Hello,
We need to add comments about the synchronization, added inline:
Okash Khawaja, on lun. 03 avril 2017 21:21:29 +0100, wrote:
> +static int spk_ttyio_receive_buf2(struct tty_struct *tty,
> + const unsigned char *cp, char *fp, int count)
> +{
> + struct spk_ldisc_data *ldisc_data = (struct spk_ldisc_data *)tty->disc_data;
> +
> + if (spk_ttyio_synth->read_buff_add) {
> + int i;
> + for (i = 0; i < count; i++)
> + spk_ttyio_synth->read_buff_add(cp[i]);
> +
> + return count;
> + }
> +
> + if (ldisc_data->buf_free == 0)
/* ttyio_in will tty_schedule_flip */
> + return 0;
> +
/* Make sure the consumer has read buf before we have seen
* buf_free == 1 and overwrite buf */
> + mb();
> +
> + ldisc_data->buf = cp[0];
> + ldisc_data->buf_free--;
Don't decrement, set to 0. Decrementing would make the reader think
that there is potential for multi-character support, but with such a
lightweight synchronization there can't be. The fact that buf_free is 1
allows the tty part to set it to 0, but not more.
> +static unsigned char ttyio_in(int timeout)
> +{
> + struct spk_ldisc_data *ldisc_data =
> + (struct spk_ldisc_data *)speakup_tty->disc_data;
> + char rv;
> +
> + if (!down_timeout(&ldisc_data->sem, usecs_to_jiffies(timeout))) {
> + pr_warn("spk_ttyio: timeout (%d) while waiting for input\n",
> + timeout);
> + return 0xff;
> + }
> +
> + rv = ldisc_data->buf;
/* Make sure we have read buf before we set buf_free to let
* the producer overwrite it */
> + mb();
> + ldisc_data->buf_free = 1;
> + tty_schedule_flip(speakup_tty->port);
> + up(&ldisc_data->sem);
> Index: linux-staging/drivers/staging/speakup/spk_priv.h
> ===================================================================
> --- linux-staging.orig/drivers/staging/speakup/spk_priv.h
> +++ linux-staging/drivers/staging/speakup/spk_priv.h
> @@ -39,6 +39,7 @@
> #endif
>
> #define KT_SPKUP 15
> +#define SPK_SYNTH_TIMEOUT 100000
Please document the unit.
Samuel
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