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 Cc: Jagan Teki jagannadh.teki@gmail.com --- So going through and cleaning up some of my trees and determining which patches have not been taken. A little more justification for this patch - I've gone through all of the current SPI implementations and have determined what (if any) support the driver has for half duplex operation by giving NULL for one of the two buffers (din/dout). This greatly reduces the need for temporary buffers for writing or reading large amounts of half-duplex data to devices over SPI. Here's the list:
altera_spi.c - SUPPORTS NULL din or dout andes_spi.c - REQUIRES NULL din or dout armada100_spi.c - SUPPORTS NULL din or dout atmel_spi.c - SUPPORTS NULL din or dout bfin_spi6xx.c - SUPPORTS NULL din or dout bfin_spi.c - SUPPORTS NULL din or dout cf_qspi.c - SUPPORTS NULL din or dout cf_spi.c - SUPPORTS NULL din or dout davinci_spi.c - SUPPORTS NULL din or dout exynos_spi.c - SUPPORTS NULL din or dout fdt_spi.c-tegra20_sf - SUPPORTS NULL din or dout fdt_spi.c-tegra20_sl - SUPPORTS NULL din or dout fdt_spi.c-tegra114 - SUPPORTS NULL din or dout fsl_espi.c - SUPPORTS NULL din (NOT dout) ftssp010_spi.c - SUPPORTS NULL din or dout ich.c - SUPPORTS NULL din or dout kirkwood_spi.c - SUPPORTS NULL din or dout mpc52xx_spi.c - NO SUPPORT mpc8xxx_spi.c - NO SUPPORT mxc_spi.c - NO SUPPORT mxs_spi.c - REQUIRES NULL din or dout oc_tiny_spi.c - SUPPORTS NULL din or dout omap3_spi.c - SUPPORTS NULL din or dout sandbox_spi.c - SUPPORTS NULL din or dout sh_qspi.c - SUPPORTS NULL din or dout sh_spi.c - SUPPORTS NULL din or dout soft_spi.c - NO SUPPORT ti_qspi.c - SUPPORTS NULL din or dout xilinx_spi.c - SUPPORTS NULL din or dout zynq_spi.c - SUPPORTS NULL din or dout
Furthermore, this would not affect any board already using temporary buffers and it would continue to work as usual. The *only* obscure corner case that this will not work is if NULL (0x0) is a valid buffer address in your system and you are transferring SPI to/from it. This seems very unlikely and would probably break in other ways from library functions that check their arguments.
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);