[MTD] [NAND] subpage read feature as a way to increase performance.

This patch enables NAND subpage read functionality.
If upper layer drivers are requesting to read non page aligned data NAND
subpage-read functionality reads the only whose ECC regions which include
requested data when original code reads whole page.
This significantly improves performance in many cases.

Here are some digits :

UBI volume mount time
No subpage reads: 5.75 seconds
Subpage read patch: 2.42 seconds

Open/stat time for files on JFFS2 volume:
No subpage read  0m 5.36s
Subpage read     0m 2.88s

Signed-off-by Alexey Korolev <akorolev@infradead.org>
Acked-by: Artem Bityutskiy <dedekind@infradead.org>
Acked-by: Jörn Engel <joern@logfs.org>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/include/linux/mtd/nand.h b/include/linux/mtd/nand.h
index 863e22a0ddb..83f678702df 100644
--- a/include/linux/mtd/nand.h
+++ b/include/linux/mtd/nand.h
@@ -177,6 +177,7 @@ typedef enum {
 #define NAND_MUST_PAD(chip) (!(chip->options & NAND_NO_PADDING))
 #define NAND_HAS_CACHEPROG(chip) ((chip->options & NAND_CACHEPRG))
 #define NAND_HAS_COPYBACK(chip) ((chip->options & NAND_COPYBACK))
+#define NAND_SUBPAGE_READ(chip) ((chip->ecc.mode == NAND_ECC_SOFT))
 
 /* Mask to zero out the chip options, which come from the id table */
 #define NAND_CHIPOPTIONS_MSK	(0x0000ffff & ~NAND_NO_AUTOINCR)
@@ -274,6 +275,10 @@ struct nand_ecc_ctrl {
 	int			(*read_page)(struct mtd_info *mtd,
 					     struct nand_chip *chip,
 					     uint8_t *buf);
+	int			(*read_subpage)(struct mtd_info *mtd,
+					     struct nand_chip *chip,
+					     uint32_t offs, uint32_t len,
+					     uint8_t *buf);
 	void			(*write_page)(struct mtd_info *mtd,
 					      struct nand_chip *chip,
 					      const uint8_t *buf);