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

[RR]

On Wed, Oct 8, 2014 at 12:18 AM, Alexandre Courbot <gnurou@xxxxxxxxx> wrote:
> On Wed, Oct 8, 2014 at 4:09 PM, Muthu Mani <muth@xxxxxxxxxxx> wrote:
>>> -----Original Message-----
>>> From: Alexandre Courbot [mailto:gnurou@xxxxxxxxx]
>>> 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@xxxxxxxxxxxxxxx; linux-gpio@xxxxxxxxxxxxxxx; linux-
>>> usb@xxxxxxxxxxxxxxx; 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@xxxxxxxxxxx> 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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