linux-kernel - Re: [PATCH] extcon: add MAX3355 driver

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Date:	Tue, 10 Nov 2015 14:03:21 +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 11/10/2015 2:52 AM, Chanwoo Choi wrote:

> I received the reply from you after too long time (17~18day).
> You better to reply it more a little more quickly
> if you have the question or new patches.

    I've replied as soon as I had my new idea.

>>>>>>> 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]?
>>>>
>>>>      You haven't replied to my questions.
>>>>
>>>>>>> +--------------------
>>>>>>> +
>>>>>>> +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...
>>>>
>>>>      Moreover, it now says "gpios" isn't allowed for the new bindings. So I have to strongly disagree here...
>>>
>>> OK. But, I recommend you use the 'gpiod' with devm_gpiod_get
>>> instead of using devm_gpio_request_one() directly as following:
>>> You can refer drivers/extcon/extcon-usb-gpio.c about using gpiod.
>>>
>>> For example,
>>>      data->shdn_gpiod = devm_gpiod_get(dev, "maxim,shdn", GPIOD_IN);
>>>      data->id_gpiod = devm_gpiod_get(dev, "maxim,id", GPIOD_IN);
>>
>>     Thanks, done now. I just had another idea: how about I add an optional "enable-gpio" property to the 'extcon-usb-gpio' driver? I wouldn't need my own driver then at all... :-)
>
> What is meaning of 'enable-gpio' property?
> You better to explain your goal about 'enable-gpio' property

    This optional property would serve for enabling the valid signal on the ID 
GPIO, the same way I'm using the SHDN# GPIO in the MAX3355 driver.

> Also, If you think that it is generic way about
> adding 'enable-gpio' property to extcon-usb-gpio.c,
> you can try it.

    Yes, I think it would be generic enough.

> Thanks,
> Chanwoo Choi

MBR, Sergei

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