This reverts commit a81cf9799ad7299b03a4dff020d9685f9ac5f3e0.
The patch causes a regression, which I cannot find the reason for.
So let's revert for now, as a revert hurts only performance.
I was trying to resolve the problem with Oliver but we don't get any
conclusion
for 5 months, so I am now sending this to mail list and cdc_acm authors.
I am using simple request-response protocol to obtain the boiller
parameters
in constant intervals.
A simple one transaction is:
1. opening the /dev/ttyACM0
2. sending the following 10-bytes request to the device:
unsigned char req[] = {0x02, 0xfe, 0x01, 0x05, 0x08, 0x02, 0x01,
0x69, 0xab, 0x03};
3. reading response (frame of 74 bytes length).
4. closing the descriptor
I am doing this transaction with 5 seconds intervals.
Before the bad commit everything was working correctly: I've got a
requests and
a responses in a timely manner.
After the bad commit more time I am using the kernel module, more
problems I have.
The graph [2] is showing the problem.
As you can see after module load all seems fine but after about 30
minutes I've got
a plenty of EAGAINs when doing read()'s and trying to read back the
data.
When I rmmod and insmod the cdc_acm module again, then the situation is
starting
over again: running ok shortly after load, and more time it is running,
more EAGAINs
I have when calling read().
As a bonus I can see the problem on the device itself:
The device is configured as you can see here on this screen [3].
It has two transmision LEDs: TX and RX. Blink duration is set for 100ms.
This is a recording before the bad commit when all is working fine: [4]
And this is with the bad commit: [5]
As you can see the TX led is blinking wrongly long (indicating
transmission?)
and I have problems doing read() calls (EAGAIN).
Reported-by: manio <manio@xxxxxxxxxx>
Signed-off-by: Oliver Neukum <oneukum@xxxxxxxx>
Fixes: a81cf9799ad7299b03a4dff020d9685f9ac5f3e0
---
drivers/usb/class/cdc-acm.c | 92 ---------------------------------------------
drivers/usb/class/cdc-acm.h | 1 -
2 files changed, 93 deletions(-)
diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c
index f95bbdc86578..f9b40a9dc4d3 100644
--- a/drivers/usb/class/cdc-acm.c
+++ b/drivers/usb/class/cdc-acm.c
@@ -780,20 +780,9 @@ 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);
@@ -804,85 +793,6 @@ 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;
- int err;
- unsigned long flags;
-
- spin_lock_irqsave(&acm->write_lock, flags);
-
- cur = acm->putbuffer;
- if (!cur) /* nothing to do */
- goto out;
-
- acm->putbuffer = NULL;
- err = usb_autopm_get_interface_async(acm->control);
- if (err < 0) {
- cur->use = 0;
- acm->putbuffer = cur;
- dev_dbg(&acm->control->dev, "Resumption failure\n");
- goto out;
- }
-
- if (acm->susp_count) {
- dev_dbg(&acm->control->dev, "Anchored buffer of %u at %p \n", cur->len, cur);
- usb_anchor_urb(cur->urb, &acm->delayed);
- } else {
- dev_dbg(&acm->control->dev, "Writing out buffer of %u at %p \n", cur->len, cur);
- 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) {
- dev_dbg(&acm->control->dev, "Allocation failed\n");
- return 0;
- } else {
- dev_dbg(&acm->control->dev, "Allocated new buffer %d at %p \n",
- wbn, cur);
- }
- }
-
- dev_dbg(&acm->control->dev, "Writing character %u at position %d in buffer %p\n",
- ch, cur->len, cur);
-
- if (cur->len == acm->writesize) {
- dev_dbg(&acm->control->dev, "Flush overdue\n");
- /* this is now the error case */
- acm_tty_flush_chars(tty);
- goto overflow;
- }
-
- cur->buf[cur->len++] = ch;
- if (cur->len == acm->writesize) {
- dev_dbg(&acm->control->dev, "Triggering a flush\n");
- acm_tty_flush_chars(tty);
- }
-
- return 1;
-}
-
static int acm_tty_write_room(struct tty_struct *tty)
{
struct acm *acm = tty->driver_data;
@@ -2006,8 +1916,6 @@ 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 eacc116e83da..ca06b20d7af9 100644
--- a/drivers/usb/class/cdc-acm.h
+++ b/drivers/usb/class/cdc-acm.h
@@ -96,7 +96,6 @@ 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;
spinlock_t read_lock;
u8 *notification_buffer; /* to reassemble fragmented notifications */
--
2.16.4
