Tab after int?

What units is freq in?

In Hz, the value passed is the clock one in struct mmc_ios

This should be under #if defined(SOC_ALLWINNER_A10) || ...

You should add a default case above to set clk to an invalid value to get into here.

Set error in the default case.

You don't need bst or bsh, you can use bus_read_4((sc)->res, ...) and bus_write_4((sc)->res, ...)

How long are these lines?

Only needed on A10?

As this value is returned it should be positive and code from errno, maybe ENXIO.

Put the >> at the end of the line. The convention is "... put the operator at the end of the line."

Missing software reset here (AHB1_RST_REG0). Shouldn't rely on U-Boot to set this up for us as the power on default for all of these peripherals is to have the reset line asserted.

Missing software reset (APB2_RST_REG)

Are these used anywhere?

When modifying a PLL on A31, there is a lock status bit in PLL<n>_CFG_REG. It will read back as 1 when the PLL becomes stable. You should wait for this bit to set before returning whenever you make a change.

I think you need to set A31_CCM_AHB1_RST_REG0_GMAC here, not clear it. 0 is reset asserted, 1 is reset de-asserted.

magic number

#define<tab>

I don't think so, I blindly ported the a10 clk driver as a base.

And it's not even needed, a31 doesn't have TWI4 ...

In case the PLL doesn't lock, there should be a timeout here.

I think you want if (i == PLL6_TIMEOUT)