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 --- drivers/spi/soft_spi.c | 18 +++++++++++++----- 1 file changed, 13 insertions(+), 5 deletions(-)
diff --git a/drivers/spi/soft_spi.c b/drivers/spi/soft_spi.c index 5d22351..5fdd091 100644 --- a/drivers/spi/soft_spi.c +++ b/drivers/spi/soft_spi.c @@ -137,9 +137,15 @@ int spi_xfer(struct spi_slave *slave, unsigned int bitlen, * Check if it is time to work on a new byte. */ if((j % 8) == 0) { - tmpdout = *txd++; + if (txd) { + tmpdout = *txd++; + } else { + tmpdout = 0; + } if(j != 0) { - *rxd++ = tmpdin; + if (rxd) { + *rxd++ = tmpdin; + } } tmpdin = 0; } @@ -164,9 +170,11 @@ int spi_xfer(struct spi_slave *slave, unsigned int bitlen, * bits over to left-justify them. Then store the last byte * read in. */ - if((bitlen % 8) != 0) - tmpdin <<= 8 - (bitlen % 8); - *rxd++ = tmpdin; + if (rxd) { + if((bitlen % 8) != 0) + tmpdin <<= 8 - (bitlen % 8); + *rxd++ = tmpdin; + }
if (flags & SPI_XFER_END) spi_cs_deactivate(slave);