linux-kernel - Re: [PATCH v3 3/3] gpio: add support for Cypress CYUSBS234 USB-GPIO adapter

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Message-ID: <CACdXCX7PqUHRKJ0KipmYzRF54XRmMYYArr5iof36VskJ75PaKg@mail.gmail.com>
Date:	Wed, 8 Oct 2014 16:46:55 -0700
From:	RR <rajaram.officemails@...il.com>
To:	Alexandre Courbot <gnurou@...il.com>
Cc:	Muthu Mani <muth@...ress.com>,
	Samuel Ortiz <sameo@...ux.intel.com>,
	Lee Jones <lee.jones@...aro.org>,
	Wolfram Sang <wsa@...-dreams.de>,
	Linus Walleij <linus.walleij@...aro.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Rajaram Regupathy <rera@...ress.com>,
	Johan Hovold <johan@...nel.org>
Subject: Re: [PATCH v3 3/3] gpio: add support for Cypress CYUSBS234 USB-GPIO adapter

On Wed, Oct 8, 2014 at 12:18 AM, Alexandre Courbot <gnurou@...il.com> wrote:
> On Wed, Oct 8, 2014 at 4:09 PM, Muthu Mani <muth@...ress.com> wrote:
>>> -----Original Message-----
>>> From: Alexandre Courbot [mailto:gnurou@...il.com]
>>> Sent: Tuesday, October 07, 2014 3:34 PM
>>> To: Muthu Mani
>>> Cc: Samuel Ortiz; Lee Jones; Wolfram Sang; Linus Walleij; Greg Kroah-
>>> Hartman; linux-i2c@...r.kernel.org; linux-gpio@...r.kernel.org; linux-
>>> usb@...r.kernel.org; Linux Kernel Mailing List; Rajaram Regupathy; Johan
>>> Hovold
>>> Subject: Re: [PATCH v3 3/3] gpio: add support for Cypress CYUSBS234 USB-
>>> GPIO adapter
>>>
>>> On Mon, Oct 6, 2014 at 11:47 PM, Muthu Mani <muth@...ress.com> wrote:
>>> > +
>>> > +static int cy_gpio_direction_input(struct gpio_chip *chip,
>>> > +                                       unsigned offset) {
>>> > +       return 0;
>>> > +}
>>> > +
>>> > +static int cy_gpio_direction_output(struct gpio_chip *chip,
>>> > +                                       unsigned offset, int value) {
>>> > +       return 0;
>>> > +}
>>>
>>> If that chip is capable of both output and input, shouldn't these functions be
>>> implemented? I think this has already been pointed out in a previous version
>>> but you did not reply.
>>
>> Thanks for your inputs.
>>
>> Only the GPIOs which are configured to be output GPIO can be set.
>
> In that case cy_gpio_set() should return an error for GPIOs which are
> not configured as outputs. Is that guaranteed by the current
> implementation?
>
>> The set operation would fail trying to set the input or unconfigured GPIOs.
>> In this version of driver, this support is not added, it can be introduced in future versions.
>> I will add a TODO note in the code.
>
> Argh, no TODO please. Actual code that will turn this code into a
> solid driver that can be merged.

Does a driver targeted for a custom device has to implement every
functionality in the 1st version ? My understanding is that Linux
follows incremental model and allows incremental merge.

(On a side note the driver is functionally verified with the necessary hardware)

Please correct me if I am missing something

>
> Can all GPIOs be set as input or output? If so, please implement
> cy_gpio_direction_*() and make sure that cy_gpio_set() behaves
> properly if a GPIO is not an output. If the input/output GPIOs are
> fixed, please make cy_gpio_direction_*() return an error if the GPIO
> capabilities does not correspond to what is asked, and again ensure
> that cy_gpio_set() works as expected.
> --
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