linux-kernel - Re: [PATCH 5/8] gpio: exar: Fix reading of directions and values

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Date:   Thu, 18 May 2017 12:16:15 +0200
From:   Jan Kiszka <jan.kiszka@...mens.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Alexandre Courbot <gnurou@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        Sudip Mukherjee <sudip.mukherjee@...ethink.co.uk>,
        Sascha Weisenberger <sascha.weisenberger@...mens.com>
Subject: Re: [PATCH 5/8] gpio: exar: Fix reading of directions and values

On 2017-05-18 12:11, Andy Shevchenko wrote:
> On Thu, May 18, 2017 at 8:20 AM, Jan Kiszka <jan.kiszka@...mens.com> wrote:
>> On 2017-05-13 15:36, Andy Shevchenko wrote:
>>> On Sat, May 13, 2017 at 10:29 AM, Jan Kiszka <jan.kiszka@...mens.com> wrote:
>>>> First, the logic for translating a register bit to the return code of
>>>> exar_get_direction and exar_get_value were wrong. And second, there was
>>>> a flip regarding the register bank in exar_get_direction.
>>>
>>> Again, I wish it was tested in the first place.
>>>
>>> After addressing below:
>>> FWIW:
>>> Reviewed-by: Andy Shevchenko <andy.shevchenko@...il.com>
>>>
>>>> @@ -68,7 +68,7 @@ static int exar_get(struct gpio_chip *chip, unsigned int reg)
>>>>         value = readb(exar_gpio->regs + reg);
>>>>         mutex_unlock(&exar_gpio->lock);
>>>>
>>>> -       return !!value;
>>>> +       return value;
>>>
>>> This one is correct.
> 
>>>
>>>> @@ -80,7 +80,7 @@ static int exar_get_direction(struct gpio_chip *chip, unsigned int offset)
>>>>         addr = bank ? EXAR_OFFSET_MPIOSEL_HI : EXAR_OFFSET_MPIOSEL_LO;
>>>>         val = exar_get(chip, addr) >> (offset % 8);
>>>>
>>>> -       return !!val;
>>>> +       return val & 1;
>>>
>>> It should be rather
>>>
>>>         val = exar_get(chip, addr) & BIT(offset % 8);
>>
>> That won't give us 0 or 1 as return value, thus would be incorrect.
> 
> Full picture:
> 
>  val = exar_get(chip, addr) & BIT(offset % 8);
> 
>  return !!val;
> 
> How it could be non-(1 or 0)?
> 

Right - but what is the point of that other style?

Jan

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