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>

diff --git a/drivers/spi/atmel_spi.c b/drivers/spi/atmel_spi.c
index 7524a84bdd504212d03511a88e3284ed2f890ed6..01ad6320d96c627c103a738c20a451c5f33236aa 100644 (file)
--- 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)