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Message-ID: <5491FC69.7090203@cogentembedded.com>
Date: Thu, 18 Dec 2014 00:58:01 +0300
From: Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To: Chanwoo Choi <cw00.choi@...sung.com>
CC: robh+dt@...nel.org, pawel.moll@....com, mark.rutland@....com,
ijc+devicetree@...lion.org.uk, galak@...eaurora.org,
myungjoo.ham@...sung.com, grant.likely@...aro.org,
devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-sh@...r.kernel.org, linux-usb@...r.kernel.org
Subject: Re: [PATCH] extcon: add MAX3355 driver
Hello.
On 12/17/2014 03:31 AM, Chanwoo Choi wrote:
>> MAX3355E chip integrates a charge pump and comparators to enable a system with
>> an integrated USB OTG dual-role transceiver to function as a USB OTG dual-role
>> device. In addition to sensing/controlling Vbus, the chip also passes thru the
>> ID signal from the USB OTG connector. On some Renesas boards, this signal is
>> just fed into the SoC thru a GPIO pin -- there's no real OTG controller, only
>> host and gadget USB controllers sharing the same USB bus; however, we'd like
>> to allow host or gadget drivers to be loaded depending on the cable type, hence
>> the need for the MAX3355 extcon driver. The Vbus status signals are also wired
>> to GPIOs (however, we're not currently intested in them), the OFFVBUS# signal
>> is controlled by the host controllers, there's also the SHDN# signal wired to
>> GPIO, which should be high for normal operation.
>> Signed-off-by: Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
>> ---
>> The patch is against the 'extcon-next' branch of the 'extcon.git' repo.
>> Documentation/devicetree/bindings/extcon/extcon-max3355.txt | 21 ++
>> drivers/extcon/Kconfig | 6
>> drivers/extcon/Makefile | 1
>> drivers/extcon/extcon-max3355.c | 122 ++++++++++++
>> 4 files changed, 150 insertions(+)
>> Index: extcon/Documentation/devicetree/bindings/extcon/extcon-max3355.txt
>> ===================================================================
>> --- /dev/null
>> +++ extcon/Documentation/devicetree/bindings/extcon/extcon-max3355.txt
>> @@ -0,0 +1,21 @@
>> +MAX3355 USB OTG chip
> Need manufactor information as following :
> -> Maxim MAX3355
Would be Maxim enough? Or perhaps I should use Maxim Integrated [Products]?
>> +--------------------
>> +
>> +MAX3355 integrates a charge pump and comparators to enable a system with an
>> +integrated USB OTG dual-role transceiver to function as a USB OTG dual-role
>> +device.
>> +
>> +Required properties:
>> +- compatible: should be "maxim,max3355";
>> +- maxim,shdn-gpio: should contain a phandle and GPIO specifier for the GPIO pin
>> + connected to the MAX3355's SHDN# pin;
>> +- maxim,id-gpio: should contain a phandle and GPIO specifier for the GPIO pin
>> + connected to the MAX3355's ID_OUT pin.
>> +
>> +Example (Koelsch board):
>> +
>> + usb-otg {
>> + compatible = "maxim,max3355";
>> + maxim,shdn-gpio = <&gpio2 4 GPIO_ACTIVE_LOW>;
>> + maxim,id-gpio = <&gpio5 31 GPIO_ACTIVE_HIGH>;
> Kernel already supported the gpio helper function to get gpio from devicetree.
> I prefer use follwoing style by using of_get_gpio()/of_get_gpio_flags() in include/linux/of_gpio.h.
> gpios = <&gpio2 4 GPIO_ACTIVE_LOW>, <&gpio5 31 GPIO_ACTIVE_HIGH>;
OK, though Documentation/devicetree/bindings/gpio/gpio.txt does not seem
to insist on using this one...
[...]
>> Index: extcon/drivers/extcon/extcon-max3355.c
>> ===================================================================
>> --- /dev/null
>> +++ extcon/drivers/extcon/extcon-max3355.c
>> @@ -0,0 +1,122 @@
>> +/*
>> + * MAX3355 USB OTG chip extcon driver
> ditto.
OK, though the other Maxim extcon drivers don't serve as a good example
here...
[...]
>> +static irqreturn_t max3355_id_irq(int irq, void *dev_id)
>> +{
>> + struct max3355_data *data = dev_id;
>> + int id = gpio_get_value(data->id_gpio);
>> +
>> + extcon_set_cable_state(data->edev, "USB-HOST", !id);
> You have to get the gpio flag in the devicetree by using of_get_gpio_flags() function
> and then you would set the cable state according to gpio state and flag.
I'm sorry but I just don't see why I have to do it. This is not a generic
GPIO driver, and the polarities of the GPIOs are determined solely by the
MAX3355 specs.
[...]
>> +static int max3355_probe(struct platform_device *pdev)
>> +{
>> + struct device_node *np = pdev->dev.of_node;
>> + struct max3355_data *data;
>> + int gpio, irq, ret;
>> +
>> + data = devm_kzalloc(&pdev->dev, sizeof(struct max3355_data),
>> + GFP_KERNEL);
>> + if (!data)
>> + return -ENOMEM;
>> +
>> + data->edev = devm_extcon_dev_allocate(&pdev->dev, max3355_cable);
>> + if (IS_ERR(data->edev)) {
>> + dev_err(&pdev->dev, "failed to allocate extcon device\n");
>> + return PTR_ERR(data->edev);
>> + }
>> + data->edev->name = kstrdup(np->name, GFP_KERNEL);
>> +
>> + gpio = of_get_named_gpio(np, "maxim,id-gpio", 0);
> Use of_get_gpio() or of_get_gpio_flags().
OK, I'll use the first one.
> "maxim,id-gpio" property has strong dependency on this driver and it is not standard.
I indented it to be Maxim specific. Not sure what using the standard
property buys...
>> + if (gpio < 0)
>> + return gpio;
> Need to add error message.
OK for all cases; extcon-gpio.c was probably a bad example...
[...]
>> +
>> + ret = devm_gpio_request_one(&pdev->dev, gpio, GPIOF_DIR_OUT |
>> + GPIOF_INIT_HIGH, pdev->name);
>> + if (ret < 0)
>> + return ret;
> Need to add error message.
>> +
>> + ret = devm_gpio_request_one(&pdev->dev, data->id_gpio, GPIOF_DIR_IN,
>> + pdev->name);
> Why do you use same name for two gpio when devm_gpio_request_one?
> I prefer to use other name because two gpio is different.
And you're absolutely right here. Mindlessly copy-pasted the code from
extcon-gpio.c...
[...]
>> +
>> + ret = devm_request_threaded_irq(&pdev->dev, irq, NULL, max3355_id_irq,
>> + IRQF_TRIGGER_RISING |
>> + IRQF_TRIGGER_FALLING | IRQF_ONESHOT,
> Is it right to add both RISING and FALLING trigger?
How else I'm supposed to know when the OTG ID signal goes low and high?
> and need to add IRQF_NO_SUSPEND to wakeup from suspend state when interrupt happen.
Hm, are you sure we want to wake up on plugging another kind of USB cable?
[...]
>> +static struct platform_driver max3355_driver = {
>> + .probe = max3355_probe,
>> + .driver = {
>> + .name = "extcon-max3355",
>> + .of_match_table = max3355_match_table,
>> + .owner = THIS_MODULE,
>> + },
>> +};
>> +
>> +module_platform_driver(max3355_driver);
>> +
> Don't need un-used blank line.
I don't understand. There's empty line in such case in extcon-gpio.c...
>> +MODULE_AUTHOR("Sergei Shtylyov <sergei.shtylyov@...entembedded.com>");
>> +MODULE_DESCRIPTION("MAX3355 extcon driver");
> Maxim MAX3355.
OK, seeing it in the other Maxim drivers.
>> +MODULE_LICENSE("GPL v2");
> Thanks,
> Chanwoo Choi
WBR, Sergei
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