Zero-Byte Packet Questions

Hello,

We had the following questions for a peripheral controller driver. We
do have an idea about some of the answers, evidently our understanding
is not complete.

1. The gadget can ask the peripheral controller to send/receive zero
byte packets. Consider the following sub-cases:
        a) req.zero : When set we have to send zero byte packet.
        b) Similarly, when req.length = 0, zero length packets, have
to be sent/rcvd.
Why do have both of these, why a duplication ? Is it possible that we
have a length set to some value and a req.zero also set ?

2. During a bulk xaction, if the size of transfer is equal to the max
packet size, then will the gadget queue a zero byte packet. Or is it
the peripheral's driver responsibility to send a zero byte packet. If
the former is a yes, then how is it accomplished ? Is a req.zero set
or length = 0 ?

3. Do I have a request form the upper layer for a zero byte packet,
for a control xfer when the data stage is an 'OUT' stage ? If yes, why
?

4. Why use alloc_buffer call? I am not interested in doing any DMA.
This DMA is between what & what? Who uses these buffers ?

Thanks & Regards.

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