[U-Boot] [PATCH 1/2] mtd: vf610_nfc: remove caching of page in buffer

[Stefan Agner]

To improve performance we remember the current page in the buffer
and avoid reading it twice. This implicit page cache increases
complexity while does not increase performance in real world cases.
This patch removes that feature.
---
As discussed in the other patchset...
http://thread.gmane.org/gmane.comp.boot-loaders.u-boot/215802

...I did some performance measurements:

Time to "Starting kernel ..."
- without bad block scan & with UBIFS fastmap: 2.02s
- with bad block scan & with UBIFS fastmap: 3.99s
- without bad block scan & without UBIFS fastmap: 4.42s
- with bad block scan & without UBIFS fastmap: 6.38s

Without page cache (with this patch applied):
Time to "Starting kernel ..."
- without bad block scan & with UBIFS fastmap: 2.02s
- with bad block scan & with UBIFS fastmap: 4.01s
- without bad block scan & without UBIFS fastmap: 4.41s
- with bad block scan & without UBIFS fastmap: 6.39s

I then checked whether that reread occurs at least once with a
printf in the "Already read?" if. It looks like this access
pattern does not occure (anymore?) during a normal boot.

Hence I now vote to get rid of it too...

 drivers/mtd/nand/vf610_nfc.c | 11 +----------
 1 file changed, 1 insertion(+), 10 deletions(-)

diff --git a/drivers/mtd/nand/vf610_nfc.c b/drivers/mtd/nand/vf610_nfc.c
index d98dd28..fa0bb9d 100644
--- a/drivers/mtd/nand/vf610_nfc.c
+++ b/drivers/mtd/nand/vf610_nfc.c
@@ -147,7 +147,6 @@ struct vf610_nfc {
 	uint               column;
 	int                spareonly;
 	int		   page_sz;
-	int                page;
 	/* Status and ID are in alternate locations. */
 	int                alt_buf;
 #define ALT_BUF_ID   1
@@ -347,7 +346,6 @@ static void vf610_nfc_command(struct mtd_info *mtd, unsigned command,
 
 	switch (command) {
 	case NAND_CMD_PAGEPROG:
-		nfc->page = -1;
 		vf610_nfc_transfer_size(nfc->regs, nfc->page_sz);
 		vf610_nfc_send_commands(nfc->regs, NAND_CMD_SEQIN,
 					command, PROGRAM_PAGE_CMD_CODE);
@@ -367,10 +365,6 @@ static void vf610_nfc_command(struct mtd_info *mtd, unsigned command,
 	case NAND_CMD_SEQIN: /* Pre-read for partial writes. */
 	case NAND_CMD_READ0:
 		column = 0;
-		/* Already read? */
-		if (nfc->page == page)
-			return;
-		nfc->page = page;
 		vf610_nfc_transfer_size(nfc->regs, nfc->page_sz);
 		vf610_nfc_send_commands(nfc->regs, NAND_CMD_READ0,
 					NAND_CMD_READSTART, READ_PAGE_CMD_CODE);
@@ -378,7 +372,6 @@ static void vf610_nfc_command(struct mtd_info *mtd, unsigned command,
 		break;
 
 	case NAND_CMD_ERASE1:
-		nfc->page = -1;
 		vf610_nfc_transfer_size(nfc->regs, 0);
 		vf610_nfc_send_commands(nfc->regs, command,
 					NAND_CMD_ERASE2, ERASE_CMD_CODE);
@@ -532,10 +525,8 @@ static inline int vf610_nfc_correct_data(struct mtd_info *mtd, u_char *dat)
 	flip = count_written_bits(dat, nfc->chip.ecc.size, ecc_count);
 
 	/* ECC failed. */
-	if (flip > ecc_count) {
-		nfc->page = -1;
+	if (flip > ecc_count)
 		return -1;
-	}
 
 	/* Erased page. */
 	memset(dat, 0xff, nfc->chip.ecc.size);
-- 
2.3.3