mtd: atmel_nand: enable Nand Flash Controller (NFC) write via sram

This patch enable writing nand flash via NFC SRAM. It will minimize the CPU
overhead. The SRAM write only support ECC_NONE and ECC_HW with PMECC.

To enable this NFC write by SRAM feature, you can add a string in dts under
NFC driver node.

This driver has been tested on SAMA5D3X-EK with JFFS2, YAFFS2, UBIFS and
mtd-utils.

Here is part of mtd_speedtest (writing test) result, compare with non-NFC
writing, it reduces %65 cpu load with loss %12 speed.

- commands use to test:
  # insmod /mnt/mtd_speedtest.ko dev=2 &
  # top -n 30 -d 1 | grep speedtest

- test result:
=================================================
mtd_speedtest: MTD device: 2
mtd_speedtest: MTD device size 41943040, eraseblock size 131072, page size 2048, count of eraseblocks 320, pages per eraseblock 64, OOB size 64
mtd_speedtest: testing eraseblock write speed
  509   495 root     D     1164   0%   7% insmod /mnt/mtd_speedtest.ko dev=2
  509   495 root     D     1164   0%   8% insmod /mnt/mtd_speedtest.ko dev=2
  509   495 root     R     1164   0%   5% insmod /mnt/mtd_speedtest.ko dev=2
mtd_speedtest: eraseblock write speed is 5194 KiB/s
mtd_speedtest: testing page write speed
  509   495 root     D     1164   0%  32% insmod /mnt/mtd_speedtest.ko dev=2
  509   495 root     D     1164   0%  27% insmod /mnt/mtd_speedtest.ko dev=2
  509   495 root     D     1164   0%  25% insmod /mnt/mtd_speedtest.ko dev=2
  509   495 root     D     1164   0%  30% insmod /mnt/mtd_speedtest.ko dev=2
mtd_speedtest: page write speed is 5024 KiB/s

Signed-off-by: Josh Wu <josh.wu@atmel.com>
Acked-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/Documentation/devicetree/bindings/mtd/atmel-nand.txt b/Documentation/devicetree/bindings/mtd/atmel-nand.txt
index 5d8b7d5c914..c4728839d0c 100644
--- a/Documentation/devicetree/bindings/mtd/atmel-nand.txt
+++ b/Documentation/devicetree/bindings/mtd/atmel-nand.txt
@@ -36,6 +36,8 @@ Optional properties:
     - reg : should specify the address and size used for NFC command registers,
             NFC registers and NFC Sram. NFC Sram address and size can be absent
             if don't want to use it.
+  - Optional properties:
+    - atmel,write-by-sram: boolean to enable NFC write by sram.
 
 Examples:
 nand0: nand@40000000,0 {