On 10/21/2015 06:12 AM, Oliver Neukum wrote:
> On Tue, 2015-10-20 at 14:16 -0400, Peter Hurley wrote:
>> ECHO is on by default and the cdc-acm driver does not implement the
>> put_char() and flush_chars() tty driver methods, which made the
>> problem
>> _way worse_, since every echoed char is sent as it's own URB.
>
> That can be fixed. How can I test this?
I'm working on getting my tty tests organized for upstreaming, but it's
not there yet. Let me see if I can get you a standalone test for
accuracy, at least.
> Will the tty layer use write() and put_char()?
Echoing uses put_char() + flush_chars() for echoing, if the driver
supports it; otherwise, it uses write().
Be aware that while the N_TTY line discipline ensures that put_char()
and write() usage will not be interleaved without flush_chars(), other
line disciplines might not, so at least be sure that driver won't
crash if that happens.
Regards,
Peter Hurley
> From ac75a2c9ea67ec22c704a6bcaa30e6fc415d64d3 Mon Sep 17 00:00:00 2001
> From: Oliver Neukum <oneukum@xxxxxxxx>
> Date: Wed, 21 Oct 2015 12:10:07 +0200
> Subject: [PATCH] cdc-acm: implement put_char() and flush_chars()
>
> This should cut down latencies and waste if the tty layer writes single bytes.
>
> Signed-off-by: Oliver Neukum >oneukum@xxxxxxxx>
> ---
> drivers/usb/class/cdc-acm.c | 58 +++++++++++++++++++++++++++++++++++++++++++++
> drivers/usb/class/cdc-acm.h | 1 +
> 2 files changed, 59 insertions(+)
>
> diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c
> index b30e742..262f179 100644
> --- a/drivers/usb/class/cdc-acm.c
> +++ b/drivers/usb/class/cdc-acm.c
> @@ -725,6 +725,62 @@ static int acm_tty_write(struct tty_struct *tty,
> return count;
> }
>
> +static void acm_tty_flush_chars(struct tty_struct *tty)
> +{
> + struct acm *acm = tty->driver_data;
> + struct acm_wb *cur = acm->putbuffer;
> + int err;
> + unsigned long flags;
> +
> + acm->putbuffer = NULL;
> + err = usb_autopm_get_interface_async(acm->control);
> + spin_lock_irqsave(&acm->write_lock, flags);
> + if (err < 0) {
> + cur->use = 0;
> + goto out;
> + }
> +
> + if (acm->susp_count) {
> + usb_anchor_urb(cur->urb, &acm->delayed);
> + goto out;
> + }
> +
> + acm_start_wb(acm, cur);
> +out:
> + spin_unlock_irqrestore(&acm->write_lock, flags);
> + return;
> +}
> +
> +static int acm_tty_put_char(struct tty_struct *tty, unsigned char ch)
> +{
> + struct acm *acm = tty->driver_data;
> + struct acm_wb *cur;
> + int wbn;
> + unsigned long flags;
> +
> +overflow:
> + cur = acm->putbuffer;
> + if (!cur) {
> + spin_lock_irqsave(&acm->write_lock, flags);
> + wbn = acm_wb_alloc(acm);
> + if (wbn >= 0) {
> + cur = &acm->wb[wbn];
> + acm->putbuffer = cur;
> + }
> + spin_unlock_irqrestore(&acm->write_lock, flags);
> + if (!cur)
> + return 0;
> + }
> +
> + if (cur->len == acm->writesize) {
> + acm_tty_flush_chars(tty);
> + goto overflow;
> + }
> +
> + cur->buf[cur->len++] = ch;
> + return 1;
> +}
> +
> static int acm_tty_write_room(struct tty_struct *tty)
> {
> struct acm *acm = tty->driver_data;
> @@ -1888,6 +1944,8 @@ static const struct tty_operations acm_ops = {
> .cleanup = acm_tty_cleanup,
> .hangup = acm_tty_hangup,
> .write = acm_tty_write,
> + .put_char = acm_tty_put_char,
> + .flush_chars = acm_tty_flush_chars,
> .write_room = acm_tty_write_room,
> .ioctl = acm_tty_ioctl,
> .throttle = acm_tty_throttle,
> diff --git a/drivers/usb/class/cdc-acm.h b/drivers/usb/class/cdc-acm.h
> index dd9af38..648a6f7 100644
> --- a/drivers/usb/class/cdc-acm.h
> +++ b/drivers/usb/class/cdc-acm.h
> @@ -94,6 +94,7 @@ struct acm {
> unsigned long read_urbs_free;
> struct urb *read_urbs[ACM_NR];
> struct acm_rb read_buffers[ACM_NR];
> + struct acm_wb *putbuffer; /* for acm_tty_put_char() */
> int rx_buflimit;
> int rx_endpoint;
> spinlock_t read_lock;
>
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