Applied "spi: gpio: Support 3WIRE high-impedance turn-around" to the spi tree

Commit Message

Mark Brown Nov. 7, 2018, 4:22 p.m. UTC

The patch

   spi: gpio: Support 3WIRE high-impedance turn-around

has been applied to the spi tree at

   https://git.kernel.org/pub/scm/linux/kernel/git/broonie/spi.git 

All being well this means that it will be integrated into the linux-next
tree (usually sometime in the next 24 hours) and sent to Linus during
the next merge window (or sooner if it is a bug fix), however if
problems are discovered then the patch may be dropped or reverted.  

You may get further e-mails resulting from automated or manual testing
and review of the tree, please engage with people reporting problems and
send followup patches addressing any issues that are reported if needed.

If any updates are required or you are submitting further changes they
should be sent as incremental updates against current git, existing
patches will not be replaced.

Please add any relevant lists and maintainers to the CCs when replying
to this mail.

Thanks,
Mark

From 5132b3d283710d196cd8af99b5585507e8b30709 Mon Sep 17 00:00:00 2001
From: Linus Walleij <[e-mail]>
Date: Thu, 1 Nov 2018 22:25:04 +0100
Subject: [PATCH] spi: gpio: Support 3WIRE high-impedance turn-around

Some devices such as the TPO TPG110 display panel require
a "high-impedance turn-around", in effect a clock cycle after
switching the line from output to input mode.

Support this in the GPIO driver to begin with. Other driver
may implement it if they can, it is unclear if this can
be achieved with anything else than GPIO bit-banging.

Cc: Andrzej Hajda <[e-mail]>
Acked-by: Lorenzo Bianconi <[e-mail]>
Signed-off-by: Linus Walleij <[e-mail]>
Signed-off-by: Mark Brown <[e-mail]>
---
 drivers/spi/spi-gpio.c  | 24 +++++++++++++++++++++---
 include/linux/spi/spi.h |  1 +
 2 files changed, 22 insertions(+), 3 deletions(-)

Patch

diff --git a/drivers/spi/spi-gpio.c b/drivers/spi/spi-gpio.c
index 45973ee3ae11..a4aee26028cd 100644
--- a/drivers/spi/spi-gpio.c
+++ b/drivers/spi/spi-gpio.c
@@ -256,11 +256,29 @@  static int spi_gpio_setup(struct spi_device *spi)
 static int spi_gpio_set_direction(struct spi_device *spi, bool output)
 {
 	struct spi_gpio *spi_gpio = spi_to_spi_gpio(spi);
+	int ret;
 
 	if (output)
 		return gpiod_direction_output(spi_gpio->mosi, 1);
-	else
-		return gpiod_direction_input(spi_gpio->mosi);
+
+	ret = gpiod_direction_input(spi_gpio->mosi);
+	if (ret)
+		return ret;
+	/*
+	 * Send a turnaround high impedance cycle when switching
+	 * from output to input. Theoretically there should be
+	 * a clock delay here, but as has been noted above, the
+	 * nsec delay function for bit-banged GPIO is simply
+	 * {} because bit-banging just doesn't get fast enough
+	 * anyway.
+	 */
+	if (spi->mode & SPI_3WIRE_HIZ) {
+		gpiod_set_value_cansleep(spi_gpio->sck,
+					 !(spi->mode & SPI_CPOL));
+		gpiod_set_value_cansleep(spi_gpio->sck,
+					 !!(spi->mode & SPI_CPOL));
+	}
+	return 0;
 }
 
 static void spi_gpio_cleanup(struct spi_device *spi)
@@ -410,7 +428,7 @@  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->mode_bits = SPI_3WIRE | SPI_3WIRE_HIZ | 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 */
diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index 6be77fa5ab90..3ced58eebe1b 100644
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -155,6 +155,7 @@  struct spi_device {
 #define	SPI_RX_DUAL	0x400			/* receive with 2 wires */
 #define	SPI_RX_QUAD	0x800			/* receive with 4 wires */
 #define SPI_CS_WORD	0x1000			/* toggle cs after each word */
+#define	SPI_3WIRE_HIZ	0x2000			/* high impedance turnaround */
 	int			irq;
 	void			*controller_state;
 	void			*controller_data;