Tanmay Kathpalia 906ee6785b mmc: sd: Handle UHS-I voltage signaling without power cycle ...

Some boards have SD card connectors where the power rail cannot be switched
off by the driver. However there are various circumstances when a card
might be re-initialized, such as after system resume, warm re-boot, or
error handling. However, a UHS card will continue to use 1.8V signaling
unless it is power cycled.

If the card has not been power cycled, it may still be using 1.8V
signaling. According to the SD spec., the Bus Speed Mode (function group 1)
bits 2 to 4 are zero if the card is initialized at 3.3V signal level. Thus
they can be used to determine if the card has already switched to 1.8V
signaling. Detect that situation and try to initialize a UHS-I (1.8V)
transfer mode.

Signed-off-by: Tanmay Kathpalia <tanmay.kathpalia@altera.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>

2025-10-30 10:11:18 +08:00

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