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SubjectRe: [PATCH v8 09/20] gpiolib: cdev: support edge detection for uAPI v2
On Tue, Sep 15, 2020 at 01:39:41PM +0300, Andy Shevchenko wrote:
> On Wed, Sep 9, 2020 at 1:33 PM Kent Gibson <warthog618@gmail.com> wrote:
> >
> > Add support for edge detection to lines requested using
> > GPIO_V2_GET_LINE_IOCTL.
> >
> > The edge_detector implementation is based on the v1 lineevent
> > implementation.
>
> ...
>
[snip]
> > +
> > + /*
> > + * We may be running from a nested threaded interrupt in which case
> > + * we didn't get the timestamp from edge_irq_handler().
> > + */
>
> > + if (!line->timestamp) {
>
> Can it be positive conditional?
>

Not sure what you mean - switch the order of the if/else?

> > + le.timestamp = ktime_get_ns();
> > + if (lr->num_lines != 1)
> > + line->req_seqno = atomic_inc_return(&lr->seqno);
> > + } else {
> > + le.timestamp = line->timestamp;
> > + }
> > + line->timestamp = 0;
> > +
> > + if (line->eflags == (GPIO_V2_LINE_FLAG_EDGE_RISING |
> > + GPIO_V2_LINE_FLAG_EDGE_FALLING)) {
> > + int level = gpiod_get_value_cansleep(line->desc);
> > +
> > + if (level)
> > + /* Emit low-to-high event */
> > + le.id = GPIO_V2_LINE_EVENT_RISING_EDGE;
> > + else
> > + /* Emit high-to-low event */
> > + le.id = GPIO_V2_LINE_EVENT_FALLING_EDGE;
> > + } else if (line->eflags == GPIO_V2_LINE_FLAG_EDGE_RISING) {
> > + /* Emit low-to-high event */
> > + le.id = GPIO_V2_LINE_EVENT_RISING_EDGE;
> > + } else if (line->eflags == GPIO_V2_LINE_FLAG_EDGE_FALLING) {
> > + /* Emit high-to-low event */
> > + le.id = GPIO_V2_LINE_EVENT_FALLING_EDGE;
> > + } else {
> > + return IRQ_NONE;
> > + }
> > + line->line_seqno++;
> > + le.line_seqno = line->line_seqno;
> > + le.seqno = (lr->num_lines == 1) ? le.line_seqno : line->req_seqno;
> > + le.offset = gpio_chip_hwgpio(line->desc);
> > +
> > + ret = kfifo_in_spinlocked_noirqsave(&lr->events, &le,
> > + 1, &lr->wait.lock);
> > + if (ret)
> > + wake_up_poll(&lr->wait, EPOLLIN);
> > + else
>
> > + pr_debug_ratelimited("event FIFO is full - event dropped\n");
>
> Oh, can we really avoid printf() in IRQ context?
>

Even in the IRQ thread? Would a tracepoint be preferable?

Btw, this is drawn from the v1 implmentation.

> > +
> > +static void edge_detector_stop(struct line *line)
> > +{
>
> > + if (line->irq) {
> > + free_irq(line->irq, line);
> > + line->irq = 0;
> > + }
>
> Perhaps
>
> if (!line->irq)
> return;
>
> ?
>

No - the function is extended in subsequent patches. I usually make a
note of cases like this in the commentary, but missed this one.

> > + if (!eflags)
> > + return 0;
> > +
> > + irq = gpiod_to_irq(line->desc);
> > + if (irq <= 0)
>
> > + return -ENODEV;
>
> Why shadowing actual error code?
>

Another one drawn from the v1 implementation, so not sure.
gpiod_to_irq() can potentially return EINVAL, which is definitely not
appropriate to return, or ENXIO, which is actually more appropriate??

Cheers,
Kent.

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