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    SubjectRe: [PATCH] drivers/isdn/gigaset: new M101 driver
    Thanks, Andrew, for your review. Some replies:

    Am 02.02.2007 02:13 schrieb Andrew Morton:
    > On Thu, 1 Feb 2007 22:12:24 +0100
    > Tilman Schmidt <tilman@imap.cc> wrote:
    >
    >> +/* Kbuild sometimes doesn't set this */
    >> +#ifndef KBUILD_MODNAME
    >> +#define KBUILD_MODNAME "asy_gigaset"
    >> +#endif
    >
    > That's a subtle way of reporting a kbuild bug ;)
    >
    > What's the story here?

    If an object file is linked into more than one module (like
    asyncdata.o which is linked into both ser_gigaset and usb_gigaset)
    then Kbuild compiles it only once but cannot decide which of the
    module names to put into KBUILD_MODNAME, so it takes the easy way
    out and doesn't define KBUILD_MODNAME at all. I'm not sure if
    that qualifies as a kbuild bug. I'd rather call it a limitation.

    >> +static int write_modem(struct cardstate *cs)
    >> +{
    >> + struct tty_struct *tty = cs->hw.ser->tty;
    >> + struct bc_state *bcs = &cs->bcs[0]; /* only one channel */
    >> + struct sk_buff *skb = bcs->tx_skb;
    >> + int sent;
    >> +
    >> + if (!tty || !tty->driver || !skb)
    >> + return -EFAULT;
    >
    > Is EFAULT appropriate?

    It hardly matters, as it isn't propagated anywhere. -1 would
    work just as well.

    > Can all these things happen?

    Theoretically no, but this is called from a tasklet and I have
    already traced a bug which made one of these disappear. Not
    having the kernel crash completely in such an event considerably
    helps debugging.

    >> + set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
    >
    > Is a client of the tty interface supposed to be diddling tty flags like this?

    Documentation/tty.txt says so. (Yes, I wrote that part myself,
    but nobody protested. ;-) Also, the PPP line discipline does
    the same.

    >> + spin_lock_irqsave(&cs->cmdlock, flags);
    >> + cb = cs->cmdbuf;
    >> + spin_unlock_irqrestore(&cs->cmdlock, flags);
    >
    > It is doubtful if the locking here does anything useful.

    It assures atomicity when reading the cs->cmdbuf pointer.

    >> + spin_lock_irqsave(&cs->cmdlock, flags);
    >> + cb->prev = cs->lastcmdbuf;
    >> + if (cs->lastcmdbuf)
    >> + cs->lastcmdbuf->next = cb;
    >> + else {
    >> + cs->cmdbuf = cb;
    >> + cs->curlen = len;
    >> + }
    >> + cs->cmdbytes += len;
    >> + cs->lastcmdbuf = cb;
    >> + spin_unlock_irqrestore(&cs->cmdlock, flags);
    >
    > Would the use of list_heads simplify things here?

    I don't think so. The operations in list.h do not keep track of
    the total byte count, and adding that in a race-free way appears
    non-trivial.

    >> +/*
    >> + * Free hardware specific device data
    >> + * This will be called by "gigaset_freecs" in common.c
    >> + */
    >> +static void gigaset_freecshw(struct cardstate *cs)
    >> +{
    >> + tasklet_kill(&cs->write_tasklet);
    >
    > Does tasklet kill() wait for the tasklet to stop running on a different
    > CPU? I thing so, but it was written in the days before we commented code.

    Its description in LDD3 ch. 7 seems to imply that it does.

    >> + down(&cs->hw.ser->dead_sem);
    >
    > Does this actually use the semaphore's counting feature? If not, can we
    > switch it to a mutex?

    I stole that code from the PPP line discipline. It is to assure all
    other ldisc methods have completed before the close method proceeds.
    This doesn't look like a case for a mutex to me, but I'm open to
    suggestions if it's important to avoid a semaphore here.

    >> + tail = atomic_read(&inbuf->tail);
    >> + head = atomic_read(&inbuf->head);
    >> + gig_dbg(DEBUG_INTR, "buffer state: %u -> %u, receive %u bytes",
    >> + head, tail, count);
    >> +
    >> + if (head <= tail) {
    >> + n = RBUFSIZE - tail;
    >> + if (count >= n) {
    >> + /* buffer wraparound */
    >> + memcpy(inbuf->data + tail, buf, n);
    >> + tail = 0;
    >> + buf += n;
    >> + count -= n;
    >> + } else {
    >> + memcpy(inbuf->data + tail, buf, count);
    >> + tail += count;
    >> + buf += count;
    >> + count = 0;
    >> + }
    >> + }
    >
    > Perhaps the (fairly revolting) circ_buf.h can be used for this stuff.

    It probably could, but IMHO readability would suffer rather than improve.

    Thanks,
    Tilman

    PS: My patch hasn't appeared on LKML so far. Any idea why?

    --
    Tilman Schmidt E-Mail: tilman@imap.cc
    Bonn, Germany
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