On Tue, 2014-04-08 at 09:33 +0200, Johan Hovold wrote:
> On Tue, Apr 08, 2014 at 11:05:20AM +0800, Xiao Jin wrote:
> > We find two problems on acm tty write delayed mechanism.
>
> Then you should split this into two patches.
>
> > (1) When acm resume, the delayed wb will be started. But now
> > only one write can be saved during acm suspend. More acm write
> > may be abandoned.
>
> Why not simply return 0 in write and use the tty buffering rather than
> implement another buffer in cdc_acm?
Yes. We need a single buffer because the tty layer is not happy
when you accept no data. But we should be able to refuse subsequent
writes. Could you test this patch?
Regards
Oliver
>From 1d44c1f2a10b5617824a37c8ec51f5547e482259 Mon Sep 17 00:00:00 2001
From: Oliver Neukum <oneukum@xxxxxxx>
Date: Tue, 8 Apr 2014 12:17:39 +0200
Subject: [PATCH] cdc-acm: fix consecutive writes while device is suspended
CDC-ACM needs to handle one attempt to write to a suspended
device because we told the tty layer that there is room.
A second attempt may and must fail or we drop data.
Signed-off-by: Oliver Neukum <oneukum@xxxxxxx>
CC: stable@xxxxxxxxxxxxxxx
---
drivers/usb/class/cdc-acm.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c
index 900f7ff..7ad3105 100644
--- a/drivers/usb/class/cdc-acm.c
+++ b/drivers/usb/class/cdc-acm.c
@@ -646,10 +646,12 @@ static int acm_tty_write(struct tty_struct *tty,
usb_autopm_get_interface_async(acm->control);
if (acm->susp_count) {
- if (!acm->delayed_wb)
+ if (!acm->delayed_wb) {
acm->delayed_wb = wb;
- else
+ } else {
usb_autopm_put_interface_async(acm->control);
+ count = 0;
+ }
spin_unlock_irqrestore(&acm->write_lock, flags);
return count; /* A white lie */
}
--
1.8.4.5
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