Re: [PATCH 2/4] spi: gpio: Fix reading for 3WIRE

[Lorenzo Bianconi <lorenzo.bianconi@xxxxxxxxxx>]

> If he GPIO bitbanged host is registered using just one line,
> MISO, naturally the DT parser will flag the host as
> SPI_MASTER_NO_RX.
> 
> This makes the GPIO SPI driver assign word transfer functions
> that enforce the SPI master flags SPI_MASTER_NO_RX (or
> SPI_MASTER_NO_TX) to the flags on each call down to the
> inlined bitbang functions such as bitbang_txrx_be_cpha0().
> 
> In the 3WIRE case, enforcing this flag is wrong, because the
> master can then do both TX and RX (albeit not at the same time)
> using the same line, by just switching the direction of the
> line and keep clocking in bits.
> 
> Augment spi_gpio_spec_txrx_word_mode[0123] to account for
> this.
> 
> Cc: Andrzej Hajda <a.hajda@xxxxxxxxxxx>
> Cc: Lorenzo Bianconi <lorenzo.bianconi@xxxxxxxxxx>
> Signed-off-by: Linus Walleij <linus.walleij@xxxxxxxxxx>
> ---
>  drivers/spi/spi-gpio.c | 17 +++++++++++++----
>  1 file changed, 13 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/spi/spi-gpio.c b/drivers/spi/spi-gpio.c
> index 9f4882f82c3c..6bd692304b92 100644
> --- a/drivers/spi/spi-gpio.c
> +++ b/drivers/spi/spi-gpio.c
> @@ -183,33 +183,42 @@ static u32 spi_gpio_txrx_word_mode3(struct spi_device *spi,
>   * speed in the generic case (when both MISO and MOSI lines are
>   * available), as optimiser will remove the checks when argument is
>   * constant.
> + *
> + * A special kludge is needed for 3WIRE SPI, as this mode can use
> + * the same line for RX and TX and should not enforce the host
> + * flag - we will just switch MISO from output to input mode when
> + * needed.
>   */
>  

Acked-by: Lorenzo Bianconi <lorenzo.bianconi@xxxxxxxxxx>