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 on bus, hardware will gate off the card clock. But in
some case, we need the card clock keep on. Take IO voltage 1.8v switch
as example, after IO voltage change to 1.8v, spec require gate off the
card clock for 5ms, and gate on the clock back, once detect the card
clock on, then the card will draw the dat0 to high immediately. If there
is not clock gate off/on behavior, some card will keep the dat0 to low
level. This is the reason we fail in mmc_switch_voltage().

To fix this issue, and concern that this is only the fsl usdhc hardware
design limitation, set the bit FRC_SDCLK_ON in the beginning of the
wait_dat0() and clear it in the end. To make sure the 1.8v IO voltage
switch process align with SD specification.

For standard tuning process, usdhc specification also require the card
clock keep on, so also add these behavior in fsl_esdhc_execute_tuning().

Reviewed-by: Marek Vasut <marex@denx.de>
Tested-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Haibo Chen <haibo.chen@nxp.com>
Reviewed-by: Peng Fan <peng.fan@nxp.com>
Reviewed-by: Jaehoon Chung <jh80.chung@samsung.com>