[PATCH v4 3/3] i2c: gpio: support write-only sda/scl w/o pull-up

[Heiner Kallweit <hkallweit1@gmail.com>]

There are slave devices that understand I2C but have read-only SDA and
SCL. Examples are FD650 7-segment LED controller and its derivatives.
Typical board designs don't even have a pull-up for both pins.
Handle the new attributes for write-only SDA and missing pull-up on
SDA/SCL.

For either pin the open-drain and has-no-pullup properties are
mutually-exclusive, what is documented in the DT property documentation.
We don't add an extra warning here because the open-drain properties
are marked deprecated anyway.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
---
v3:
- improve description of attribute sda_is_output_only
v4:
- handle new no-pullup attributes
---
 drivers/i2c/busses/i2c-gpio.c          | 13 ++++++++++---
 include/linux/platform_data/i2c-gpio.h |  9 +++++++++
 2 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/drivers/i2c/busses/i2c-gpio.c b/drivers/i2c/busses/i2c-gpio.c
index 0e4385a9b..85b3beb20 100644
--- a/drivers/i2c/busses/i2c-gpio.c
+++ b/drivers/i2c/busses/i2c-gpio.c
@@ -316,6 +316,12 @@ static void of_i2c_gpio_get_props(struct device_node *np,
 		of_property_read_bool(np, "i2c-gpio,scl-open-drain");
 	pdata->scl_is_output_only =
 		of_property_read_bool(np, "i2c-gpio,scl-output-only");
+	pdata->sda_is_output_only =
+		of_property_read_bool(np, "i2c-gpio,sda-output-only");
+	pdata->sda_has_no_pullup =
+		of_property_read_bool(np, "i2c-gpio,sda-has-no-pullup");
+	pdata->scl_has_no_pullup =
+		of_property_read_bool(np, "i2c-gpio,scl-has-no-pullup");
 }
 
 static struct gpio_desc *i2c_gpio_get_desc(struct device *dev,
@@ -392,7 +398,7 @@ static int i2c_gpio_probe(struct platform_device *pdev)
 	 * handle them as we handle any other output. Else we enforce open
 	 * drain as this is required for an I2C bus.
 	 */
-	if (pdata->sda_is_open_drain)
+	if (pdata->sda_is_open_drain || pdata->sda_has_no_pullup)
 		gflags = GPIOD_OUT_HIGH;
 	else
 		gflags = GPIOD_OUT_HIGH_OPEN_DRAIN;
@@ -400,7 +406,7 @@ static int i2c_gpio_probe(struct platform_device *pdev)
 	if (IS_ERR(priv->sda))
 		return PTR_ERR(priv->sda);
 
-	if (pdata->scl_is_open_drain)
+	if (pdata->scl_is_open_drain || pdata->scl_has_no_pullup)
 		gflags = GPIOD_OUT_HIGH;
 	else
 		gflags = GPIOD_OUT_HIGH_OPEN_DRAIN;
@@ -418,7 +424,8 @@ static int i2c_gpio_probe(struct platform_device *pdev)
 
 	if (!pdata->scl_is_output_only)
 		bit_data->getscl = i2c_gpio_getscl;
-	bit_data->getsda = i2c_gpio_getsda;
+	if (!pdata->sda_is_output_only)
+		bit_data->getsda = i2c_gpio_getsda;
 
 	if (pdata->udelay)
 		bit_data->udelay = pdata->udelay;
diff --git a/include/linux/platform_data/i2c-gpio.h b/include/linux/platform_data/i2c-gpio.h
index a907774fd..545639bcc 100644
--- a/include/linux/platform_data/i2c-gpio.h
+++ b/include/linux/platform_data/i2c-gpio.h
@@ -16,16 +16,25 @@
  *	isn't actively driven high when setting the output value high.
  *	gpio_get_value() must return the actual pin state even if the
  *	pin is configured as an output.
+ * @sda_is_output_only: SDA output drivers can't be turned off.
+ *	This is for clients that can only read SDA/SCL.
+ * @sda_has_no_pullup: SDA is used in a non-compliant way and has no pull-up.
+ *	Therefore disable open-drain.
  * @scl_is_open_drain: SCL is set up as open drain. Same requirements
  *	as for sda_is_open_drain apply.
  * @scl_is_output_only: SCL output drivers cannot be turned off.
+ * @scl_has_no_pullup: SCL is used in a non-compliant way and has no pull-up.
+ *	Therefore disable open-drain.
  */
 struct i2c_gpio_platform_data {
 	int		udelay;
 	int		timeout;
 	unsigned int	sda_is_open_drain:1;
+	unsigned int	sda_is_output_only:1;
+	unsigned int	sda_has_no_pullup:1;
 	unsigned int	scl_is_open_drain:1;
 	unsigned int	scl_is_output_only:1;
+	unsigned int	scl_has_no_pullup:1;
 };
 
 #endif /* _LINUX_I2C_GPIO_H */
-- 
2.39.0