Messages in this thread | | | Date | Thu, 7 Dec 2023 13:37:57 +0100 | Subject | Re: [PATCH v4 2/2] mmc: mediatek: extend number of tuning steps | From | AngeloGioacchino Del Regno <> |
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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@mediatek.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
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