Why no fallback when tuning fails?

[Wolfram Sang <wsa@xxxxxxxxxxxxx>]

Hi,

I really wonder about this: For both, MMC and SD, the MMC core bails out
when tuning fails, i.e. we remove the card and report the error to the
upper layers. Why don't we fall back to a slower speed which doesn't
need tuning instead?

I have seen this happening with HW failing to do the tuning. But I also
"emulated" it by simply returning -EINVAL at the beginning of the
execute_tuning callback of the driver.

For people, having their rootfs on an HS200/400 capable eMMC, such a
tuning failure means OOPS instead of just a slower speed.

Is this intentional? Can we change this? Did I miss something?

Thanks,

   Wolfram

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