Haibo Chen authored Feb 22, 2022 and Jaehoon Chung committed Mar 16, 2022

After commit f132aab4 ("Revert "mmc: fsl_esdhc_imx: use
VENDORSPEC_FRC_SDCLK_ON to control card clock output""), it
involve issue in mmc_switch_voltage(), because of the special
design of usdhc.

For FSL_USDHC, it do not implement VENDORSPEC_CKEN/PEREN/HCKEN/IPGEN,
these are reserved bits(Though RM contain the definition of these bits,
but actually internal IC logic do not implement, already confirm with
IC team). Instead, use VENDORSPEC_FRC_SDCLK_ON to gate on/off the card
clock output. Here is the definition of this bit in RM:

[8] FRC_SDCLK_ON
Force CLK output active
Do not set this bit to 1 unless it is necessary. Also, make sure that
this bit is cleared when uSDHC’s clock is about to be changed (frequency
change, clock source change, or delay chain tuning).
0b - CLK active or inactive is fully controlled by the hardware.
1b - Force CLK active

In default, the FRC_SDCLK_ON is 0. This means, when there is no command
or data transfer o...