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spi/mpc512x-psc: optionally keep PSC SS asserted across xfer segmensts

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Some SPI slave devices require asserted chip select signal across
multiple transfer segments of an SPI message. Currently the driver
always de-asserts the internal SS signal for every single transfer
segment of the message and ignores the 'cs_change' flag of the
transfer description. Disable the internal chip select (SS) only
if this is needed and indicated by the 'cs_change' flag.

Without this change, each partial transfer of a surrounding
multi-part SPI transaction might erroneously change the SS
signal, which might prevent slaves from answering the request
that was sent in a previous transfer segment because the
transaction could be considered aborted (SS was de-asserted
before reading the response).

Reported-by: Gerhard Sittig <gerhard.sittig@ifm.com>
Signed-off-by: Anatolij Gustschin <agust@denx.de>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Cc: stable@vger.kernel.org
This commit is contained in:
Anatolij Gustschin 2013-03-13 14:57:43 +01:00 committed by Mark Brown
parent b0b36b861e
commit 1ad849aee5
1 changed files with 1 additions and 1 deletions
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2
drivers/spi/spi-mpc512x-psc.c
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@ -164,7 +164,7 @@ static int mpc512x_psc_spi_transfer_rxtx(struct spi_device *spi,
for (i = count; i > 0; i--) {
data = tx_buf ? *tx_buf++ : 0;
if (len == EOFBYTE)
if (len == EOFBYTE && t->cs_change)
setbits32(&fifo->txcmd, MPC512x_PSC_FIFO_EOF);
out_8(&fifo->txdata_8, data);
len--;