Hi,
the theory that the lack of support for put_char() is a
major contributor to character loss in cdc-acm can be tested.
Sven, could you test the attached patch? It implements
the support.
Regards
Oliver
From f3871a76d7e2876b0e6ad66aee91085ecf9b2785 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 | 67 +++++++++++++++++++++++++++++++++++++++++++++
drivers/usb/class/cdc-acm.h | 1 +
2 files changed, 68 insertions(+)
diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c
index b30e742..1cb3124 100644
--- a/drivers/usb/class/cdc-acm.c
+++ b/drivers/usb/class/cdc-acm.c
@@ -712,9 +712,20 @@ static int acm_tty_write(struct tty_struct *tty,
}
if (acm->susp_count) {
+ if (acm->putbuffer) {
+ /* now to preserve order */
+ usb_anchor_urb(acm->putbuffer->urb, &acm->delayed);
+ acm->putbuffer = NULL;
+ }
usb_anchor_urb(wb->urb, &acm->delayed);
spin_unlock_irqrestore(&acm->write_lock, flags);
return count;
+ } else {
+ if (acm->putbuffer) {
+ /* at this point there is no good way to handle errors */
+ acm_start_wb(acm, acm->putbuffer);
+ acm->putbuffer = NULL;
+ }
}
stat = acm_start_wb(acm, wb);
@@ -725,6 +736,60 @@ 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);
+ else
+ 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 +1953,8 @@ 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;
--
2.1.4
