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

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