My previous article will some help for spidev configuration on iMX28EVK Linux.
SPI: SPIDEV interface question
Note that iMX28 SPI base clock is fixed to 120MHz and SPI clock is 1/n (n >= 2) of the base clock.
If this is inconvenient, you may try to change base clock at drivers/spi/spi_mxs.c at
static int __init mxs_spi_probe(struct platform_device *dev)
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clk_set_rate(ss->clk, 120 * 1000 * 1000)
For spidev usage, there is good description in Linux Kernel document linux-2.6.35.3/Documentation/spi/.