ARM: 7215/1: mmc: mmci: Increase max_segs from 16 to 128

A significant increase (10-20%) in performance throughput for
USB mass storage is the reason for incrementing the value.
By some reason the USB driver allocates buffers which requires
a scattergather list to contain a lot more than 16 elements to
get optimal performance. This change sets the maximum elements
to 128.

Tests with large reads and large writes (100 MiB) show that the
throughput increase is significant for write (10% for this test)
but not for read. Tests are run on a Linux host with ext4 FS on
the gadget mass storage device. The sg-len still exceeds 16 for
the read tests but the performance gain is low or nothing.

Tested-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Per Forlin <per.forlin@stericsson.com>
Signed-off-by: Ulf Hansson <ulf.hansson@stericsson.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 1 insertions, 1 deletions

diff --git a/drivers/mmc/host/mmci.h b/drivers/mmc/host/mmci.h
index 79e4143ab9df..49f153e6ef7a 100644
--- a/drivers/mmc/host/mmci.h
+++ b/drivers/mmc/host/mmci.h
@@ -160,7 +160,7 @@
         (MCI_RXFIFOHALFFULLMASK | MCI_RXDATAAVLBLMASK | \
          MCI_TXFIFOHALFEMPTYMASK)
 
-#define NR_SG           16
+#define NR_SG           128
 
 struct clk;
 struct variant_data;