linux-kernel - Re: [PATCH v3 2/8] gpio: 104-idio-16: Implement get

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Date:   Wed, 21 Mar 2018 12:04:50 -0400
From:   William Breathitt Gray <vilhelm.gray@...il.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-iio@...r.kernel.org
Subject: Re: [PATCH v3 2/8] gpio: 104-idio-16: Implement get_multiple callback

On Wed, Mar 21, 2018 at 05:32:03PM +0200, Andy Shevchenko wrote:
>On Sat, Mar 17, 2018 at 5:50 PM, William Breathitt Gray
><vilhelm.gray@...il.com> wrote:
>> The ACCES I/O 104-IDIO-16 series of devices provides 16
>> optically-isolated digital inputs accessed via two 8-bit ports. Since
>> eight input lines are acquired on a single port input read, the
>> 104-IDIO-16 GPIO driver may improve multiple input reads by utilizing a
>> get_multiple callback. This patch implements the
>> idio_16_gpio_get_multiple function which serves as the respective
>> get_multiple callback.
>
>> +static int idio_16_gpio_get_multiple(struct gpio_chip *chip,
>> +       unsigned long *mask, unsigned long *bits)
>> +{
>> +       struct idio_16_gpio *const idio16gpio = gpiochip_get_data(chip);
>> +
>> +       *bits = 0;
>
>> +       if (*mask & 0xFF0000)
>
>GENMASK(23, 16) ?
>
>> +               *bits |= (unsigned long)inb(idio16gpio->base + 1) << 16;
>
>Do you need casting?
>
>> +       if (*mask & 0xFF000000)
>
>GENMASK(31, 24) ?
>
>Alternative (and for above):
>
>(*mask >> 24) & 0xff
>
>(*mask >> 16) & 0xff

That's a good suggestion since GENMASK would be useful in making it
clear which bits we are actually checking; the literal bitmasks such as
0xFF000000 can be difficult to read at a glance. I'll incorporate
GENMASK into a version 4 release of this patch.

>
>
>> +               *bits |= (unsigned long)inb(idio16gpio->base + 5) << 24;
>
>Do you need casting?

The inb function returns a u8, which is typically a typedef of an
unsigned char. Since u8 only guaranteed a range of 8 bits, we require a
cast to unsigned long to guarantee that the left shifted value stays
intact as a 32-bit unsigned value rather than wrap around an 8-bit
unsigned range.

William Breathitt Gray

>
>> +
>> +       return 0;
>> +}
>> +
>>  static void idio_16_gpio_set(struct gpio_chip *chip, unsigned offset, int value)
>>  {
>>         struct idio_16_gpio *const idio16gpio = gpiochip_get_data(chip);
>> @@ -244,6 +258,7 @@ static int idio_16_probe(struct device *dev, unsigned int id)
>>         idio16gpio->chip.direction_input = idio_16_gpio_direction_input;
>>         idio16gpio->chip.direction_output = idio_16_gpio_direction_output;
>>         idio16gpio->chip.get = idio_16_gpio_get;
>> +       idio16gpio->chip.get_multiple = idio_16_gpio_get_multiple;
>>         idio16gpio->chip.set = idio_16_gpio_set;
>>         idio16gpio->chip.set_multiple = idio_16_gpio_set_multiple;
>>         idio16gpio->base = base[id];
>> --
>> 2.16.2
>>
>
>
>
>-- 
>With Best Regards,
>Andy Shevchenko