[U-Boot] [PATCH 1/4] Optimized nand_read_buf for kirkwood

[Phil Sutter]

The basic idea is taken from the linux-kernel, but further optimized.

First align the buffer to 8 bytes, then use ldrd/strd to read and store
in 8 byte quantities, then do the final bytes.

Tested using: 'date ; nand read.raw 0xE00000 0x0 0x10000 ; date'.
Without this patch, NAND read of 132MB took 49s (~2.69MB/s). With this
patch in place, reading the same amount of data was done in 27s
(~4.89MB/s). So read performance is increased by ~80%!

Signed-off-by: Nico Erfurth <ne at erfurth.eu>
Tested-by: Phil Sutter <phil.sutter at viprinet.com>
Cc: Prafulla Wadaskar <prafulla at marvell.com>
---
 drivers/mtd/nand/kirkwood_nand.c |   29 +++++++++++++++++++++++++++++
 1 files changed, 29 insertions(+), 0 deletions(-)

diff --git a/drivers/mtd/nand/kirkwood_nand.c b/drivers/mtd/nand/kirkwood_nand.c
index bdab5aa..e04a59f 100644
--- a/drivers/mtd/nand/kirkwood_nand.c
+++ b/drivers/mtd/nand/kirkwood_nand.c
@@ -38,6 +38,34 @@ struct kwnandf_registers {
 static struct kwnandf_registers *nf_reg =
 	(struct kwnandf_registers *)KW_NANDF_BASE;
 
+
+/* The basic idea is stolen from the linux kernel, but the inner loop is optimized a bit more */
+static void kw_nand_read_buf(struct mtd_info *mtd, uint8_t *buf, int len)
+{
+	struct nand_chip *chip = mtd->priv;
+
+	while (len && (unsigned long)buf & 7)
+	{
+		*buf++ = readb(chip->IO_ADDR_R);
+		len--;
+	};
+
+	asm volatile (
+		".LFlashLoop:\n"
+		"  subs\t%0, #8\n"
+		"  ldrpld\tr2, [%2]\n" // Read 2 words
+		"  strpld\tr2, [%1], #8\n" // Read 2 words
+		"  bpl\t.LFlashLoop\n" // This results in one additional loop if len%8 <> 0
+		"  addne\t%0, #8\n"
+		: "+&r" (len), "+&r" (buf)
+		: "r" (chip->IO_ADDR_R)
+		: "r2", "r3", "memory", "cc"
+	);
+
+	while (len--)
+		*buf++ = readb(chip->IO_ADDR_R);
+}
+
 /*
  * hardware specific access to control-lines/bits
  */
@@ -76,6 +104,7 @@ int board_nand_init(struct nand_chip *nand)
 	nand->options = NAND_COPYBACK | NAND_CACHEPRG | NAND_NO_PADDING;
 	nand->ecc.mode = NAND_ECC_SOFT;
 	nand->cmd_ctrl = kw_nand_hwcontrol;
+	nand->read_buf = kw_nand_read_buf;
 	nand->chip_delay = 40;
 	nand->select_chip = kw_nand_select_chip;
 	return 0;
-- 
1.7.3.4