[U-Boot] Debugging, Why USB is not stable

[Detlev Zundel <dzu@denx.de>]

Hi G?rald,

> I have some few problems with usb start / reset commands on last uboot.
>
> USB hard drive are not always detected.
>
> Is there something I missed ?

Only the fact that USB is a nightmare to work with.  No, honestly, we
have a continuous stream of USB related problems with the current USB
code.  As I understand it this results from the ever more diverging USB
implementation in U-Boot and e.g. in the Linux kernel.  The latter has
received a lot of work which is simply not possible by reading
datasheets and writing software according to those.  This involves a lot
of testing on literally thousands of different HW incarnations and on
working around the discovered idosyncracies of the parts.

Sometimes I get the impression that we would save a lot of headache by
starting afresh and porting the current Linux code into U-Boot thus
leverage all this, but nobody yet dared to start such a feat.

For the problem at hand, you may try to test variations on your setup,
e.g. by introducing different hubs in different combinations.  I'm
pretty sure that this will change the situation - sadly may be not for
the better.

Cheers
  Detlev

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