mem-to-mem copy using dma ...

[Ha N. <han...@gm...>]

Hi all,

I have to read UDP packets from sk_buff to my module in kernel space and the
udp stack uses copy_to_user() to do my task. I'm wondering if using dma for
mem-to-mem copy can improve data transfer performance instead of using
copy_to_user()???

If yes, could someone gives me some hints to go with it. I'm currently
working on ST7109 and stlinux 2.6.17.14. I have tried the guide at
http://www.stlinux.com/docs/manual/distribution/fdma_legacy.php but not
succeeded, kernel crashed with the following error:

Unable to handle kernel NULL pointer dereference at virtual address 00000000

pc = 86cd56aa
*pde = 00000000
Oops: 0001 [#1]

Pid : 818, Comm: udhcpc
PC is at create_llu_list+0x86/0x8c
PC : 86cd56aa SP : 8f633d38 SR : 40008001 TEA : c0103a64 Not tainted
R0 : 00000000 R1 : 00000000 R2 : 8f633d80 R3 : 00000001
R4 : 8f633d80 R5 : 00000000 R6 : 00000000 R7 : 00000000
R8 : 00000001 R9 : 8f633d40 R10 : 00000030 R11 : 86d6616c
R12 : 0f516ae0 R13 : 86d6616c R14 : 8fbc6000
MACH: 00000000 MACL: 00000000 GBR : 295737e8 PR : 86cd696c

I would really appreciate any feedback! Thanks!

/ha