[Bug 220491] usb_storage connected SD card disconnects/reconnects on resume from suspend

[bugzilla-daemon@kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=220491

--- Comment #20 from Alan Stern (stern@rowland.harvard.edu) ---
When devices "reliably disconnect/reconnect" on the emb-qm77 system, do they
work reliably afterward?  Always, sometimes, or never?

Remember, the traces you have collected so far on the Samsung machine show the
card reader device disconnecting/reconnecting on every suspend -- but on some
of them it worked afterward and on some it did not.

I agree that it would be good to solve this problem somehow in the kernel. 
However, at this point we do not know enough about what is going wrong to tell
if this is even possible, let alone how to do it.  For all we know, the problem
might be fixed by something as simple as adding a 10-ms delay during the resume
procedure.

Also, I don't fully understand what you mean by "extend the linux kernel's
usb_persist mechanism to encompass disconnection and reconnection of USB 3.0
devices".  That's what it does right now -- in the case where the card reader
worked following suspend/resume, it was because the device disconnected and
reconnected and the usb-persist mechanism was successful.  (In the cases where
the card reader didn't work following suspend/resume, it was because the device
disconnected and reconnected and then so many other errors occurred that the
usb-persist mechanism was unable to cope and thus failed.)

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