Il 07/12/23 07:35, Axe Yang ha scritto:
Previously, during the MSDC calibration process, a full clock cycle actually not be covered, which in some cases didn't yield the best results and could cause CRC errors. This problem is particularly evident when MSDC is used as an SDIO host. In fact, MSDC support tuning up to a maximum of 64 steps, but by default, the step number is 32. By increase the tuning step, we are more likely to cover more parts of a clock cycle, and get better calibration result. To illustrate, when tuning 32 steps, if the obtained window has a hole near the middle, like this: 0xffc07ff (hex), then the selected delay will be the 6 (counting from right to left). (32 <- 1) 1111 1111 1100 0000 0000 0111 11(1)1 1111 However, if we tune 64 steps, the window obtained may look like this: 0xfffffffffffc07ff. The final selected delay will be 44, which is safer as it is further away from the hole: (64 <- 1) 1111 ... (1)111 1111 1111 1111 1111 1100 0000 0000 0111 1111 1111 In this case, delay 6 selected through 32 steps tuning is obviously not optimal, and this delay is closer to the hole, using it would easily cause CRC problems. As per mesaurements taken on mediatek SoC platform, the tuning phase will take: eMMC - 32 steps: ~3ms - 64 steps: ~6ms SDIO - 32 steps: ~4ms - 64 steos: ~7ms Tuning more steps won't prolong boot times by any meaningful amount of time, so for SD/SDIO the default tuning steps will be adjust to 64. But for eMMC, it is still preferred to use 32 steps tuning as otherwise there would be performance lose when accessing the RPMB partition(requiring retuning each time). You can configure property "mediatek,tuning-step" in MSDC dts node to adjust the step number. Signed-off-by: Axe Yang <axe.yang@xxxxxxxxxxxx>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@xxxxxxxxxxxxx>
