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

From: Adam Kropelin
Date: Mon Aug 22 2005 - 16:56:47 EST


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

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