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

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Message-ID: <CAAVeFu+X0Lk=5sNm9kOwGX=2-DYN_-5v-7M9bAWXraffKsTkMg@mail.gmail.com>
Date:	Wed, 8 Oct 2014 16:18:36 +0900
From:	Alexandre Courbot <gnurou@...il.com>
To:	Muthu Mani <muth@...ress.com>
Cc:	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 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.

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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