[PATCH v4 0/3] i2c: gpio: support write-only sda

[PATCH v4 0/3] i2c: gpio: support write-only sda

[Heiner Kallweit]

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.
Therefore add properties for not using open-drain. For write-only SCL
we have a property already, add one for write-only SDA.

v2:
- improve commit message for patch 1

v3:
- patch 2: check for adap->getsda in readbytes()
- patch 2: align warning message level for info on missing getscl/getsda
- patch 3: improve description of attribute sda_is_output_only

v4:
- patch 1: add no-pullup properties
- patch 2: handle SDA and SCL independently
- patch 2: properly handle case that SDA is NULL but SCL not
- patch 3: handle new no-pullup attributes

Heiner Kallweit (3):
  dt-bindings: i2c-gpio: Add properties for dealing with write-only SDA/SCL w/o pullup
  i2c: algo: bit: allow getsda to be NULL
  i2c: gpio: support write-only sda/scl w/o pull-up

 .../devicetree/bindings/i2c/i2c-gpio.yaml     | 16 ++++
 drivers/i2c/algos/i2c-algo-bit.c              | 77 +++++++++----------
 drivers/i2c/busses/i2c-gpio.c                 | 13 +++-
 include/linux/platform_data/i2c-gpio.h        |  9 +++
 4 files changed, 70 insertions(+), 45 deletions(-)

-- 
2.39.0

[PATCH v4 1/3] dt-bindings: i2c-gpio: Add properties for dealing with write-only SDA/SCL w/o pullup

[Heiner Kallweit]

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.
Therefore add properties for not using open-drain. For write-only SCL
we have a property already, add one for write-only SDA.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
---
v4:
- add no-pullup properties
---
 .../devicetree/bindings/i2c/i2c-gpio.yaml        | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/Documentation/devicetree/bindings/i2c/i2c-gpio.yaml b/Documentation/devicetree/bindings/i2c/i2c-gpio.yaml
index e0d76d5eb..67898cc52 100644
--- a/Documentation/devicetree/bindings/i2c/i2c-gpio.yaml
+++ b/Documentation/devicetree/bindings/i2c/i2c-gpio.yaml
@@ -33,6 +33,10 @@ properties:
       open drain.
     maxItems: 1
 
+  i2c-gpio,sda-output-only:
+    description: sda as output only
+    type: boolean
+
   i2c-gpio,scl-output-only:
     description: scl as output only
     type: boolean
@@ -63,6 +67,18 @@ properties:
       GPIO line used for SCL into open drain mode, and that something is not
       the GPIO chip. It is essentially an inconsistency flag.
 
+  i2c-gpio,sda-has-no-pullup:
+    type: boolean
+    description: sda is used in a non-compliant way and has no pull-up.
+      Therefore disable open-drain. This property is mutually-exclusive
+      with i2c-gpio,sda-open-drain.
+
+  i2c-gpio,scl-has-no-pullup:
+    type: boolean
+    description: scl is used in a non-compliant way and has no pull-up.
+      Therefore disable open-drain. This property is mutually-exclusive
+      with i2c-gpio,scl-open-drain.
+
 required:
   - compatible
   - sda-gpios
-- 
2.39.0

[PATCH v4 2/3] i2c: algo: bit: allow getsda to be NULL

[Heiner Kallweit]

This is in preparation of supporting write-only SDA in i2c-gpio.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
---
v3:
- check for adap->getsda in readbytes()
- align warning message level for info on missing getscl/getsda
v4:
- handle SDA and SCL independently
- properly handle case that SDA is NULL but SCL not
---
 drivers/i2c/algos/i2c-algo-bit.c | 77 +++++++++++++++-----------------
 1 file changed, 35 insertions(+), 42 deletions(-)

diff --git a/drivers/i2c/algos/i2c-algo-bit.c b/drivers/i2c/algos/i2c-algo-bit.c
index fc90293af..eddf25b90 100644
--- a/drivers/i2c/algos/i2c-algo-bit.c
+++ b/drivers/i2c/algos/i2c-algo-bit.c
@@ -184,8 +184,9 @@ static int i2c_outb(struct i2c_adapter *i2c_adap, unsigned char c)
 
 	/* read ack: SDA should be pulled down by slave, or it may
 	 * NAK (usually to report problems with the data we wrote).
+	 * Always report ACK if SDA is write-only.
 	 */
-	ack = !getsda(adap);    /* ack: sda is pulled low -> success */
+	ack = !adap->getsda || !getsda(adap);    /* ack: sda is pulled low -> success */
 	bit_dbg(2, &i2c_adap->dev, "i2c_outb: 0x%02x %s\n", (int)c,
 		ack ? "A" : "NA");
 
@@ -238,71 +239,55 @@ static int test_bus(struct i2c_adapter *i2c_adap)
 			return -ENODEV;
 	}
 
+	if (adap->getsda == NULL)
+		pr_info("%s: SDA is write-only, testing not possible\n", name);
 	if (adap->getscl == NULL)
-		pr_info("%s: Testing SDA only, SCL is not readable\n", name);
+		pr_info("%s: SCL is write-only, testing not possible\n", name);
 
-	sda = getsda(adap);
-	scl = (adap->getscl == NULL) ? 1 : getscl(adap);
+	sda = adap->getsda ? getsda(adap) : 1;
+	scl = adap->getscl ? getscl(adap) : 1;
 	if (!scl || !sda) {
-		printk(KERN_WARNING
-		       "%s: bus seems to be busy (scl=%d, sda=%d)\n",
-		       name, scl, sda);
+		pr_warn("%s: bus seems to be busy (scl=%d, sda=%d)\n", name, scl, sda);
 		goto bailout;
 	}
 
 	sdalo(adap);
-	sda = getsda(adap);
-	scl = (adap->getscl == NULL) ? 1 : getscl(adap);
-	if (sda) {
-		printk(KERN_WARNING "%s: SDA stuck high!\n", name);
+	if (adap->getsda && getsda(adap)) {
+		pr_warn("%s: SDA stuck high!\n", name);
 		goto bailout;
 	}
-	if (!scl) {
-		printk(KERN_WARNING
-		       "%s: SCL unexpected low while pulling SDA low!\n",
-		       name);
+	if (adap->getscl && !getscl(adap)) {
+		pr_warn("%s: SCL unexpected low while pulling SDA low!\n", name);
 		goto bailout;
 	}
 
 	sdahi(adap);
-	sda = getsda(adap);
-	scl = (adap->getscl == NULL) ? 1 : getscl(adap);
-	if (!sda) {
-		printk(KERN_WARNING "%s: SDA stuck low!\n", name);
+	if (adap->getsda && !getsda(adap)) {
+		pr_warn("%s: SDA stuck low!\n", name);
 		goto bailout;
 	}
-	if (!scl) {
-		printk(KERN_WARNING
-		       "%s: SCL unexpected low while pulling SDA high!\n",
-		       name);
+	if (adap->getscl && !getscl(adap)) {
+		pr_warn("%s: SCL unexpected low while pulling SDA high!\n", name);
 		goto bailout;
 	}
 
 	scllo(adap);
-	sda = getsda(adap);
-	scl = (adap->getscl == NULL) ? 0 : getscl(adap);
-	if (scl) {
-		printk(KERN_WARNING "%s: SCL stuck high!\n", name);
+	if (adap->getscl && getscl(adap)) {
+		pr_warn("%s: SCL stuck high!\n", name);
 		goto bailout;
 	}
-	if (!sda) {
-		printk(KERN_WARNING
-		       "%s: SDA unexpected low while pulling SCL low!\n",
-		       name);
+	if (adap->getsda && !getsda(adap)) {
+		pr_warn("%s: SDA unexpected low while pulling SCL low!\n", name);
 		goto bailout;
 	}
 
 	sclhi(adap);
-	sda = getsda(adap);
-	scl = (adap->getscl == NULL) ? 1 : getscl(adap);
-	if (!scl) {
-		printk(KERN_WARNING "%s: SCL stuck low!\n", name);
+	if (adap->getscl && !getscl(adap)) {
+		pr_warn("%s: SCL stuck low!\n", name);
 		goto bailout;
 	}
-	if (!sda) {
-		printk(KERN_WARNING
-		       "%s: SDA unexpected low while pulling SCL high!\n",
-		       name);
+	if (adap->getsda && !getsda(adap)) {
+		pr_warn("%s: SDA unexpected low while pulling SCL high!\n", name);
 		goto bailout;
 	}
 
@@ -420,6 +405,10 @@ static int readbytes(struct i2c_adapter *i2c_adap, struct i2c_msg *msg)
 	unsigned char *temp = msg->buf;
 	int count = msg->len;
 	const unsigned flags = msg->flags;
+	struct i2c_algo_bit_data *adap = i2c_adap->algo_data;
+
+	if (!adap->getsda)
+		return -EOPNOTSUPP;
 
 	while (count > 0) {
 		inval = i2c_inb(i2c_adap);
@@ -670,11 +659,15 @@ static int __i2c_bit_add_bus(struct i2c_adapter *adap,
 	if (ret < 0)
 		return ret;
 
-	/* Complain if SCL can't be read */
-	if (bit_adap->getscl == NULL) {
+	if (bit_adap->getsda == NULL)
+		dev_warn(&adap->dev, "Not I2C compliant: can't read SDA\n");
+
+	if (bit_adap->getscl == NULL)
 		dev_warn(&adap->dev, "Not I2C compliant: can't read SCL\n");
+
+	if (bit_adap->getsda == NULL || bit_adap->getscl == NULL)
 		dev_warn(&adap->dev, "Bus may be unreliable\n");
-	}
+
 	return 0;
 }
 
-- 
2.39.0

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

[Heiner Kallweit]

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

Re: [PATCH v4 1/3] dt-bindings: i2c-gpio: Add properties for dealing with write-only SDA/SCL w/o pullup

[Rob Herring]

On Tue, Jan 17, 2023 at 09:36:05PM +0100, Heiner Kallweit wrote:
> 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.
> Therefore add properties for not using open-drain. For write-only SCL
> we have a property already, add one for write-only SDA.
> 
> Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
> ---
> v4:
> - add no-pullup properties
> ---
>  .../devicetree/bindings/i2c/i2c-gpio.yaml        | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/i2c/i2c-gpio.yaml b/Documentation/devicetree/bindings/i2c/i2c-gpio.yaml
> index e0d76d5eb..67898cc52 100644
> --- a/Documentation/devicetree/bindings/i2c/i2c-gpio.yaml
> +++ b/Documentation/devicetree/bindings/i2c/i2c-gpio.yaml
> @@ -33,6 +33,10 @@ properties:
>        open drain.
>      maxItems: 1
>  
> +  i2c-gpio,sda-output-only:
> +    description: sda as output only
> +    type: boolean
> +
>    i2c-gpio,scl-output-only:
>      description: scl as output only
>      type: boolean
> @@ -63,6 +67,18 @@ properties:
>        GPIO line used for SCL into open drain mode, and that something is not
>        the GPIO chip. It is essentially an inconsistency flag.
>  
> +  i2c-gpio,sda-has-no-pullup:
> +    type: boolean
> +    description: sda is used in a non-compliant way and has no pull-up.
> +      Therefore disable open-drain. This property is mutually-exclusive
> +      with i2c-gpio,sda-open-drain.
> +
> +  i2c-gpio,scl-has-no-pullup:
> +    type: boolean
> +    description: scl is used in a non-compliant way and has no pull-up.
> +      Therefore disable open-drain. This property is mutually-exclusive
> +      with i2c-gpio,scl-open-drain.

The mutual-exclusion can be expressed as a schema instead:

allOf:
  - not:
      required:
        - i2c-gpio,scl-has-no-pullup
        - i2c-gpio,scl-open-drain
  - not:
      required:
        - i2c-gpio,sda-has-no-pullup
        - i2c-gpio,sda-open-drain

Using 'dependencies' with a schema would also work.

Rob

Re: [PATCH v4 1/3] dt-bindings: i2c-gpio: Add properties for dealing with write-only SDA/SCL w/o pullup

[Heiner Kallweit]

On 18.01.2023 17:32, Rob Herring wrote:
> On Tue, Jan 17, 2023 at 09:36:05PM +0100, Heiner Kallweit wrote:
>> 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.
>> Therefore add properties for not using open-drain. For write-only SCL
>> we have a property already, add one for write-only SDA.
>>
>> Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
>> ---
>> v4:
>> - add no-pullup properties
>> ---
>>  .../devicetree/bindings/i2c/i2c-gpio.yaml        | 16 ++++++++++++++++
>>  1 file changed, 16 insertions(+)
>>
>> diff --git a/Documentation/devicetree/bindings/i2c/i2c-gpio.yaml b/Documentation/devicetree/bindings/i2c/i2c-gpio.yaml
>> index e0d76d5eb..67898cc52 100644
>> --- a/Documentation/devicetree/bindings/i2c/i2c-gpio.yaml
>> +++ b/Documentation/devicetree/bindings/i2c/i2c-gpio.yaml
>> @@ -33,6 +33,10 @@ properties:
>>        open drain.
>>      maxItems: 1
>>  
>> +  i2c-gpio,sda-output-only:
>> +    description: sda as output only
>> +    type: boolean
>> +
>>    i2c-gpio,scl-output-only:
>>      description: scl as output only
>>      type: boolean
>> @@ -63,6 +67,18 @@ properties:
>>        GPIO line used for SCL into open drain mode, and that something is not
>>        the GPIO chip. It is essentially an inconsistency flag.
>>  
>> +  i2c-gpio,sda-has-no-pullup:
>> +    type: boolean
>> +    description: sda is used in a non-compliant way and has no pull-up.
>> +      Therefore disable open-drain. This property is mutually-exclusive
>> +      with i2c-gpio,sda-open-drain.
>> +
>> +  i2c-gpio,scl-has-no-pullup:
>> +    type: boolean
>> +    description: scl is used in a non-compliant way and has no pull-up.
>> +      Therefore disable open-drain. This property is mutually-exclusive
>> +      with i2c-gpio,scl-open-drain.
> 
> The mutual-exclusion can be expressed as a schema instead:
> 
> allOf:
>   - not:
>       required:
>         - i2c-gpio,scl-has-no-pullup
>         - i2c-gpio,scl-open-drain
>   - not:
>       required:
>         - i2c-gpio,sda-has-no-pullup
>         - i2c-gpio,sda-open-drain
> 
> Using 'dependencies' with a schema would also work.
> 
Great, I wasn't aware of options to express mutually-exclusive properties.

I'll wait a little for other feedback regarding the series and then submit
a new version incl. the extended schema.

> Rob

Heiner