[PATCH v2 0/2] usb: usb251xb: support usage case without I2C control

[PATCH v2 0/2] usb: usb251xb: support usage case without I2C control

[Jisheng Zhang]

Refactor so that register writes for configuration are only performed if
the device has a i2c_client provided and also register as a platform
driver. This allows the driver to be used to manage GPIO based control
of the device.

Since v1:
 - make the modern pm macros usage a separate patch
 - use pm_sleep_ptr instead of pm_ptr for usb251xb_plat_pm_ops, because
   this ops is for PM_SLEEP only.

Jisheng Zhang (3):
  dt-bindings: usb: usb251xb: make reg optional for no I2C ctrl use case
  usb: usb251xb: use modern PM macros
  usb: usb251xb: support usage case without I2C control

 .../devicetree/bindings/usb/usb251xb.yaml     |   1 -
 drivers/usb/misc/usb251xb.c                   | 108 +++++++++++++++---
 2 files changed, 94 insertions(+), 15 deletions(-)

-- 
2.50.0

[PATCH v2 1/3] dt-bindings: usb: usb251xb: make reg optional for no I2C ctrl use case

[Jisheng Zhang]

Make "reg" optional to allow the driver to be used to manage GPIO
based control of the device.

Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
---
 Documentation/devicetree/bindings/usb/usb251xb.yaml | 1 -
 1 file changed, 1 deletion(-)

diff --git a/Documentation/devicetree/bindings/usb/usb251xb.yaml b/Documentation/devicetree/bindings/usb/usb251xb.yaml
index ac5b99710332..4b676c010f3e 100644
--- a/Documentation/devicetree/bindings/usb/usb251xb.yaml
+++ b/Documentation/devicetree/bindings/usb/usb251xb.yaml
@@ -240,7 +240,6 @@ additionalProperties: false
 
 required:
   - compatible
-  - reg
 
 examples:
   - |
-- 
2.50.0

Re: [PATCH v2 1/3] dt-bindings: usb: usb251xb: make reg optional for no I2C ctrl use case

[Krzysztof Kozlowski]

On Tue, Aug 19, 2025 at 08:22:15AM +0800, Jisheng Zhang wrote:
> Make "reg" optional to allow the driver to be used to manage GPIO
> based control of the device.

I don't understand how optional reg allows or disallows anything for the
driver. It's really not relevant to GPIO at all.

Also feels wrong, but maybe you just lack proper, reasonable
justification. Just explain carefully the hardware, not drivers.

Best regards,
Krzysztof

Re: [PATCH v2 1/3] dt-bindings: usb: usb251xb: make reg optional for no I2C ctrl use case

[Jisheng Zhang]

On Tue, Aug 19, 2025 at 11:22:51AM +0200, Krzysztof Kozlowski wrote:
> On Tue, Aug 19, 2025 at 08:22:15AM +0800, Jisheng Zhang wrote:
> > Make "reg" optional to allow the driver to be used to manage GPIO
> > based control of the device.
> 
> I don't understand how optional reg allows or disallows anything for the
> driver. It's really not relevant to GPIO at all.

w/o this patch, then there will be DT check complains for the following
usb251xb usage:

usb-hub {
	compatible = "microchip,usb2512b";
	reset-gpios = <&porta 2 GPIO_ACTIVE_LOW>;
};


> 
> Also feels wrong, but maybe you just lack proper, reasonable
> justification. Just explain carefully the hardware, not drivers.

It's simple, the hub allows usage w/o connecting to any i2c, see above
example for reference. But current dt-binding make the reg required.

Regards.

[PATCH v2 2/3] usb: usb251xb: use modern PM macros

[Jisheng Zhang]

Use the modern PM macros for the suspend and resume functions to be
automatically dropped by the compiler when CONFIG_PM or
CONFIG_PM_SLEEP are disabled, without having to use __maybe_unused.

Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
---
 drivers/usb/misc/usb251xb.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/usb/misc/usb251xb.c b/drivers/usb/misc/usb251xb.c
index 4fb453ca5450..cb2f946de42c 100644
--- a/drivers/usb/misc/usb251xb.c
+++ b/drivers/usb/misc/usb251xb.c
@@ -698,7 +698,7 @@ static int usb251xb_i2c_probe(struct i2c_client *i2c)
 	return usb251xb_probe(hub);
 }
 
-static int __maybe_unused usb251xb_suspend(struct device *dev)
+static int usb251xb_suspend(struct device *dev)
 {
 	struct i2c_client *client = to_i2c_client(dev);
 	struct usb251xb *hub = i2c_get_clientdata(client);
@@ -706,7 +706,7 @@ static int __maybe_unused usb251xb_suspend(struct device *dev)
 	return regulator_disable(hub->vdd);
 }
 
-static int __maybe_unused usb251xb_resume(struct device *dev)
+static int usb251xb_resume(struct device *dev)
 {
 	struct i2c_client *client = to_i2c_client(dev);
 	struct usb251xb *hub = i2c_get_clientdata(client);
@@ -719,7 +719,7 @@ static int __maybe_unused usb251xb_resume(struct device *dev)
 	return usb251xb_connect(hub);
 }
 
-static SIMPLE_DEV_PM_OPS(usb251xb_pm_ops, usb251xb_suspend, usb251xb_resume);
+static DEFINE_SIMPLE_DEV_PM_OPS(usb251xb_pm_ops, usb251xb_suspend, usb251xb_resume);
 
 static const struct i2c_device_id usb251xb_id[] = {
 	{ "usb2422" },
@@ -739,7 +739,7 @@ static struct i2c_driver usb251xb_i2c_driver = {
 	.driver = {
 		.name = DRIVER_NAME,
 		.of_match_table = usb251xb_of_match,
-		.pm = &usb251xb_pm_ops,
+		.pm = pm_sleep_ptr(&usb251xb_pm_ops),
 	},
 	.probe = usb251xb_i2c_probe,
 	.id_table = usb251xb_id,
-- 
2.50.0

[PATCH v2 3/3] usb: usb251xb: support usage case without I2C control

[Jisheng Zhang]

Refactor so that register writes for configuration are only performed if
the device has a i2c_client provided and also register as a platform
driver. This allows the driver to be used to manage GPIO based control
of the device.

Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
---
 drivers/usb/misc/usb251xb.c | 108 +++++++++++++++++++++++++++++++-----
 1 file changed, 94 insertions(+), 14 deletions(-)

diff --git a/drivers/usb/misc/usb251xb.c b/drivers/usb/misc/usb251xb.c
index cb2f946de42c..c900df69dd8d 100644
--- a/drivers/usb/misc/usb251xb.c
+++ b/drivers/usb/misc/usb251xb.c
@@ -17,6 +17,7 @@
 #include <linux/module.h>
 #include <linux/nls.h>
 #include <linux/of.h>
+#include <linux/platform_device.h>
 #include <linux/regulator/consumer.h>
 #include <linux/slab.h>
 
@@ -242,15 +243,19 @@ static int usb251xb_check_dev_children(struct device *dev, void *child)
 static int usb251x_check_gpio_chip(struct usb251xb *hub)
 {
 	struct gpio_chip *gc = gpiod_to_chip(hub->gpio_reset);
-	struct i2c_adapter *adap = hub->i2c->adapter;
+	struct i2c_adapter *adap;
 	int ret;
 
+	if (!hub->i2c)
+		return 0;
+
 	if (!hub->gpio_reset)
 		return 0;
 
 	if (!gc)
 		return -EINVAL;
 
+	adap = hub->i2c->adapter;
 	ret = usb251xb_check_dev_children(&adap->dev, gc->parent);
 	if (ret) {
 		dev_err(hub->dev, "Reset GPIO chip is at the same i2c-bus\n");
@@ -271,7 +276,8 @@ static void usb251xb_reset(struct usb251xb *hub)
 	if (!hub->gpio_reset)
 		return;
 
-	i2c_lock_bus(hub->i2c->adapter, I2C_LOCK_SEGMENT);
+	if (hub->i2c)
+		i2c_lock_bus(hub->i2c->adapter, I2C_LOCK_SEGMENT);
 
 	gpiod_set_value_cansleep(hub->gpio_reset, 1);
 	usleep_range(1, 10);	/* >=1us RESET_N asserted */
@@ -280,7 +286,8 @@ static void usb251xb_reset(struct usb251xb *hub)
 	/* wait for hub recovery/stabilization */
 	usleep_range(500, 750);	/* >=500us after RESET_N deasserted */
 
-	i2c_unlock_bus(hub->i2c->adapter, I2C_LOCK_SEGMENT);
+	if (hub->i2c)
+		i2c_unlock_bus(hub->i2c->adapter, I2C_LOCK_SEGMENT);
 }
 
 static int usb251xb_connect(struct usb251xb *hub)
@@ -289,7 +296,11 @@ static int usb251xb_connect(struct usb251xb *hub)
 	int err, i;
 	char i2c_wb[USB251XB_I2C_REG_SZ];
 
-	memset(i2c_wb, 0, USB251XB_I2C_REG_SZ);
+	if (!hub->i2c) {
+		usb251xb_reset(hub);
+		dev_info(dev, "hub is put in default configuration.\n");
+		return 0;
+	}
 
 	if (hub->skip_config) {
 		dev_info(dev, "Skip hub configuration, only attach.\n");
@@ -698,18 +709,13 @@ static int usb251xb_i2c_probe(struct i2c_client *i2c)
 	return usb251xb_probe(hub);
 }
 
-static int usb251xb_suspend(struct device *dev)
+static int usb251xb_suspend(struct usb251xb *hub)
 {
-	struct i2c_client *client = to_i2c_client(dev);
-	struct usb251xb *hub = i2c_get_clientdata(client);
-
 	return regulator_disable(hub->vdd);
 }
 
-static int usb251xb_resume(struct device *dev)
+static int usb251xb_resume(struct usb251xb *hub)
 {
-	struct i2c_client *client = to_i2c_client(dev);
-	struct usb251xb *hub = i2c_get_clientdata(client);
 	int err;
 
 	err = regulator_enable(hub->vdd);
@@ -719,7 +725,23 @@ static int usb251xb_resume(struct device *dev)
 	return usb251xb_connect(hub);
 }
 
-static DEFINE_SIMPLE_DEV_PM_OPS(usb251xb_pm_ops, usb251xb_suspend, usb251xb_resume);
+static int usb251xb_i2c_suspend(struct device *dev)
+{
+	struct i2c_client *client = to_i2c_client(dev);
+	struct usb251xb *hub = i2c_get_clientdata(client);
+
+	return usb251xb_suspend(hub);
+}
+
+static int usb251xb_i2c_resume(struct device *dev)
+{
+	struct i2c_client *client = to_i2c_client(dev);
+	struct usb251xb *hub = i2c_get_clientdata(client);
+
+	return usb251xb_resume(hub);
+}
+
+static DEFINE_SIMPLE_DEV_PM_OPS(usb251xb_i2c_pm_ops, usb251xb_i2c_suspend, usb251xb_i2c_resume);
 
 static const struct i2c_device_id usb251xb_id[] = {
 	{ "usb2422" },
@@ -739,13 +761,71 @@ static struct i2c_driver usb251xb_i2c_driver = {
 	.driver = {
 		.name = DRIVER_NAME,
 		.of_match_table = usb251xb_of_match,
-		.pm = pm_sleep_ptr(&usb251xb_pm_ops),
+		.pm = pm_sleep_ptr(&usb251xb_i2c_pm_ops),
 	},
 	.probe = usb251xb_i2c_probe,
 	.id_table = usb251xb_id,
 };
 
-module_i2c_driver(usb251xb_i2c_driver);
+static int usb251xb_plat_probe(struct platform_device *pdev)
+{
+	struct usb251xb *hub;
+
+	hub = devm_kzalloc(&pdev->dev, sizeof(*hub), GFP_KERNEL);
+	if (!hub)
+		return -ENOMEM;
+
+	platform_set_drvdata(pdev, hub);
+	hub->dev = &pdev->dev;
+
+	return usb251xb_probe(hub);
+}
+
+static int usb251xb_plat_suspend(struct device *dev)
+{
+	return usb251xb_suspend(dev_get_drvdata(dev));
+}
+
+static int usb251xb_plat_resume(struct device *dev)
+{
+	return usb251xb_resume(dev_get_drvdata(dev));
+}
+
+static DEFINE_SIMPLE_DEV_PM_OPS(usb251xb_plat_pm_ops, usb251xb_plat_suspend, usb251xb_plat_resume);
+
+static struct platform_driver usb251xb_plat_driver = {
+	.driver = {
+		.name = DRIVER_NAME,
+		.of_match_table = of_match_ptr(usb251xb_of_match),
+		.pm = pm_sleep_ptr(&usb251xb_plat_pm_ops),
+	},
+	.probe		= usb251xb_plat_probe,
+};
+
+static int __init usb251xb_init(void)
+{
+	int err;
+
+	err = i2c_add_driver(&usb251xb_i2c_driver);
+	if (err)
+		return err;
+
+	err = platform_driver_register(&usb251xb_plat_driver);
+	if (err) {
+		i2c_del_driver(&usb251xb_i2c_driver);
+		return err;
+	}
+
+	return 0;
+}
+module_init(usb251xb_init);
+
+static void __exit usb251xb_exit(void)
+{
+	platform_driver_unregister(&usb251xb_plat_driver);
+	i2c_del_driver(&usb251xb_i2c_driver);
+}
+module_exit(usb251xb_exit);
 
 MODULE_AUTHOR("Richard Leitner <richard.leitner@skidata.com>");
 MODULE_DESCRIPTION("USB251x/xBi USB 2.0 Hub Controller Driver");
-- 
2.50.0

Re: [PATCH v2 3/3] usb: usb251xb: support usage case without I2C control

[Krzysztof Kozlowski]

On Tue, Aug 19, 2025 at 08:22:17AM +0800, Jisheng Zhang wrote:
> +
> +static DEFINE_SIMPLE_DEV_PM_OPS(usb251xb_plat_pm_ops, usb251xb_plat_suspend, usb251xb_plat_resume);
> +
> +static struct platform_driver usb251xb_plat_driver = {
> +	.driver = {
> +		.name = DRIVER_NAME,
> +		.of_match_table = of_match_ptr(usb251xb_of_match),

No, drop of_match_ptr. This is neither correct nor helpful.
Look at existing code.

Best regards,
Krzysztof