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spi: soft_spi: Support NULL din/dout buffers 

This mirrors the conventions used in other SPI drivers (kirkwood,
davinci, atmel, et al) where the din/dout buffer can be NULL when the
received/transmitted data isn't important.  This reduces the need for
allocating additional buffers when write-only/read-only functionality is
needed.

In the din == NULL case, the received data is simply not stored.  In the
dout == NULL case, zeroes are transmitted.

Signed-off-by: Andrew Ruder <andrew.ruder@elecsyscorp.com>
Cc: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Reviewed-by: Jagannadha Sutradharudu Teki <jaganna@xilinx.com>
This commit is contained in:
Andrew Ruder 2014-04-24 13:39:32 -05:00 committed by Jagannadha Sutradharudu Teki
parent 0472808608
commit c1c0dd2644
1 changed files with 12 additions and 6 deletions
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18
drivers/spi/soft_spi.c
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@ -136,10 +136,14 @@ int spi_xfer(struct spi_slave *slave, unsigned int bitlen,
/* /*
* Check if it is time to work on a new byte. * Check if it is time to work on a new byte.
*/ */
if((j % 8) == 0) { if ((j % 8) == 0) {
tmpdout = *txd++; if (txd)
tmpdout = *txd++;
else
tmpdout = 0;
if(j != 0) { if(j != 0) {
*rxd++ = tmpdin; if (rxd)
*rxd++ = tmpdin;
} }
tmpdin = 0; tmpdin = 0;
} }
@ -164,9 +168,11 @@ int spi_xfer(struct spi_slave *slave, unsigned int bitlen,
* bits over to left-justify them. Then store the last byte * bits over to left-justify them. Then store the last byte
* read in. * read in.
*/ */
if((bitlen % 8) != 0) if (rxd) {
tmpdin <<= 8 - (bitlen % 8); if ((bitlen % 8) != 0)
*rxd++ = tmpdin; tmpdin <<= 8 - (bitlen % 8);
*rxd++ = tmpdin;
}
if (flags & SPI_XFER_END) if (flags & SPI_XFER_END)
spi_cs_deactivate(slave); spi_cs_deactivate(slave);