I have been working with a DDR50 SD card that does not support tuning. The card's first tuning attempt fails, which is expected, but subsequent tuning attempts cause I/O errors due to async page reads. My first patch mostly solves this issue but I was still seeing I/O errors in the case where the card is reset and attempts to do the initial tuning again despite it failing previously. This second patch allows the initial tuning to be skipped if it has already failed for a DDR50 card.
