On 2018/5/4 22:50, Wolfram Sang wrote:
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?
The hardware should at least has a little mergin window for passing the
tuning. If it fails, the HW is questionable that how could you know if
the following slower data transfer could work reliably. That hides the
HW problem more deeply. But if you mean the HW itself can't support, for
instance HS200, that's another question for why folks still add these
caps to the DT.
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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