Hi Marek,
I built U-Boot 2012.04-rc1 and tried it with mx28evk. MMC seems to be broken. Reverting your commit 3687c4 (i.MX28: Do data transfers via DMA in MMC driver) fix the issue.
Also there is issue in setting MAC address. Console logs are at the end of this mail.
Best regards, Lauri Hintsala
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U-Boot 2012.04-rc1 (Apr 02 2012 - 17:19:53)
Freescale i.MX28 family at 454 MHz DRAM: 128 MiB MMC: MXS MMC: 0 MMC0: DMA transfer failed MMC0: DMA transfer failed MMC0: DMA transfer failed MMC0: DMA transfer failed MMC init failed Using default environment
In: serial Out: serial Err: serial Net: FEC0 Warning: failed to set MAC address , FEC1 Warning: failed to set MAC address
Hit any key to stop autoboot: 0 MX28EVK U-Boot > mmc rescan MMC0: DMA transfer failed MMC0: DMA transfer failed MMC0: DMA transfer failed MMC0: DMA transfer failed