[RFC] mmc: meson-gx-mmc: add delay during poweroff

[Anand Moon]

Hi Da,

On Sat, 28 Jun 2025 at 09:15, Da Xue <da at libre.computer> wrote:
>
> Regulators controlling the SD card power need some settling time for SD
> cards to fully reset from UHS modes. The regulator framework seems to
> ignore falling times set in the device tree causing a few boards with the
> same hardware implementation to hang on reboot because the SD card still
> had some voltage and did not reset properly to be initialized again.
>
> Add a delay sufficiently long for the voltage to drop so that the SD card
> can reset properly. Otherwise the reboot will hang at missing SD card
> especially with Samsung cards.
>
Although the driver defines reset identifiers such as
RESET_SD_EMMC_A, RESET_SD_EMMC_B, and RESET_SD_EMMC_C,
It does not implement proper reset controller functionality,
specifically lacking support
for reset_control_assert() and reset_control_deassert() operations.

Thanks
-Anand