Hi All,
I want to ask what the correct USB behavior should be for a gadget
attempting to perform a zero byte transfer (note transfer, not
transaction) on a bulk-in endpoint should be:
Background:
* Basically I've got a hacked up kernel; hardware is TI omap dm3730
(an overo gumstix board).
* I use gadget fs (for which I've done major work to fix both
gadgetfs and musb).
* I connect the overo board to a windows/linux/osx pc via its OTG port.
I discovered that by writing a zero length packet to a bulk in
endpoint I can cause a kernel panic in musb - basically I think it is
trying to setup a DMA transaction with a "valid" pointer of zero bytes
and blowing up. I encountered this by writing a crappy user-land
program (by accident). Now I don't believe I should be able to panic
the kernel from my stupid user program; so I could easily short-cut this
so that gadgetfs disallows zero byte writes. I could also pursue this
lower so that musb does not allow 0 length transactions - however, my
question is more basic than that:
Are zero length transfers from a device to the PC on a bulk endpoint
sensible?
I can see a case where a zero length transfer would cause a read
thread in the host to be interrupted.
Does musb/gadgetfs need to correctly support zero byte transfers, or
is this a non-sensible suggestion?
Cheers,
-Brett
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