On Fri, 12 Aug 2016 13:10:37 +0200,
Andrej Kruták wrote:
> > > +static void line6_hwdep_push_message(struct usb_line6 *line6)
> > > +{
> > > + unsigned long head = line6->buffer_circular.head;
> > > + /* The spin_unlock() and next spin_lock() provide needed ordering. */
> > > + unsigned long tail = ACCESS_ONCE(line6->buffer_circular.tail);
> > > +
> > > + if (!line6->buffer_circular.active)
> > > + return;
> > > +
> > > + if (CIRC_SPACE(head, tail, LINE6_MESSAGE_MAXCOUNT) >= 1) {
> > > + unsigned char *item = &line6->buffer_circular.data[
> > > + head * LINE6_MESSAGE_MAXLEN];
> > > + memcpy(item, line6->buffer_message, line6->message_length);
> > > + line6->buffer_circular.data_len[head] = line6->message_length;
> > > +
> > > + smp_store_release(&line6->buffer_circular.head,
> > > + (head + 1) & (LINE6_MESSAGE_MAXCOUNT - 1));
> > > + up(&line6->buffer_circular.sem);
> > > + }
> >
> > Hmm... this kind of a simple FIFO can be seen in anywhere in the
> > kernel code, and I'm sure that you can find an easier way to implement
> > it. The whole code looks a bit scary as it being home-brewed.
> >
>
> This code is based on Documentation/circular-buffers.txt, except for
> the semaphore magic.
The example there is basically a semi lock-free implementation. For
your purpose it's an overkill. This is no severely hot path, thus a
simpler version would make life easier.
> > Also, the blocking read/write control isn't usually done by a
> > semaphore. Then you can handle the interrupt there.
> >
> >
>
> I actually wonder why, semaphores seemed perfect for this... Do you
> have some hints?
Assume you want to interrupt the user-space app while it's being
blocked by the semaphore. With your code, you can't.
Takashi
_______________________________________________
Alsa-devel mailing list
Alsa-devel@xxxxxxxxxxxxxxxx
http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
