[PATCH] hiddev: output reports are dropped when HIDIOCSREPORT is called in short succession

[PATCH] hiddev: output reports are dropped when HIDIOCSREPORT is called in short succession

[Stefan Nickl]

[-- Attachment #1: Type: text/plain, Size: 881 bytes --]

Hi,

when trying to make the hiddev driver issue several Set_Report control
transfers to a custom device with 2.6.13-rc6, only the first transfer in
a row is carried out, while others immediately following it are silently
dropped.

This happens where hid_submit_report() (in hid-core.c) tests for
HID_CTRL_RUNNING, which seems to be still set because the first transfer
is not finished yet.

As a workaround, inserting a delay between the two calls to
ioctl(HIDIOCSREPORT) in userspace "solves" the problem.
The straightforward fix is to add a call to hid_wait_io() to the
implementation of HIDIOCSREPORT (in hiddev.c), just like for
HIDIOCGREPORT. Works fine for me.

Apparently, this issue has some history:
http://marc.theaimsgroup.com/?l=linux-usb-users&m=111100670105558&w=2

Signed-off-by: Stefan Nickl <Stefan.Nickl@kontron.com>

-- 
Stefan Nickl
Kontron Modular Computers


[-- Attachment #2: hiddev_HIDIOCSREPORT_wait_io.patch --]
[-- Type: text/x-patch, Size: 332 bytes --]

--- v2.6.13-rc6/drivers/usb/input/hiddev.c.orig	2005-08-22 10:56:55.000000000 +0200
+++ v2.6.13-rc6/drivers/usb/input/hiddev.c	2005-08-22 10:57:07.000000000 +0200
@@ -507,6 +507,7 @@ static int hiddev_ioctl(struct inode *in
 			return -EINVAL;
 
 		hid_submit_report(hid, report, USB_DIR_OUT);
+		hid_wait_io(hid);
 
 		return 0;
 

Re: [linux-usb-devel] [PATCH] hiddev: output reports are dropped when HIDIOCSREPORT is called in short succession

[Adam Kropelin]

Stefan Nickl wrote:
> Hi,
>
> when trying to make the hiddev driver issue several Set_Report control
> transfers to a custom device with 2.6.13-rc6, only the first transfer
> in a row is carried out, while others immediately following it are
> silently dropped.
>
> This happens where hid_submit_report() (in hid-core.c) tests for
> HID_CTRL_RUNNING, which seems to be still set because the first
> transfer is not finished yet.
>
> As a workaround, inserting a delay between the two calls to
> ioctl(HIDIOCSREPORT) in userspace "solves" the problem.
> The straightforward fix is to add a call to hid_wait_io() to the
> implementation of HIDIOCSREPORT (in hiddev.c), just like for
> HIDIOCGREPORT. Works fine for me.

Yup, I've seen the same issue on the apcupsd project. I added the 
hid_wait_io() call to HIDIOCGREPORT a while back since it used to suffer 
from the same problem. I'd have no objection to making HIDIOCSREPORT 
synchronous as well.

--Adam