I upgrade my TL-WR741ND with Winbond W25Q64 8Mbyte FLASH chip.
First of all I made a full backup from the original (en25f32) with Topmax EEtols2.
Then I wrote this binary to the new flash because the bootloader (U-boot).
Then I made some modification in kernel (below) :
     - change the place and size of partitions
     - w25q64 JEDEC signature
After that I programmed the new chip via tftp method but there was a problem:

          U-Boot 1.1.4 (Mar  8 2010 - 10:29:42)

          AP91 (ar7240) U-boot
          DRAM: 
          sri
          #### TAP VALUE 1 = c, 2 = d
          64 MB
          id read 0x100000ff
          flash size 4194304, sector count = 64
          Flash:  4 MB
          Using default environment

          BOARD IS NOT CALIBRATED!!!

Yes, I forgot the "art" partition , the place of calibration data has changed...
So I had to copy 0x010000 bytes from original flash(0x3f0000) to new flash (0x7f0000).
After that the wifi interface worked well!

The first patches:

          --- a/arch/mips/ar71xx/mach-tl-wr741nd.c   
          +++ b/arch/mips/ar71xx/mach-tl-wr741nd.c   
          @@ -44,16 +44,16 @@
               } , {
                   .name        = "rootfs",
                   .offset        = 0x160000,
          -        .size        = 0x290000,
          +        .size        = 0x690000,
               } , {
                   .name        = "art",
          -        .offset        = 0x3f0000,
          +        .offset        = 0x7f0000,
                   .size        = 0x010000,
                   .mask_flags    = MTD_WRITEABLE,
               } , {
                   .name        = "firmware",
                   .offset        = 0x020000,
          -        .size        = 0x3d0000,
          +        .size        = 0x7d0000,
               }
           };
           #endif /* CONFIG_MTD_PARTITIONS */

and the other:

           --- a/drivers/mtd/devices/m25p80.c
           +++ b/drivers/mtd/devices/m25p80.c
           @@ -689,6 +689,7 @@ static struct flash_info __devinitdata m
                { "w25x80", 0xef3014, 0, 64 * 1024, 16, SECT_4K, },
                { "w25x16", 0xef3015, 0, 64 * 1024, 32, SECT_4K, },
                { "w25x32", 0xef3016, 0, 64 * 1024, 64, SECT_4K, },
           +    { "w25q64", 0xef4017, 0, 64 * 1024, 128, SECT_4K, },
                { "w25x64", 0xef3017, 0, 64 * 1024, 128, SECT_4K, },
            };

And the result of our work!

            root@OpenWrt:~# df

            Filesystem           1K-blocks      Used      Available      Use%     Mounted on
            /dev/root                 2176        2176           0            100%     /rom
            tmpfs                    31032           80           30952            0%   /tmp
            tmpfs                      512            0             512              0%    /dev
            root                      2176          2176            0            100%    /tmp/root
            mini_fo:/tmp/root     2176       2176            0            100%    /tmp/root
            /dev/mtdblock3        4612        244          4368            5%     /overlay
            mini_fo:/overlay      2176       2176            0           100%      /
   
If you want to programming the flash chips you can use Sergey's programmer but some changing needed because doesnt work with this chip.

Good luck for modifications!
If you have any question don't hesitate to ask!

Thanks.I'll try it on 841nd as soon as I get 8MB SPI flash ic.

Please do not have wifi ART.BIN for TL-WR841ND v7.2 (64K), or TL-MR3220
found that the key Mac and pin this on wifi and boot dd-wrt installed you can copy tothe folder / tmp/mtd7 fimware which is the entire rom with the command (dd if = /dev/mtd/7 of = / tmp / backup.bin) and then just copy to the pc via winscp ok, thank you Brazil,

I'm waiting for my new router tl-mr3220, if you can wait some days (and i dont forget it ) I will save&send to you the art.bin