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SubjectRe: [PATCH] cdc-acm: some enhancement on acm delayed write
From
Date
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@suse.de>
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@suse.de>
CC: stable@vger.kernel.org
---
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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