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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?


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