[RFC 2/2] spi: spi-gpio: add SPI_3WIRE support

[Lorenzo Bianconi <lorenzo.bianconi@xxxxxxxxxx>]

Add SPI_3WIRE support to spi-gpio controller introducing
set_line_direction function pointer in spi_bitbang data structure.
Spi-gpio controller in 3wire mode has been tested using hts221 temp/rh
iio sensor

Signed-off-by: Lorenzo Bianconi <lorenzo.bianconi@xxxxxxxxxx>
---
 drivers/spi/spi-bitbang.c       | 14 ++++++++++++++
 drivers/spi/spi-gpio.c          | 17 ++++++++++++++++-
 include/linux/spi/spi_bitbang.h |  1 +
 3 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/drivers/spi/spi-bitbang.c b/drivers/spi/spi-bitbang.c
index 76f1b534bdd7..8c98a2acc59a 100644
--- a/drivers/spi/spi-bitbang.c
+++ b/drivers/spi/spi-bitbang.c
@@ -244,6 +244,20 @@ static int spi_bitbang_bufs(struct spi_device *spi, struct spi_transfer *t)
 	struct spi_bitbang_cs	*cs = spi->controller_state;
 	unsigned		nsecs = cs->nsecs;
 
+	if (spi->mode & SPI_3WIRE) {
+		struct spi_bitbang *bitbang;
+		unsigned flags;
+		int err;
+
+		bitbang = spi_master_get_devdata(spi->master);
+		err = bitbang->set_line_direction(spi, !!(t->tx_buf));
+		if (err < 0)
+			return err;
+
+		flags = t->tx_buf ? SPI_MASTER_NO_RX : SPI_MASTER_NO_TX;
+		return cs->txrx_bufs(spi, cs->txrx_word, nsecs, t, flags);
+	}
+
 	return cs->txrx_bufs(spi, cs->txrx_word, nsecs, t, 0);
 }
 
diff --git a/drivers/spi/spi-gpio.c b/drivers/spi/spi-gpio.c
index be68298cbd9c..0626e6e3ea0c 100644
--- a/drivers/spi/spi-gpio.c
+++ b/drivers/spi/spi-gpio.c
@@ -121,7 +121,10 @@ static inline int getmiso(const struct spi_device *spi)
 {
 	struct spi_gpio *spi_gpio = spi_to_spi_gpio(spi);
 
-	return !!gpiod_get_value_cansleep(spi_gpio->miso);
+	if (spi->mode & SPI_3WIRE)
+		return !!gpiod_get_value_cansleep(spi_gpio->mosi);
+	else
+		return !!gpiod_get_value_cansleep(spi_gpio->miso);
 }
 
 /*
@@ -250,6 +253,16 @@ static int spi_gpio_setup(struct spi_device *spi)
 	return status;
 }
 
+static int spi_gpio_set_direction(struct spi_device *spi, bool output)
+{
+	struct spi_gpio *spi_gpio = spi_to_spi_gpio(spi);
+
+	if (output)
+		return gpiod_direction_output(spi_gpio->mosi, 1);
+	else
+		return gpiod_direction_input(spi_gpio->mosi);
+}
+
 static void spi_gpio_cleanup(struct spi_device *spi)
 {
 	spi_bitbang_cleanup(spi);
@@ -395,6 +408,7 @@ static int spi_gpio_probe(struct platform_device *pdev)
 		return status;
 
 	master->bits_per_word_mask = SPI_BPW_RANGE_MASK(1, 32);
+	master->mode_bits = SPI_3WIRE | SPI_CPHA | SPI_CPOL;
 	master->flags = master_flags;
 	master->bus_num = pdev->id;
 	/* The master needs to think there is a chipselect even if not connected */
@@ -407,6 +421,7 @@ static int spi_gpio_probe(struct platform_device *pdev)
 
 	spi_gpio->bitbang.master = master;
 	spi_gpio->bitbang.chipselect = spi_gpio_chipselect;
+	spi_gpio->bitbang.set_line_direction = spi_gpio_set_direction;
 
 	if ((master_flags & (SPI_MASTER_NO_TX | SPI_MASTER_NO_RX)) == 0) {
 		spi_gpio->bitbang.txrx_word[SPI_MODE_0] = spi_gpio_txrx_word_mode0;
diff --git a/include/linux/spi/spi_bitbang.h b/include/linux/spi/spi_bitbang.h
index 5847f00ef9cf..b7e021b274dc 100644
--- a/include/linux/spi/spi_bitbang.h
+++ b/include/linux/spi/spi_bitbang.h
@@ -31,6 +31,7 @@ struct spi_bitbang {
 	u32	(*txrx_word[4])(struct spi_device *spi,
 			unsigned nsecs,
 			u32 word, u8 bits, unsigned flags);
+	int	(*set_line_direction)(struct spi_device *spi, bool output);
 };
 
 /* you can call these default bitbang->master methods from your custom
-- 
2.18.0

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