linux-kernel - Re: [PATCH v2] gpiolib: cdev: document that line eflags are shared

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Date:   Sat, 17 Oct 2020 07:39:13 +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] gpiolib: cdev: document that line eflags are shared

On Fri, Oct 16, 2020 at 05:24:14PM +0300, Andy Shevchenko wrote:
> On Wed, Oct 14, 2020 at 12:21 PM Kent Gibson <warthog618@...il.com> wrote:
> >
> > The line.eflags field is shared so document this fact and highlight it
> > throughout using READ_ONCE() and WRITE_ONCE() accessors.
> >
> > Also use a local copy of the eflags in edge_irq_thread() to ensure
> > consistent control flow even if eflags changes.  This is only a defensive
> > measure as edge_irq_thread() is currently disabled when the eflags are
> > changed.
> 
> > -       if (line->eflags == (GPIO_V2_LINE_FLAG_EDGE_RISING |
> > -                            GPIO_V2_LINE_FLAG_EDGE_FALLING)) {
> > +       eflags = READ_ONCE(line->eflags);
> > +       if (eflags == (GPIO_V2_LINE_FLAG_EDGE_RISING |
> > +                      GPIO_V2_LINE_FLAG_EDGE_FALLING)) {
> 
> Hmm... side note: perhaps at some point
> 
> #define GPIO_V2_LINE_FLAG_EDGE_BOTH  \
>         (GPIO_V2_LINE_FLAG_EDGE_RISING | GPIO_V2_LINE_FLAG_EDGE_FALLING)
> 
>        if (eflags == GPIO_V2_LINE_FLAG_EDGE_BOTH) {
> 
> ?

Yeah, that would make sense.  I think I used GPIO_V2_LINE_EDGE_FLAGS,
which is defined the same as your GPIO_V2_LINE_FLAG_EDGE_BOTH, here at
some point, but that just looked wrong.

The GPIO_V2_LINE_FLAG_EDGE_BOTH does read better.  I'll add it to the
todo list.

Cheers,
Kent.