Hi.
I am currently trying to talk to my monitor using the hiddev USB interface.
Reading from the device works just fine, I can issue HIDIOCGDEVINFO, enumerate
the reports, fields and usages with HIDIOCGREPORTINFO, HIDIOCGFIELDINFO and
HIDIOCGUCODE/HIDIOCGUSAGE, and events from using the monitor OSD are delivered
to read(). So far, so good.
What I am failing at is writing a value to the device. The only documentation
I have found is usb/hiddev.txt in the linux kernel documentation tree.
According to this text, I have to prepare a struct hiddev_usage_ref with
the usage code and value I want to issue to the device, call HIDIOCSUSAGE,
prepare a struct hiddev_report_info and call HIDIOCSREPORT to send the
report containing the new values to the device.
I am hanging at the HIDIOCSUSAGE stage. No matter what values I enter into
the structure before sending the ioctl, I always get -EINVAL as the return
code.
The code in question is below. fd is an open file descriptor to the device
file. _ERROR, _DEBUG, _ENTER and _LEAVE are just helper macros which are
not important here.
Any thoughts on what I am doing wrong?
Thanks.
----------------------
void set_brightness(int fd, int brightness) {
struct hiddev_report_info report;
struct hiddev_usage_ref usage;
_ENTER;
usage.report_type = HID_REPORT_TYPE_INPUT;
usage.report_id = HID_REPORT_ID_UNKNOWN;
usage.usage_code = 0x00820010;
if (0 != ioctl(fd, HIDIOCGUSAGE, &usage)) {
_ERROR("Error during ioctl HIDIOCGUSAGE!");
_LEAVE;
}
_DEBUG("Usage found: report %08X, field %08X, usage %08X",
usage.report_id, usage.field_index, usage.usage_index);
usage.report_type = HID_REPORT_TYPE_OUTPUT;
usage.value = brightness;
if (0 != ioctl(fd, HIDIOCSUSAGE, &usage)) {
_ERROR("Error during ioctl HIDIOCSUSAGE!");
_LEAVE;
}
report.report_type = HID_REPORT_TYPE_OUTPUT;
report.report_id = 0;
report.num_fields = 1;
if (0 != ioctl(fd, HIDIOCSREPORT, &report)) {
_ERROR("Error during ioctl HIDIOCSREPORT!");
_LEAVE;
}
_LEAVE;
}
--
My Uncle Larry has a saying, "Never play proctologist with an unwilling
goose." Okay, so Uncle Larry drinks a bit. -- Yobaval
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