Date:   Mon, 19 Dec 2016 09:57:33 +0100
From:   Hans de Goede <hdegoede@...hat.com>
To:     Chanwoo Choi <cw00.choi@...sung.com>,
        MyungJoo Ham <myungjoo.ham@...sung.com>
Cc:     linux-kernel@...r.kernel.org, David Cohen <david.a.cohen@...el.com>
Subject: Re: [PATCH] extcon: 3gpio: add driver for USB OTG port controlled by
 3 GPIOs

Hi,

On 19-12-16 09:00, Chanwoo Choi wrote:
> Hi Hans,
>
> I'm glad to post new extcon driver. But, we need to discuss the device name of "3gpio".
>
> I think that "3 GPIO" is ambiguous. You need to find more proper name. For example, extcon-qcom-spmi-misc.c uses one interrupt line to detect "USB_HOST". This driver name means the "Qualcomm USB extcon support".

Ok, so this driver is for the INT3496 Intel ACPI device,
so I think we should put intel in the name, I see a 2 options:

1) extcon-intel-3gpio-otg.c
2) extcon-intel-INT3496.c

Which one do you like best ?


>
> Also, I recommend that you make the documentation for this driver.
>
> On 2016년 12월 19일 09:12, Hans de Goede wrote:
>> From: David Cohen <david.a.cohen@...el.com>
>>
>> Add an exntcon driver to for USB OTG ports controlled by 3 GPIOs used on
>> Intel Baytrail and Cherrytrail tablets.
>>
>> Signed-off-by: David Cohen <david.a.cohen@...el.com>
>> [hdgoede@...hat.com: Port to current kernel, submit upstream]
>> Signed-off-by: Hans de Goede <hdegoede@...hat.com>
>> ---
>>  drivers/extcon/Kconfig            |   7 ++
>>  drivers/extcon/Makefile           |   1 +
>>  drivers/extcon/extcon-3gpio_otg.c | 201 ++++++++++++++++++++++++++++++++++++++
>>  3 files changed, 209 insertions(+)
>>  create mode 100644 drivers/extcon/extcon-3gpio_otg.c
>>
>> diff --git a/drivers/extcon/Kconfig b/drivers/extcon/Kconfig
>> index 04788d9..1aaa64f 100644
>> --- a/drivers/extcon/Kconfig
>> +++ b/drivers/extcon/Kconfig
>> @@ -14,6 +14,13 @@ if EXTCON
>>
>>  comment "Extcon Device Drivers"
>>
>> +config EXTCON_3GPIO_OTG
>> +	tristate "3 GPIO USB OTG extcon driver"
>> +	depends on GPIOLIB || COMPILE_TEST
>> +	help
>> +	  Say Y here to enable extcon support for USB OTG ports controlled
>> +	  by 3 GPIOs used on Intel Baytrail and Cherrytrail tablets.
>> +
>>  config EXTCON_ADC_JACK
>>  	tristate "ADC Jack extcon support"
>>  	depends on IIO
>> diff --git a/drivers/extcon/Makefile b/drivers/extcon/Makefile
>> index 31a0a99..aa646fd 100644
>> --- a/drivers/extcon/Makefile
>> +++ b/drivers/extcon/Makefile
>> @@ -4,6 +4,7 @@
>>
>>  obj-$(CONFIG_EXTCON)		+= extcon-core.o
>>  extcon-core-objs		+= extcon.o devres.o
>> +obj-$(CONFIG_EXTCON_3GPIO_OTG)	+= extcon-3gpio_otg.o
>>  obj-$(CONFIG_EXTCON_ADC_JACK)	+= extcon-adc-jack.o
>>  obj-$(CONFIG_EXTCON_ARIZONA)	+= extcon-arizona.o
>>  obj-$(CONFIG_EXTCON_AXP288)	+= extcon-axp288.o
>> diff --git a/drivers/extcon/extcon-3gpio_otg.c b/drivers/extcon/extcon-3gpio_otg.c
>> new file mode 100644
>> index 0000000..fc8b14d1
>> --- /dev/null
>> +++ b/drivers/extcon/extcon-3gpio_otg.c
>> @@ -0,0 +1,201 @@
>> +/*
>> + * 3 GPIO USB OTG extcon driver
>> + *
>> + * Copyright (c) 2016) Hans de Goede <hdegoede@...hat.com>
>
> s/2016) -> 2016

Ok.

>
>> + *
>> + * Based on android x86 kernel code which is:
>> + *
>> + * Copyright (c) 2014, Intel Corporation.
>> + * Author: David Cohen <david.a.cohen@...ux.intel.com>
>> + *
>> + * This program is free software; you can redistribute it and/or modify
>> + * it under the terms of the GNU General Public License version 2 as
>> + * published by the Free Software Foundation.
>> + *
>> + * This program is distributed in the hope that it will be useful,
>> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
>> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
>> + * GNU General Public License for more details.
>> + */
>> +
>> +#include <linux/acpi.h>
>> +#include <linux/extcon.h>
>> +#include <linux/gpio.h>
>> +#include <linux/interrupt.h>
>> +#include <linux/platform_device.h>
>> +
>> +#define DRV_NAME		"usb_otg_port"
>
> This definition is not necessary. It is used only one time in this driver. Also, this name should reflect specific hardware.

Ok.

>> +#define USB_OTG_GPIO_USB_ID	0
>> +#define USB_OTG_GPIO_VBUS_EN	1
>> +#define USB_OTG_GPIO_USB_MUX	2
>> +#define DEBOUNCE_TIME		msecs_to_jiffies(50)
>
> I recommend that you use the gpiod_set_debounce() to get the debounce time. If there is any property for debounce, you use the default debounce time of DEBOUNCE_TIME.

This driver is for Intel SoCs only, and Intel SoC's gpios
do not support gpiod_set_debounce(), so calling it only
to find out it returns -ENOTSUPP and then still doing
debounce ourselves does not seem useful.

>> +
>> +struct usb_otg {
>> +	struct device *dev;
>> +	struct extcon_dev *edev;
>> +	struct delayed_work work;
>> +	struct gpio_desc *gpio_usb_id;
>> +	struct gpio_desc *gpio_vbus_en;
>> +	struct gpio_desc *gpio_usb_mux;
>> +	int usb_id_irq;
>> +};
>> +
>> +static const unsigned int usb_otg_cable[] = {
>> +	EXTCON_USB_HOST,
>> +	EXTCON_NONE,
>> +};
>> +
>> +/*
>> + * If id == 1, USB port should be set to peripheral
>> + * if id == 0, USB port should be set to host
>> + *
>> + * Peripheral: set USB mux to peripheral and disable VBUS
>> + * Host: set USB mux to host and enable VBUS
>> + */
>> +static void usb_otg_set_port(struct usb_otg *otg, int id)
>> +{
>> +	int mux_val = id;
>> +	int vbus_val = !id;
>> +
>> +	if (!IS_ERR(otg->gpio_usb_mux))
>> +		gpiod_direction_output(otg->gpio_usb_mux, mux_val);
>> +
>> +	if (!IS_ERR(otg->gpio_vbus_en))
>> +		gpiod_direction_output(otg->gpio_vbus_en, vbus_val);
>> +}
>> +
>> +static void usb_otg_do_usb_id(struct work_struct *work)
>> +{
>> +	struct usb_otg *otg =
>> +		container_of(work, struct usb_otg, work.work);
>> +	int id = gpiod_get_value_cansleep(otg->gpio_usb_id);
>> +
>> +	dev_info(otg->dev, "USB PORT ID: %s\n", id ? "PERIPHERAL" : "HOST");
>
> I don't prefer to use the dev_info() on the fly. And I recommend that you modify the debug message which include more correct information.
>
> 	It is just example. Not forced.
> 	dev_dbg(otg->dev, "Connected device is %s\n", id ? "PERIPHERAL" : "HOST");

Ok.

>> +
>> +	/*
>> +	 * id == 1: PERIPHERAL
>> +	 * id == 0: HOST
>> +	 */
>> +	usb_otg_set_port(otg, id);
>
> This function is used only one time in this driver and it is not complex. You don't need to make the separate function.

Ok.

>> +
>> +	/*
>> +	 * id == 0: HOST connected
>> +	 * id == 1: Host disconnected
>> +	 */
>> +	extcon_set_state_sync(otg->edev, EXTCON_USB_HOST, !id);
>> +}
>> +
>> +static irqreturn_t usb_otg_thread_isr(int irq, void *priv)
>> +{
>> +	struct usb_otg *otg = priv;
>> +
>> +	/* id changed, let the pin settle and then process it */
>
> I think "id changed" comment is unneeded.

The comment is there because of the "let the pin settle" bit,
it explains why DEBOUNCE_TIME is used.

>> +	mod_delayed_work(system_wq, &otg->work, DEBOUNCE_TIME);
>> +
>> +	return IRQ_HANDLED;
>> +}
>> +
>> +static int usb_otg_probe(struct platform_device *pdev)
>> +{
>> +	struct device *dev = &pdev->dev;
>> +	struct usb_otg *otg;
>> +	int ret;
>> +
>> +	otg = devm_kzalloc(dev, sizeof(*otg), GFP_KERNEL);
>> +	if (!otg)
>> +		return -ENOMEM;
>> +
>> +	otg->dev = dev;
>> +	INIT_DELAYED_WORK(&otg->work, usb_otg_do_usb_id);
>> +
>> +	otg->gpio_usb_id = devm_gpiod_get_index(dev, "id",
>> +						USB_OTG_GPIO_USB_ID,
>> +						GPIOD_IN);
>> +	if (IS_ERR(otg->gpio_usb_id)) {
>> +		dev_err(dev, "can't request USB ID GPIO: ret = %ld\n",
>> +			PTR_ERR(otg->gpio_usb_id));
>> +		return PTR_ERR(otg->gpio_usb_id);
>
> I prefer to use the consistent error message. This patch uses two style sentence when error happen as following: I recommend that you use the one style.
> - "can't ..."
> - "failed to ..."
>
> how about changing the print style of error message as following? Because other error message print just error value in this driver.
> - ": ret = %ld" -> ": %d"

Ok, will fix.

>
>> +	}
>> +
>> +	otg->usb_id_irq = gpiod_to_irq(otg->gpio_usb_id);
>> +	if (otg->usb_id_irq <= 0) {
>> +		dev_err(dev, "invalid USB ID IRQ: %d\n", otg->usb_id_irq);
>
> ditto.
>
>> +		return -EINVAL;
>> +	}
>> +
>> +	otg->gpio_vbus_en = devm_gpiod_get_index(dev, "vbus en",
>> +						 USB_OTG_GPIO_VBUS_EN,
>> +						 GPIOD_ASIS);
>> +	if (IS_ERR(otg->gpio_vbus_en))
>> +		dev_info(dev, "can't request VBUS EN GPIO, skipping it.\n");
>
> I think that "skipping it." is unneeded.

Ok.

>> +
>> +	otg->gpio_usb_mux = devm_gpiod_get_index(dev, "usb mux",
>> +						 USB_OTG_GPIO_USB_MUX,
>> +						 GPIOD_ASIS);
>> +	if (IS_ERR(otg->gpio_usb_mux))
>> +		dev_info(dev, "can't request USB MUX, skipping it.\n");
>
> I think that "skipping it." is unneeded.
>
>> +
>> +	/* register extcon device */
>> +	otg->edev = devm_extcon_dev_allocate(dev, usb_otg_cable);
>> +	if (IS_ERR(otg->edev)) {
>> +		dev_err(dev, "failed to allocate extcon device\n");
>
> ditto.
>
>> +		return -ENOMEM;
>> +	}
>> +
>> +	ret = devm_extcon_dev_register(dev, otg->edev);
>> +	if (ret < 0) {
>> +		dev_err(dev, "failed to register extcon device: %d\n",
>> +			ret);
>
> ditto.
>
>> +		return ret;
>> +	}
>> +
>> +	ret = devm_request_threaded_irq(dev, otg->usb_id_irq,
>> +					NULL, usb_otg_thread_isr,
>> +					IRQF_SHARED | IRQF_ONESHOT |
>> +					IRQF_TRIGGER_RISING |
>> +					IRQF_TRIGGER_FALLING,
>> +					dev_name(dev), otg);
>> +	if (ret < 0) {
>> +		dev_err(dev, "can't request IRQ for USB ID GPIO: %d\n", ret);
>
> ditto.
>
>> +		return ret;
>> +	}
>> +
>> +	/* queue initial processing of id-pin */
>> +	queue_delayed_work(system_wq, &otg->work, 0);
>> +
>> +	platform_set_drvdata(pdev, otg);
>> +
>> +	return 0;
>> +}
>> +
>> +static int usb_otg_remove(struct platform_device *pdev)
>> +{
>> +	struct usb_otg *otg = platform_get_drvdata(pdev);
>> +
>> +	devm_free_irq(&pdev->dev, otg->usb_id_irq, otg);
>
> As I knew, you don't need to free irq when using devm_request_threaded_irq() function.

Correct, but we need to free it before cancelling the work, otherwise
the irq may trigger between us cancelling the work and the devm code
disabling the irq, re-queueing the work while the struct work
now sits in free-ed memory and bad things happen.

>> +	cancel_delayed_work_sync(&otg->work);
>> +
>> +	return 0;
>> +}
>> +
>> +static struct acpi_device_id usb_otg_acpi_match[] = {
>> +	{ "INT3496" },
>
> What is meaning of "INT3496"?

It is the ACPI hardware-id for the ACPI device representing
the presence of an otg connector which should be handled by
this driver. The INT stands for Intel, the rest is just like
say a pci device-id, so a vendor defined number.

>
>> +	{ }
>> +};
>> +MODULE_DEVICE_TABLE(acpi, usb_otg_acpi_match);
>> +
>> +static struct platform_driver usb_otg_driver = {
>> +	.driver = {
>> +		.name = DRV_NAME,
>
> ditto. You can set the driver name directly without separate definition.

Ok.

>> +		.owner = THIS_MODULE,
>> +		.acpi_match_table = ACPI_PTR(usb_otg_acpi_match),
>> +	},
>> +	.probe = usb_otg_probe,
>> +	.remove = usb_otg_remove,
>> +};
>> +
>> +module_platform_driver(usb_otg_driver);
>> +
>> +MODULE_AUTHOR("Hans de Goede <hdegoede@...hat.com>");
>> +MODULE_DESCRIPTION("3 GPIO USB OTG extcon driver");
>> +MODULE_LICENSE("GPL");
>>
>


Thank you for the review, I will send a v2 when we've decided on a better
name for the driver.

Regards,

Hans

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