mmc: support packed write command for eMMC4.5 devices

This patch supports packed write command of eMMC4.5 devices.  Several
writes can be grouped in packed command and all data of the individual
commands can be sent in a single transfer on the bus. Large amounts of
data in one transfer rather than several data of small size are
effective for eMMC write internally.  As a result, packed command help
write throughput be improved.  The following tables show the results
of packed write.

Type A:
test     none |  packed
iozone   25.8 |  31
tiotest  27.6 |  31.2
lmdd     31.2 |  35.4

Type B:
test     none |  packed
iozone   44.1 |  51.1
tiotest  47.9 |  52.5
lmdd     51.6 |  59.2

Type C:
test     none |  packed
iozone   19.5 |  32
tiotest  19.9 |  34.5
lmdd     22.8 |  40.7

Signed-off-by: Seungwon Jeon <tgih.jun@samsung.com>
Reviewed-by: Maya Erez <merez@codeaurora.org>
Reviewed-by: Namjae Jeon <linkinjeon@gmail.com>
Signed-off-by: Chris Ball <cjb@laptop.org>

1 files changed, 1 insertions, 0 deletions

diff --git a/drivers/mmc/core/mmc_ops.c b/drivers/mmc/core/mmc_ops.c
index 6d8f7012d73a..49f04bc9d0eb 100644
--- a/drivers/mmc/core/mmc_ops.c
+++ b/drivers/mmc/core/mmc_ops.c
@@ -363,6 +363,7 @@ int mmc_send_ext_csd(struct mmc_card *card, u8 *ext_csd)
         return mmc_send_cxd_data(card, card->host, MMC_SEND_EXT_CSD,
                         ext_csd, 512);
 }
+EXPORT_SYMBOL_GPL(mmc_send_ext_csd);
 
 int mmc_spi_read_ocr(struct mmc_host *host, int highcap, u32 *ocrp)
 {