atmel-mci: Add experimental DMA support

This adds support for DMA transfers through the generic DMA engine
framework with the DMA slave extensions.

The driver has been tested using mmc-block and ext3fs on several SD,
SDHC and MMC+ cards. Reads and writes work fine, with read transfer
rates up to 7.5 MiB/s on fast cards with debugging disabled.

Unfortunately, the driver has been known to lock up from time to time
with DMA enabled, so DMA support is currently optional and marked
EXPERIMENTAL. However, I didn't see any problems while testing 13
different cards (MMC, SD and SDHC of different brands and sizes), so I
suspect the "Initialize BLKR before sending data transfer command" fix
that was posted earlier fixed this as well.

Signed-off-by: Haavard Skinnemoen <haavard.skinnemoen@atmel.com>

1 files changed, 11 insertions, 0 deletions

diff --git a/drivers/mmc/host/Kconfig b/drivers/mmc/host/Kconfig
index ea8d7a3490d9..1ce21d4c8608 100644
--- a/drivers/mmc/host/Kconfig
+++ b/drivers/mmc/host/Kconfig
@@ -114,6 +114,17 @@ config MMC_ATMELMCI
 
           If unsure, say N.
 
+config MMC_ATMELMCI_DMA
+        bool "Atmel MCI DMA support (EXPERIMENTAL)"
+        depends on MMC_ATMELMCI && DMA_ENGINE && EXPERIMENTAL
+        help
+          Say Y here to have the Atmel MCI driver use a DMA engine to
+          do data transfers and thus increase the throughput and
+          reduce the CPU utilization. Note that this is highly
+          experimental and may cause the driver to lock up.
+
+          If unsure, say N.
+
 config MMC_IMX
         tristate "Motorola i.MX Multimedia Card Interface support"
         depends on ARCH_IMX