mtd: docg3: add fast mode

Docg3 chips can work in 3 modes : normal MLC mode, fast
mode and reliable mode. Normally, as docg3 is a MLC chip, it
should be configured to work in normal mode.

In both normal mode, each page is distinct. This
means that writing to page 12 of blocks 14,15 writes only to
that page, and reading from page 12 of blocks 14,15 reads
only from that page.

In reliable and fast modes, pages are coupled by pairs, and
are clones one of each other. This means that the available
capacity of the chip is halved. Pages are coupled in each
block, and page of index 2*n contains the same data as page
2*n+1 of the same block.

In fast mode, the reads occur a bit faster, but are a bit
less reliable that in normal mode.

When reading from page 2*n, the chip reads bytes from both
page 2*n and page 2*n+1, makes a logical and for each byte,
and returns the result. As programming a page means
"clearing bits", even if a bit was not cleared on one page
because the flash is worn out, the other page has the bit
cleared, and the result of the "AND" gives a correct result.

When writing to page 2*n, the chip writes data to both page
2*n and page 2*n+1.

Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Reviewed-by: Ivan Djelic <ivan.djelic@parrot.com>
Reviewed-by: Mike Dunn <mikedunn@newsguy.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

1 files changed, 8 insertions, 1 deletions

diff --git a/drivers/mtd/devices/docg3.h b/drivers/mtd/devices/docg3.h
index cd70b181f797..07182f9d484d 100644
--- a/drivers/mtd/devices/docg3.h
+++ b/drivers/mtd/devices/docg3.h
@@ -135,7 +135,8 @@
  */
 #define DOC_SEQ_RESET			0x00
 #define DOC_SEQ_PAGE_SIZE_532		0x03
-#define DOC_SEQ_SET_MODE		0x09
+#define DOC_SEQ_SET_FASTMODE		0x05
+#define DOC_SEQ_SET_RELIABLEMODE	0x09
 #define DOC_SEQ_READ			0x12
 #define DOC_SEQ_SET_PLANE1		0x0e
 #define DOC_SEQ_SET_PLANE2		0x10
@@ -257,6 +258,11 @@
  * @base: mapped IO space
  * @device_id: number of the cascaded DoCG3 device (0, 1, 2 or 3)
  * @if_cfg: if true, reads are on 16bits, else reads are on 8bits
+
+ * @reliable: if 0, docg3 in normal mode, if 1 docg3 in fast mode, if 2 in
+ *            reliable mode
+ *            Fast mode implies more errors than normal mode.
+ *            Reliable mode implies that page 2*n and 2*n+1 are clones.
  * @bbt: bad block table cache
  * @oob_write_ofs: offset of the MTD where this OOB should belong (ie. in next
  *                 page_write)
@@ -270,6 +276,7 @@ struct docg3 {
 	void __iomem *base;
 	unsigned int device_id:4;
 	unsigned int if_cfg:1;
+	unsigned int reliable:2;
 	int max_block;
 	u8 *bbt;
 	loff_t oob_write_ofs;