• Philip Langdale's avatar
    MMC: Fix handling of low-voltage cards · 55556da0
    Philip Langdale authored
    Fix handling of low voltage MMC cards.
    
    The latest MMC and SD specs both agree that support for
    low-voltage operations is indicated by bit 7 in the OCR.
    The MMC spec states that the low voltage range is
    1.65-1.95V while the SD spec leaves the actual voltage
    range undefined - meaning that there is still no such
    thing as a low voltage SD card.
    
    However, an old Sandisk spec implied that bits 7.0
    represented voltages below 2.0V in 1V or 0.5V increments,
    and the code was accordingly written with that expectation.
    
    This confusion meant that host drivers attempting to support
    the typical low voltage (1.8V) would set the wrong bits in
    the host OCR mask (usually bits 5 and/or 6) resulting in the
    the low voltage mode never being used.
    
    This change corrects the low voltage range and adds sanity
    checks on the reserved bits (0-6) and for SD cards that
    claim to support low-voltage operations.
    Signed-off-by: default avatarPhilip Langdale <philipl@overt.org>
    Signed-off-by: default avatarPierre Ossman <drzeus@drzeus.cx>
    55556da0
sdhci.c 36.6 KB