Re: [PATCH v2 1/7] extcon: usb-gpio: Introduce gpio usb extcon driver

[Roger Quadros <rogerq@ti.com>]

Chanwoo,

On 27/01/15 03:54, Chanwoo Choi wrote:
> Hi Roger,
> 
> On 01/27/2015 01:27 AM, Roger Quadros wrote:
>> Hi Chanwoo,
>>
>> All your comments are valid. Need some clarification on one comment.
>>
>> On 26/01/15 15:56, Chanwoo Choi wrote:
>>> Hi Roger,
>>>
>>> This patch looks good to me. But I add some comment.
>>> If you modify some comment, I'll apply this patch on 3.21 queue.
>>>
>>> On Mon, Jan 26, 2015 at 9:15 PM, Roger Quadros <rogerq@ti.com> wrote:
>>>> This driver observes the USB ID pin connected over a GPIO and
>>>> updates the USB cable extcon states accordingly.
>>>>
>>>> The existing GPIO extcon driver is not suitable for this purpose
>>>> as it needs to be taught to understand USB cable states and it
>>>> can't handle more than one cable per instance.
>>>>
>>>> For the USB case we need to handle 2 cable states.
>>>> 1) USB (attach/detach)
>>>> 2) USB-Host (attach/detach)
>>>>
>>>> This driver can be easily updated in the future to handle VBUS
>>>> events in case it happens to be available on GPIO for any platform.
>>>>
>>>> Signed-off-by: Roger Quadros <rogerq@ti.com>
>>>> ---
>>>>  .../devicetree/bindings/extcon/extcon-usb-gpio.txt |  20 ++
>>>>  drivers/extcon/Kconfig                             |   7 +
>>>>  drivers/extcon/Makefile                            |   1 +
>>>>  drivers/extcon/extcon-usb-gpio.c                   | 214 +++++++++++++++++++++
>>>>  4 files changed, 242 insertions(+)
>>>>  create mode 100644 Documentation/devicetree/bindings/extcon/extcon-usb-gpio.txt
>>>>  create mode 100644 drivers/extcon/extcon-usb-gpio.c
>>>>
>>
>> <snip>
>>
>>>> +
>>>> +static int usb_extcon_probe(struct platform_device *pdev)
>>>> +{
>>>> +       struct device *dev = &pdev->dev;
>>>> +       struct device_node *np = dev->of_node;
>>>> +       struct usb_extcon_info *info;
>>>> +       int ret;
>>>> +
>>>> +       if (!np)
>>>> +               return -EINVAL;
>>>> +
>>>> +       info = devm_kzalloc(&pdev->dev, sizeof(*info), GFP_KERNEL);
>>>> +       if (!info)
>>>> +               return -ENOMEM;
>>>> +
>>>> +       info->dev = dev;
>>>> +       info->id_gpiod = devm_gpiod_get(&pdev->dev, "id");
>>>> +       if (IS_ERR(info->id_gpiod)) {
>>>> +               dev_err(dev, "failed to get ID GPIO\n");
>>>> +               return PTR_ERR(info->id_gpiod);
>>>> +       }
>>>> +
>>>> +       ret = gpiod_set_debounce(info->id_gpiod,
>>>> +                                USB_GPIO_DEBOUNCE_MS * 1000);
>>>> +       if (ret < 0)
>>>> +               info->debounce_jiffies = msecs_to_jiffies(USB_GPIO_DEBOUNCE_MS);
>>>> +
>>>> +       INIT_DELAYED_WORK(&info->wq_detcable, usb_extcon_detect_cable);
>>>> +
>>>> +       info->id_irq = gpiod_to_irq(info->id_gpiod);
>>>> +       if (info->id_irq < 0) {
>>>> +               dev_err(dev, "failed to get ID IRQ\n");
>>>> +               return info->id_irq;
>>>> +       }
>>>> +
>>>> +       ret = devm_request_threaded_irq(dev, info->id_irq, NULL,
>>>> +                                       usb_irq_handler,
>>>> +                                       IRQF_SHARED | IRQF_ONESHOT |
>>>> +                                       IRQF_NO_SUSPEND,
>>>> +                                       pdev->name, info);
>>
>> use of IRQF_NO_SUSPEND is not recommended to be used together with IRQF_SHARED so
>> I'll remove IRQF_SHARED from here if we decide to stick with IRQF_NO_SUSPEND.
>> More on this below.
>>
>>>> +       if (ret < 0) {
>>>> +               dev_err(dev, "failed to request handler for ID IRQ\n");
>>>> +               return ret;
>>>> +       }
>>>> +
>>>> +       info->edev = devm_extcon_dev_allocate(dev, usb_extcon_cable);
>>>> +       if (IS_ERR(info->edev)) {
>>>> +               dev_err(dev, "failed to allocate extcon device\n");
>>>> +               return -ENOMEM;
>>>> +       }
>>>> +
>>>> +       ret = devm_extcon_dev_register(dev, info->edev);
>>>> +       if (ret < 0) {
>>>> +               dev_err(dev, "failed to register extcon device\n");
>>>> +               return ret;
>>>> +       }
>>>> +
>>>> +       platform_set_drvdata(pdev, info);
>>>
>>> I prefer to execute the device_init_wakeup() function as following
>>> for suspend/resume function:
>>>             device_init_wakeup(&pdev->dev, 1);
>>>
>>>> +
>>>> +       /* Perform initial detection */
>>>> +       usb_extcon_detect_cable(&info->wq_detcable.work);
>>>> +
>>>> +       return 0;
>>>> +}
>>>> +
>>>> +static int usb_extcon_remove(struct platform_device *pdev)
>>>> +{
>>>> +       struct usb_extcon_info *info = platform_get_drvdata(pdev);
>>>> +
>>>> +       cancel_delayed_work_sync(&info->wq_detcable);
>>>
>>> Need to add blank line.
>>>
>>>> +       return 0;
>>>> +}
>>>> +
>>>> +#ifdef CONFIG_PM_SLEEP
>>>> +static int usb_extcon_suspend(struct device *dev)
>>>> +{
>>>> +       struct usb_extcon_info *info = dev_get_drvdata(dev);
>>>> +
>>>> +       enable_irq_wake(info->id_irq);
>>>
>>> I prefer to use device_may_wakeup() function for whether
>>> executing enable_irq_wake() or not. Also, The disable_irq()
>>> in the suspend function would prevent us from discarding interrupt
>>> before wakeup from suspend completely.
>>>
>>
>> I need more clarification here.
>>
>> If we are going to use enable_irq_wake() here then what is the point of IRQF_NO_SUSPEND?
>>
>> >From Documentation/power/suspend-and-interrupts.txt I see that interrupts marked
>> as IRQF_NO_SUSPEND should not be configured for system wakeup using enable_irq_wake().
>>
>> what is your preference?
>>
>> Is it good enough to not use IRQF_NO_SUSPEND but use enable_irq_wake() instead to
>> enable system wakeup for that IRQ.
> 
> I'm sorry for confusion about usage both IRQF_NO_SUSPEND and enable_irq_wake().
> If suspend() function in device driver executes the enable_irq_wake(),
> IRQF_NO_SUSPEND flag is not necessary.
> 
> I think that we better use enable_irq_wake() instead of adding IRQF_NO_SUSPEND flag.
> I'll expect to remove IRQF_NO_SUSPEND flag when requesting gpio interrupt.
> 
OK.

>>
>>>             if (device_may_wakeup(dev))
>>>                      enable_irq_wake(info->id_irq);
>>>             disable_irq(info->id_irq);
>>
>> why do we need to disable irq here? How will the system wakeup if IRQ is disabled?
> 
> The disable_irq() may make the interrupt as masking state.
> Although interrput is masking state(disable), interrup can happen.
> but, the interrupt may remain the pending state without discarding it.
> 
> And then,
> When resume() function in extcon-usb-gpio.c executes enable_irq(info->id_irq),
> pending interrupt will happen and executes the interrupt handler(usb_irq_handler).
> 
> If we don't execute disable_irq() in suspend function,
> info->id->irq interrupt might happen before completing the resume sequence
> of extcon-gpio-usb driver.

How will that cause a problem? If an interrupt happens _before_ the system enters
SUSPEND state then kernel should abort the suspend. This should be taken care by 
kernel PM core and not the device driver.

I still fail to understand that we need to call disable_irq() in .suspend() and
enable_irq() in .resume()

can you point me to any other drivers doing so?

cheers,
-roger