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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...
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