linux-kernel - Re: [PATCH v2 05/18] gpiolib: cdev: support GPIO_GET_LINE_IOCTL and GPIOLINE_GET_VALUES

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Date:   Sun, 26 Jul 2020 11:24:08 +0800
From:   Kent Gibson <warthog618@...il.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Linus Walleij <linus.walleij@...aro.org>
Subject: Re: [PATCH v2 05/18] gpiolib: cdev: support GPIO_GET_LINE_IOCTL and
 GPIOLINE_GET_VALUES_IOCTL

On Sun, Jul 26, 2020 at 09:12:44AM +0800, Kent Gibson wrote:
> On Sat, Jul 25, 2020 at 11:51:54PM +0300, Andy Shevchenko wrote:
> > On Sat, Jul 25, 2020 at 7:24 AM Kent Gibson <warthog618@...il.com> wrote:
> > >

[ snip ]
> > 
> > > +static bool padding_not_zeroed(__u32 *padding, int pad_size)
> > > +{
> > > +       int i, sum = 0;
> > > +
> > > +       for (i = 0; i < pad_size; i++)
> > > +               sum |= padding[i];
> > > +
> > > +       return sum;
> > > +}
> > 
> > Reimplementation of memchr_inv() ?
> > 
> 
> I was hoping to find an existing function, surely checking a region is
> zeroed is a common thing, right?, so this was a place holder as much
> as anything.  Not sure memchr_inv fits the bill, but I'll give it a
> try...
> 

I gave it a try.  It is a good fit functionally, but in my build it
results in a larger object by ~104 bytes.  I assume that is because 
padding_not_zeroed is being inlined, and otherwise optimized, while
memchr_inv calls aren't.

As such I'm inclined to leave it as is - unless there are other
objections.

Cheers,
Kent.