During reset the VMMC regulator doesn't reach 0V and only drops to
1.8V, furthermore the pulse width is under 200us whereas the SD
specification expect 1ms.

The WR_S bit allows the TWL6030 to no reset at all the VMMC during warm
reset and keep the current voltage. Thanks to this workaround the SD
card doesn't reach a undefined reset stage.

Actually this behavior is available for all the LDO regulator, so the
driver will also allow to use it with any of these regulator.
Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>
Link: https://lore.kernel.org/r/20190725094542.16547-4-gregory.clement@bootlin.comSigned-off-by: Mark Brown <broonie@kernel.org>