How to extract opcode, addr, dummy and buffer in transfer_one_message()?

[Stefan Schaeckeler <schaecsn@xxxxxxx>]

Hello linux-spi,

I can implement mem_ops() a/o transfer_one_message().

spi-mem.c:spi_mem_exec_op() will directly pass op to mem_ops->exec_op(). There
I can easily extract opcode, addr, dummy and data buffer. It would probably
look roughly like

exec_op(struct spi_mem *mem, const struct spi_mem_op *op){
        dummy = addr = -1;

        opcode = op->cmd.opcode;

        addrlen=op->addr.nbytes;
        if (addrlen)
            addr = op->addr.val;

        if (op->dummy.nbytes)
            dummy = QSPI_DUMMY_CYCLE;

        len=op->data.nbytes;
        if (len)
            if (op->data.dir == SPI_MEM_DATA_IN) {
                rxbuf = op->data.buf.in;
                is_wr = false;
            } else {
                txbuf = op->data.buf.out;
                is_wr = true;
            }
}

That's great. What about transfer_one_message()?

spi-mem.c:spi_mem_exec_op() builds a message consisting of multiple transfers.
If there is no address, dummy or data buffer, then they will not be included in
the transfer array as transfers are created like this

        /* op is the first transfer */
        tmpbuf[0] = op->cmd.opcode;
        xfers[xferpos].tx_buf = tmpbuf;
        ...

        if (op->addr.nbytes) {
        /* add addr transfer */
        ...
        }

        if (op->dummy.nbytes) {
        /* add dummy transfer */
        ...
        }

        if (op->data.nbytes) {
        /* add data transfer */
        ...
        }

These transfers are then passed as a message consisting of 1 to 4 transfers to
transfer_one_message().

In transfer_one_message(), the first transfer is the opcode. How do I now what
the next transfers represent? Like in the exec_op() example above, I would like
to create and initialize my variables opcode, addr, dummy and read or write
buffer.


Related question: what are the disadvantages of always using mem_ops() and
never transfer_one_message()?

Thanks,
 Stefan