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

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Date:   Fri, 31 Jul 2020 18:05:10 +0200
From:   Bartosz Golaszewski <bgolaszewski@...libre.com>
To:     Kent Gibson <warthog618@...il.com>
Cc:     Andy Shevchenko <andy.shevchenko@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        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 3:12 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...
>

If you don't find an appropriate function: please put your new
implementation in lib/ so that others may reuse it.

> > ...
> >
> > > +static u64 gpioline_config_flags(struct gpioline_config *lc, int line_idx)
> > > +{
> > > +       int i;
> > > +
> > > +       for (i = lc->num_attrs - 1; i >= 0; i--) {
> >
> > Much better to read is
> >
> > unsigned int i = lc->num_attrs;
> >
> > while (i--) {
> >  ...
> > }
> >
>
> Really? I find that the post-decrement in the while makes determining the
> bounds of the loop more confusing.
>

Agreed, Andy: this is too much nit-picking. :)

[snip]

> > ...
> >
> > > +               struct gpio_desc *desc = gpiochip_get_desc(gdev->chip, offset);
> >
> > I prefer to see this split, but it's minor.
> >
> > > +               if (IS_ERR(desc)) {
> > > +                       ret = PTR_ERR(desc);
> > > +                       goto out_free_line;
> > > +               }
> >
> > ...
> >
> > > +               dev_dbg(&gdev->dev, "registered chardev handle for line %d\n",
> > > +                       offset);
> >
> > Perhaps tracepoint / event?
> >
>
> Again, a cut-and-paste from V1, and I have no experience with
> tracepoints or events, so I have no opinion on that.
>
> So, yeah - perhaps?
>

I think it's a good idea to add some proper instrumentation this time
other than much less reliable logs. Can you take a look at
include/trace/events/gpio.h? Adding new GPIO trace events should be
pretty straightforward by copy-pasti... drawing inspiration from
existing ones.

Bart