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    SubjectRe: [patch 2.6.28-rc9] spi: spi_write_then_read() regression fix


    On Sat, 20 Dec 2008, David Brownell wrote:
    >
    > All SPI transfers are full duplex, and are packaged as half duplex
    > by either discarding the data that's read ("write only"), or else
    > by writing zeroes ("read only"). That patch wasn't ensuring that
    > zeroes were getting written out during the "half duplex read" part
    > of the transaction; instead, old RX bits were getting sent.

    Hmm. In addition, isn't this broken (in that same function):

    memcpy(local_buf, txbuf, n_tx);
    x.tx_buf = local_buf;
    x.rx_buf = local_buf;

    /* do the i/o */
    status = spi_sync(spi, &message);
    if (status == 0)
    memcpy(rxbuf, x.rx_buf + n_tx, n_rx);

    shouldn't that 'rx_buf' setup be

    x.rx_buf = local_buf + n_tx;

    since the whole point was that we allocated a buffer that can hold _both_
    the rx and tx parts? Especially as that final copy into the resulting
    "rxbuf" thing uses that "+ n_tx" addition?

    Linus


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