linux-kernel - Re: [PATCH v2 07/18] gpiolib: cdev: support edge detection for uAPI v2

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Message-ID: <CAMpxmJW+RqW5=ugXru3ggRnLsPvtGEJ64_sBaY2GAXjeWT50qA@mail.gmail.com>
Date:   Tue, 4 Aug 2020 21:28:04 +0200
From:   Bartosz Golaszewski <bgolaszewski@...libre.com>
To:     Kent Gibson <warthog618@...il.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        linux-gpio <linux-gpio@...r.kernel.org>,
        Linus Walleij <linus.walleij@...aro.org>
Subject: Re: [PATCH v2 07/18] gpiolib: cdev: support edge detection for uAPI v2

On Sat, Jul 25, 2020 at 6:21 AM Kent Gibson <warthog618@...il.com> wrote:
>
> Add support for edge detection to lines requested using
> GPIO_GET_LINE_IOCTL.
>
> Signed-off-by: Kent Gibson <warthog618@...il.com>
> ---

[snip!]

> +
> +static irqreturn_t edge_irq_thread(int irq, void *p)
> +{
> +       struct edge_detector *edet = p;
> +       struct line *line = edet->line;
> +       struct gpio_desc *desc = edge_detector_desc(edet);
> +       struct gpioline_event le;
> +       int ret;
> +
> +       /* Do not leak kernel stack to userspace */
> +       memset(&le, 0, sizeof(le));
> +
> +       /*
> +        * We may be running from a nested threaded interrupt in which case
> +        * we didn't get the timestamp from edge_irq_handler().
> +        */
> +       if (!edet->timestamp) {
> +               le.timestamp = ktime_get_ns();

IIRC Marc suggested using smp_rmw() here before reading the timestamp.
Do we still need it or something changed?

Bartosz