[PATCH] mmc: dw_mmc: Fix the max_blk_count in IDMAC

[Yuvaraj Kumar C D]

From: Alim Akhtar <alim.akhtar at samsung.com>

max_blk_count is currently set incorrectly, and the correct value can
be determined by looking at the maximum number of bytes which can be
transferred and the block size.  We use the maximum block size to
determine the minimum number of blocks that the controller should
support.  It could probably do more with a smaller block size but this
value should be sufficient for good performance.

This improves sequential performance by 82% on write and 6% read on
one particular device.

TEST= with this patch
	time dd if=/dev/zero of=/usr/local/100 bs=1M count=100 conv=fdatasync
	100+0 records in
	100+0 records out
	104857600 bytes (105 MB) copied, 2.62541 s, 39.9 MB/s

	real    0m2.638s
	user    0m0.000s
	sys     0m0.645s

	without this patch:
	time dd if=/dev/zero of=/usr/local/100 bs=1M count=100 conv=fdatasync
	100+0 records in
	100+0 records out
	104857600 bytes (105 MB) copied, 3.25873 s, 32.2 MB/s

	real    0m3.265s
	user    0m0.005s
	sys     0m0.690s

Signed-off-by: Seungwon Jeon <tgih.jun at samsung.com>
Signed-off-by: Alim Akhtar <alim.akhtar at samsung.com>
Signed-off-by: Sonny Rao <sonnyrao at chromium.org>
Signed-off-by: Yuvaraj Kumar C D <yuvaraj.cd at samsung.com>
---
 drivers/mmc/host/dw_mmc.c |   18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
index 0c56faa..2fc4030 100644
--- a/drivers/mmc/host/dw_mmc.c
+++ b/drivers/mmc/host/dw_mmc.c
@@ -2213,10 +2213,24 @@ static int dw_mci_init_slot(struct dw_mci *host, unsigned int id)
 		/* Useful defaults if platform data is unset. */
 #ifdef CONFIG_MMC_DW_IDMAC
 		mmc->max_segs = host->ring_size;
+
+		/* the BLKSIZ register is 16-bits wide */
 		mmc->max_blk_size = 65536;
-		mmc->max_blk_count = host->ring_size;
+
+		/*
+		 * This value is calculated by taking the size of the
+		 * 32-bit BYTCNT (byte count) register and dividing by the
+		 * BLKSIZ (block size) register.  This is the minimum number
+		 * of blocks which could be handled.
+		 */
+		mmc->max_blk_count = 0xFFFF;
 		mmc->max_seg_size = 0x1000;
-		mmc->max_req_size = mmc->max_seg_size * mmc->max_blk_count;
+		/*
+		 * Maximum request size should be total number of descriptors
+		 * times the maximum amount of data each can reference
+		 */
+
+		mmc->max_req_size = mmc->max_seg_size * mmc->max_segs;
 #else
 		mmc->max_segs = 64;
 		mmc->max_blk_size = 65536; /* BLKSIZ is 16 bits */
-- 
1.7.10.4