[v2, 2/2] mmc: fsl_esdhc: workaround for hardware 3.3v IO reliability issue

[Peng Fan]

> Subject: [v2, 2/2] mmc: fsl_esdhc: workaround for hardware 3.3v IO reliability
> issue
> 
> When eSDHC operates at 3.3v, damage can accumulate in an internal level
> shifter at a higher than expected rate. The faster the interface runs, the more
> damage accumulates. This issue now is found on LX2160A
> eSDHC1 for only SD card.
> 
> The hardware workaround is recommended to use an on-board level shifter
> that is 1.8v on SoC side and 3.3v on SD card side.
> 
> For boards without hardware workaround, this option could be enabled,
> ensuring 1.8v IO voltage and disabling eSDHC if no card.
> This option assumes no hotplug, and u-boot has to make all the way to to
> linux to use 1.8v UHS-I speed mode if has card.
> If you do not want the workaround for better user experience, of course you
> can choose to not select it running eSDHC in unsafe mode.
> 
> Signed-off-by: Yangbo Lu <yangbo.lu at nxp.com>

Acked-by: Peng Fan <peng.fan at nxp.com>