spi: omap2_mcspi rxdma bugfix

When data is read through DMA, the last element must be read separately
through the RX register.  It cannot be transferred by the DMA.  For
further details see e.g.  OMAP35x TRM (table 19-16).

Without the fix the driver causes extra clocks to be clocked to the bus
after DMA RX operations.  This can cause interesting behaviour with some
devices.

Signed-off-by: Juuso Oikarinen <juuso.oikarinen@nokia.com>
Signed-off-by: Eero Nurkkala <ext-eero.nurkkala@nokia.com>
[aaro.koskinen@nokia.com: Simplified the patch while keeping the idea.]
Signed-off-by: Aaro Koskinen <aaro.koskinen@nokia.com>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/drivers/spi/omap2_mcspi.c b/drivers/spi/omap2_mcspi.c
index 2b64091b0f1f31b41206311830df5773df05b32a..9b80ad36dbbad224c28d89475d0f91e8794d826b 100644 (file)
--- a/drivers/spi/omap2_mcspi.c
+++ b/drivers/spi/omap2_mcspi.c
@@ -272,7 +272,7 @@ omap2_mcspi_txrx_dma(struct spi_device *spi, struct spi_transfer *xfer)
 
        if (rx != NULL) {
                omap_set_dma_transfer_params(mcspi_dma->dma_rx_channel,
-                               data_type, element_count, 1,
+                               data_type, element_count - 1, 1,
                                OMAP_DMA_SYNC_ELEMENT,
                                mcspi_dma->dma_rx_sync_dev, 1);
 
@@ -303,6 +303,25 @@ omap2_mcspi_txrx_dma(struct spi_device *spi, struct spi_transfer *xfer)
        if (rx != NULL) {
                wait_for_completion(&mcspi_dma->dma_rx_completion);
                dma_unmap_single(NULL, xfer->rx_dma, count, DMA_FROM_DEVICE);
+               omap2_mcspi_set_enable(spi, 0);
+               if (likely(mcspi_read_cs_reg(spi, OMAP2_MCSPI_CHSTAT0)
+                               & OMAP2_MCSPI_CHSTAT_RXS)) {
+                       u32 w;
+
+                       w = mcspi_read_cs_reg(spi, OMAP2_MCSPI_RX0);
+                       if (word_len <= 8)
+                               ((u8 *)xfer->rx_buf)[element_count - 1] = w;
+                       else if (word_len <= 16)
+                               ((u16 *)xfer->rx_buf)[element_count - 1] = w;
+                       else /* word_len <= 32 */
+                               ((u32 *)xfer->rx_buf)[element_count - 1] = w;
+               } else {
+                       dev_err(&spi->dev, "DMA RX last word empty");
+                       count -= (word_len <= 8)  ? 1 :
+                                (word_len <= 16) ? 2 :
+                              /* word_len <= 32 */ 4;
+               }
+               omap2_mcspi_set_enable(spi, 1);
        }
        return count;
 }