Hi ,
i am trying to send a vendor specific HID report from a userspace host
program to vendor usb hid device
using HIDRAW interface .
the vendor specific report consist of < "Report ID " (0th position ) >
followed by < "payload of data " > .
when i send report in this format , i am not getting report response
from the usb device .
but when i send report in the format < "Report ID "(0th byte ) >
<Report ID (1st byte )> < "data payload ">
i am getting perfect report response from usb device .
when i debugged kernel source code , i found the function
usbhid_output_raw_report function defined in
drivers/hid/usbhid/hid-core.c
responsible for report transfer , where we use usb_control_msg as :
ret = usb_control_msg(dev, usb_sndctrlpipe(dev, 0),
HID_REQ_SET_REPORT,
USB_DIR_OUT | USB_TYPE_CLASS | USB_RECIP_INTERFACE,
cpu_to_le16(((HID_OUTPUT_REPORT + 1) << 8) | *buf),
interface->desc.bInterfaceNumber, buf + 1, count - 1,
USB_CTRL_SET_TIMEOUT);
As we can see above we are passing " buf + 1 " , " count - 1 " to
data and size parameters of usb_control_msg() function ,
which effectively means that if i make my report format as <report id
> < payload >
then in the data parameter of usb_control_msg function , report id is
stripped off () .
and thats why i am not getting response with above report format .
report responses comes fine if i modify usb_control_msg usage as below :
ret = usb_control_msg(dev, usb_sndctrlpipe(dev, 0),
HID_REQ_SET_REPORT,
USB_DIR_OUT | USB_TYPE_CLASS | USB_RECIP_INTERFACE,
cpu_to_le16(((HID_OUTPUT_REPORT + 1) << 8) | *buf),
interface->desc.bInterfaceNumber, buf , count ,
USB_CTRL_SET_TIMEOUT);
here i passed complete buf and count thereby passing < report id >
also in data params of usb_control_msg .
kindly provide insight and clarity regarding the < report id > ambiguity .
the original usbhid_output_raw_report() function is copied below for
reference .
static int usbhid_output_raw_report(struct hid_device *hid, __u8 *buf,
size_t count)
{
struct usbhid_device *usbhid = hid->driver_data;
struct usb_device *dev = hid_to_usb_dev(hid);
struct usb_interface *intf = usbhid->intf;
struct usb_host_interface *interface = intf->cur_altsetting;
int ret;
printk("=====>[IPOD HID ][Hid-core.c]%s\n" , __FUNCTION__);
ret = usb_control_msg(dev, usb_sndctrlpipe(dev, 0),
HID_REQ_SET_REPORT,
USB_DIR_OUT | USB_TYPE_CLASS | USB_RECIP_INTERFACE,
cpu_to_le16(((HID_OUTPUT_REPORT + 1) << 8) | *buf),
interface->desc.bInterfaceNumber, buf + 1, count - 1,
USB_CTRL_SET_TIMEOUT);
/* count also the report id */
if (ret > 0)
ret++;
return ret;
}
Thanx & Regards
Amit Nagal
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