[U-Boot] [PATCH 1/4] spi: spi-mem: Add optional half-duplex SPI transfer mode

[Boris Brezillon <boris.brezillon@bootlin.com>]

On Tue, 7 Aug 2018 07:06:58 +0200
Stefan Roese <sr@denx.de> wrote:

> Hi Boris,
> 
> On 06.08.2018 21:53, Boris Brezillon wrote:
> > Hi Stefan,
> > 
> > On Mon,  6 Aug 2018 17:12:50 +0200
> > Stefan Roese <sr@denx.de> wrote:
> >   
> >> Some SPI controller might now support full-duplex SPI transfers.
> >> This option can be enabled to use half-duplex operation mode for
> >> such SPI controllers.
> >>
> >> Signed-off-by: Stefan Roese <sr@denx.de>
> >> Cc: Miquel Raynal <miquel.raynal@bootlin.com>
> >> Cc: Boris Brezillon <boris.brezillon@bootlin.com>
> >> Cc: Jagan Teki <jagan@openedev.com>
> >> ---
> >>   drivers/spi/Kconfig   |  8 ++++++++
> >>   drivers/spi/spi-mem.c | 31 ++++++++++++++++++++++++++++---
> >>   2 files changed, 36 insertions(+), 3 deletions(-)
> >>
> >> diff --git a/drivers/spi/Kconfig b/drivers/spi/Kconfig
> >> index 9fbd26740d..5bd8289284 100644
> >> --- a/drivers/spi/Kconfig
> >> +++ b/drivers/spi/Kconfig
> >> @@ -25,6 +25,14 @@ config SPI_MEM
> >>   	  This extension is meant to simplify interaction with SPI memories
> >>   	  by providing an high-level interface to send memory-like commands.
> >>   
> >> +config SPI_MEM_HALF_DUPLEX
> >> +	bool "Use half-duplex SPI transfer"
> >> +	depends on SPI_MEM
> >> +	help
> >> +	  Some SPI controller might not support full-duplex SPI transfers.
> >> +	  This option can be enabled to use half-duplex operation mode for
> >> +	  such SPI controllers.
> >> +
> >>   config ALTERA_SPI
> >>   	bool "Altera SPI driver"
> >>   	help
> >> diff --git a/drivers/spi/spi-mem.c b/drivers/spi/spi-mem.c
> >> index 07ce799170..617fbbfe09 100644
> >> --- a/drivers/spi/spi-mem.c
> >> +++ b/drivers/spi/spi-mem.c
> >> @@ -202,6 +202,10 @@ int spi_mem_exec_op(struct spi_slave *slave, const struct spi_mem_op *op)
> >>   	struct dm_spi_ops *ops = spi_get_ops(bus);
> >>   	unsigned int xfer_len, pos = 0;
> >>   	u8 *tx_buf, *rx_buf = NULL;
> >> +	unsigned int pos2;
> >> +	int tx_len;
> >> +	int rx_len;
> >> +	u32 flag;
> >>   	int ret;
> >>   	int i;
> >>   
> >> @@ -370,8 +374,29 @@ int spi_mem_exec_op(struct spi_slave *slave, const struct spi_mem_op *op)
> >>   	if (tx_data)
> >>   		memcpy(tx_buf + pos, op->data.buf.out, op->data.nbytes);
> >>   
> >> -	ret = spi_xfer(slave, xfer_len * 8, tx_buf, rx_buf,
> >> -		       SPI_XFER_BEGIN | SPI_XFER_END);
> >> +	pos2 = pos;
> >> +	if (CONFIG_IS_ENABLED(SPI_MEM_HALF_DUPLEX)) {
> >> +		if (rx_data) {
> >> +			tx_len = (sizeof(op->cmd.opcode) +
> >> +				  op->addr.nbytes + op->dummy.nbytes);
> >> +			rx_len = op->data.nbytes;
> >> +			flag = SPI_XFER_BEGIN;
> >> +			pos2 = 0;
> >> +		} else {
> >> +			tx_len = xfer_len;
> >> +			rx_len = 0;
> >> +			flag = SPI_XFER_BEGIN | SPI_XFER_END;
> >> +		}
> >> +		ret = spi_xfer(slave, tx_len * 8, tx_buf, NULL, flag);
> >> +		if (rx_data) {
> >> +			ret = spi_xfer(slave, rx_len * 8, NULL,
> >> +				       rx_buf, SPI_XFER_END);
> >> +		}  
> > 
> > Why not doing that all the time and split things in 3 transfers
> > instead of 2:
> > 
> > 1/ the opcode + address + dummy cycles
> > 2/ the tx data
> > 3/ the rx data (optional)

Actually it's:

1/ the opcode + address + dummy cycles
2/ tx or rx data (optional)

but I guess you figured this out already.