It is not possible to put the card into transfer mode.
card_enter_trans in usdhc.c CMD7 send fails.
card_cmd_config(&cmd, CMD7, card_address, READ, (1<<0)|(1<<2)|(1<<4),//RESPONSE_48_CHECK_BUSY,
DATA_PRESENT_NONE, TRUE, TRUE);
If I ignore this, I can use card_data_read and card_data_write. Written data are saved, to weherever. Even after power down the data is still there, but whatever offset I choose, I get the same data.
It is a 4GB Toshiba eMMC chip on a Toradex Apalis board. Program is loaded over the serial bootloader, DCD and IVT from u-boot. Serial, GPIO and SPI works fine.