions, 12 deletions

diff --git a/drivers/spi/atmel_spi.c b/drivers/spi/atmel_spi.c
index 7524a84bdd50..01ad6320d96c 100644
--- a/drivers/spi/atmel_spi.c
+++ b/drivers/spi/atmel_spi.c
@@ -184,18 +184,39 @@ static void atmel_spi_next_message(struct spi_master *master)
         atmel_spi_next_xfer(master, msg);
 }
 
-static void
+/*
+ * For DMA, tx_buf/tx_dma have the same relationship as rx_buf/rx_dma:
+ *  - The buffer is either valid for CPU access, else NULL
+ *  - If the buffer is valid, so is its DMA addresss
+ *
+ * This driver manages the dma addresss unless message->is_dma_mapped.
+ */
+static int
 atmel_spi_dma_map_xfer(struct atmel_spi *as, struct spi_transfer *xfer)
 {
+        struct device   *dev = &as->pdev->dev;
+
         xfer->tx_dma = xfer->rx_dma = INVALID_DMA_ADDRESS;
-        if (xfer->tx_buf)
-                xfer->tx_dma = dma_map_single(&as->pdev->dev,
+        if (xfer->tx_buf) {
+                xfer->tx_dma = dma_map_single(dev,
                                 (void *) xfer->tx_buf, xfer->len,
                                 DMA_TO_DEVICE);
-        if (xfer->rx_buf)
-                xfer->rx_dma = dma_map_single(&as->pdev->dev,
+                if (dma_mapping_error(xfer->tx_dma))
+                        return -ENOMEM;
+        }
+        if (xfer->rx_buf) {
+                xfer->rx_dma = dma_map_single(dev,
                                 xfer->rx_buf, xfer->len,
                                 DMA_FROM_DEVICE);
+                if (dma_mapping_error(xfer->tx_dma)) {
+                        if (xfer->tx_buf)
+                                dma_unmap_single(dev,
+                                                xfer->tx_dma, xfer->len,
+                                                DMA_TO_DEVICE);
+                        return -ENOMEM;
+                }
+        }
+        return 0;
 }
 
 static void atmel_spi_dma_unmap_xfer(struct spi_master *master,
@@ -398,8 +419,9 @@ static int atmel_spi_setup(struct spi_device *spi)
                 scbr = ((bus_hz + spi->max_speed_hz - 1)
                         / spi->max_speed_hz);
                 if (scbr >= (1 << SPI_SCBR_SIZE)) {
-                        dev_dbg(&spi->dev, "setup: %d Hz too slow, scbr %u\n",
-                                        spi->max_speed_hz, scbr);
+                        dev_dbg(&spi->dev,
+                                "setup: %d Hz too slow, scbr %u; min %ld Hz\n",
+                                spi->max_speed_hz, scbr, bus_hz/255);
                         return -EINVAL;
                 }
         } else
@@ -465,12 +487,19 @@ static int atmel_spi_transfer(struct spi_device *spi, struct spi_message *msg)
                         dev_dbg(&spi->dev, "no protocol options yet\n");
                         return -ENOPROTOOPT;
                 }
-        }
 
-        /* scrub dcache "early" */
-        if (!msg->is_dma_mapped) {
-                list_for_each_entry(xfer, &msg->transfers, transfer_list)
-                        atmel_spi_dma_map_xfer(as, xfer);
+                /*
+                 * DMA map early, for performance (empties dcache ASAP) and
+                 * better fault reporting.  This is a DMA-only driver.
+                 *
+                 * NOTE that if dma_unmap_single() ever starts to do work on
+                 * platforms supported by this driver, we would need to clean
+                 * up mappings for previously-mapped transfers.
+                 */
+                if (!msg->is_dma_mapped) {
+                        if (atmel_spi_dma_map_xfer(as, xfer) < 0)
+                                return -ENOMEM;
+                }
         }
 
         list_for_each_entry(xfer, &msg->transfers, transfer_list) {
@@ -537,6 +566,10 @@ static int __init atmel_spi_probe(struct platform_device *pdev)
 
         as = spi_master_get_devdata(master);
 
+        /*
+         * Scratch buffer is used for throwaway rx and tx data.
+         * It's coherent to minimize dcache pollution.
+         */
         as->buffer = dma_alloc_coherent(&pdev->dev, BUFFER_SIZE,
                                         &as->buffer_dma, GFP_KERNEL);
         if (!as->buffer)