[PATCH 4/4] mtd: nand: nand_mxs: Add subpage read support

[Stefan Christ]

Hi Sascha,

On Tue, May 10, 2016 at 08:24:43AM +0200, Sascha Hauer wrote:
> subpage read support can significantly speed up scanning UBI volumes, so
> add support for it. This is inspired by the corresponding Kernel commit.
> Unlike in the kernel we add subpage read support for i.MX28 aswell.
> Testing it on i.MX28 revealed no problems.
> 
> Signed-off-by: Sascha Hauer <s.hauer at pengutronix.de>

Here is my 

    Tested-by: Stefan Christ <s.christ at phytec.de>

I measured the ubiattach time for two different NAND chips after an ubiformat
on the devices. It's around 30% faster. Here are the results:

    nand: NAND device: Manufacturer ID: 0x01, Chip ID: 0xd3
    (AMD/Spansion S34ML08G2), 1024MiB, page size: 2048, OOB size: 128

    # without patches
    barebox at Phytec phyFLEX-i.MX6 Quad Carrier-Board:/ time ubiattach  /dev/nand0.root
    UBI: scanning is finished
    UBI: registering /dev/nand0.root.ubi
    UBI: attached mtd0 (name "nand0.root", size 1010 MiB) to ubi0
    time: 9208ms

    # with patches
    barebox at Phytec phyFLEX-i.MX6 Quad Carrier-Board:/ time ubiattach  /dev/nand0.root
    time: 6524ms

    # Saved time 2684ms (-29%)
    

    nand: NAND device: Manufacturer ID: 0x2c, Chip ID: 0xdc
    (Micron MT29F4G08ABADAWP), 512MiB, page size: 2048, OOB size: 64

    # without patches 
    barebox at Phytec phyCORE-i.MX6 Duallite/SOLO with NAND:/ time ubiattach /dev/nand0.root
    time: 4158ms

    # with patches
    barebox at Phytec phyCORE-i.MX6 Duallite/SOLO with NAND:/ time ubiattach /dev/nand0.root
    time: 2842ms

    # Saved time 1316ms (-31%)

Mit freundlichen Grüßen / Kind regards,
	Stefan Christ