With the series "regulator: implement basic reference counter" [1], keeping regulator enablement in balance become more important.
A quick power cycle of a LDO regulator during dw-mmc signal voltage change, see patch 1, has shown that SD-card does not always get recognized after the vqmmc-supply is re-enabled.
Patch 2 fix this issue by applying a similar 400us enable_time delay the linux driver use.
Patch 1 is marked as DO NOT MERGE because it may have unintended affects like this and should be considered together with the "regulator: implement basic reference counter" series.
[1] https://patchwork.ozlabs.org/project/uboot/list/?series=351536
Jonas Karlman (2): DO NOT MERGE: mmc: dw_mmc: Keep vqmmc-supply enable count in balance power: regulator: rk8xx: Add 500us delay after LDO regulator is enabled
drivers/mmc/dw_mmc.c | 4 ++++ drivers/power/regulator/rk8xx.c | 4 ++++ 2 files changed, 8 insertions(+)