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Message-ID: <54C7B0E5.20101@ti.com>
Date: Tue, 27 Jan 2015 17:38:13 +0200
From: Roger Quadros <rogerq@...com>
To: Chanwoo Choi <cw00.choi@...sung.com>
CC: Felipe Balbi <balbi@...com>, <tony@...mide.com>,
"myungjoo.ham@...sung.com" <myungjoo.ham@...sung.com>,
<george.cherian@...com>, <nsekhar@...com>,
devicetree <devicetree@...r.kernel.org>,
<linux-usb@...r.kernel.org>, <linux-omap@...r.kernel.org>,
linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/7] extcon: usb-gpio: Introduce gpio usb extcon driver
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@...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@...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
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