linux-kernel - Re: [PATCH 2/2] gpio: gpio-ftdi-cbus: add driver for FTDI CBUS GPIOs

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Date:	Wed, 15 Jul 2015 09:42:02 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Stefan Agner <stefan@...er.ch>
Cc:	Johan Hovold <johan@...nel.org>,
	Alexandre Courbot <gnurou@...il.com>,
	Grant Likely <grant.likely@...retlab.ca>,
	Greg KH <gregkh@...uxfoundation.org>,
	Sascha Silbe <x-linux@...ra-silbe.de>,
	Philipp Hachtmann <hachti@...hti.de>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] gpio: gpio-ftdi-cbus: add driver for FTDI CBUS GPIOs

On Sun, Jun 21, 2015 at 12:12 AM, Stefan Agner <stefan@...er.ch> wrote:

> This driver allows to use the CBUS pins, e.g. CBUS 0-3 on FT232R
> type of devices. Note that the pins need to be configured first
> by using I/O mode signal option in the EEPROM. This is _not_ the
> factory default configuration of any of the four pins.
>
> See also FTDI's Application Note AN_232R-01.
>
> Signed-off-by: Stefan Agner <stefan@...er.ch>

I see no big problems with this driver but I guess the serial portions
are the controversial parts.

> +++ b/drivers/gpio/gpio-ftdi-cbus.c
> @@ -0,0 +1,167 @@
> +/*
> + * gpiolib support for FTDI SIO chips supporting CBUS GPIO's (FT232R class)
> + *
> + * Copyright 2015 Stefan Agner
> + *
> + * Author: Stefan Agner <stefan@...er.ch>
> + *
> + *  This program is free software; you can redistribute  it and/or modify it
> + *  under  the terms of  the GNU General  Public License as published by the
> + *  Free Software Foundation;  either version 2 of the  License, or (at your
> + *  option) any later version.
> + *
> + * Note: To use the GPIOs on CBUS the signal option need to be set to
> + * I/O mode in EEPROM!
> + */
> +
> +#include <linux/kernel.h>
> +#include <linux/slab.h>
> +#include <linux/module.h>
> +#include <linux/gpio.h>

#include <linux/gpio/driver.h>

should be enough.

> +static int ftdi_cbus_gpio_direction_input(struct gpio_chip *chip,
> +                                         unsigned offset)
> +{
> +       struct ftdi_cbus_gpio *fcg = to_ftdi_cbus_gpio(chip);
> +
> +       fcg->cbus_mask &= ~((1 << offset) << 4);

I usually replace:

(1 << offset)

with

#include <linux/bitops.h>

BIT(offset)

so it's clear what is happening.

Yours,
Linus Walleij
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