[MX25][MMC]: SDHC very slow (300-600 KB/s) on i.MX25 board

[Stefan Koch <stefan.koch10@gmail.com>]

Hi,

I have ported linux-3.7-rc4 to a board with i.MX257 CPU.
As distribution I use Debian squeeze.
Booting time (with Xorg and IceWM) is different with different SD-Cards.
Boot time with 2GB Standard micro SD-Card: over 2:30 minutes
Boot time with 4GB Class 10 micro SDHC: 1:40 minutes
Boot time with 8GB UHS-1 micro SDHC: 1:15 minutes
Boot time with NFS (Network without SD/SDHC): 40 seconds

Starting applications is faster with NFS as with SD/SDHC.
At SD/SDHC linux is system is waiting a lot of time.
Then CPU can not run at 100% usage, so system is not so fast as possible.

Tests with dd give ratings from a. e. 300 KB/s (this could be a Class 10 
card).

But there is a relationship with slower and faster SD/SDHC-cards:
A UHS card works faster than a class 10 card an so on.
And a Standard 2GB SD card is the slowest.
But the Standard 2GB SC card works with a card reader connected to an 
Notebook faster than the UHS-1 Card in the imx257 Target system with imx 
integrated SDHC controller.

How to solve this problem?
Is it a driver issue?

Thanks

Stefan Koch