From: Alan Ott <alan@signal11.us>
Make hidraw not stick an extra byte on the beginning of an IN transfer
when a HID device contains multiple reports.
Signed-off-by: Alan Ott <alan@signal11.us>
---
In drivers/hid/hid-core.c, hid_report_raw_event() does the following to
pass the raw data to hidraw:
if (hid->claimed & HID_CLAIMED_HIDRAW) {
/* numbered reports need to be passed with the report num */
if (report_enum->numbered)
hidraw_report_event(hid, data - 1, size + 1);
else
hidraw_report_event(hid, data, size);
}
The data-1 and size+1 add an extra byte to he beginning of the data
which is _not_ the report number. The report number is located at
data[0], not data[-1].
I followed the data all the way from its source in the urb:
1. drivers/hid/usbhid/hid-core.c passes urb->transfer_buffer to
2. hid_input_report() (drivers/hid/hid-core.c) who passes it to
3. hid_report_raw_event() (drivers/hid/hid-core.c), who passes data-1 to
4. hidraw_report_event() (drivers/hid/hidraw.c), which puts the data in
a buffer for hidraw_read() to pick up.
Nothing in the chain indicates that the data pointer which arrives in
hid_report_raw_event() is offset by one.
From a multi-report HID device, I can send 4 bytes (report number + 3
data bytes) and see a return of 5 bytes from read() (hidraw_read())
which is the data I would expect with an extra byte (0x0) stuck to the
beginning of it.
I have attached a patch which seems to take care of this problem. Please
let me know if I have completely misjudged the situation.
Alan.
diff --git a/drivers/hid/hid-core.c b/drivers/hid/hid-core.c
index 2e2aa75..0e4a6fb 100644
--- a/drivers/hid/hid-core.c
+++ b/drivers/hid/hid-core.c
@@ -1043,13 +1043,8 @@ void hid_report_raw_event(struct hid_device *hid, int type, u8 *data, int size,
if ((hid->claimed & HID_CLAIMED_HIDDEV) && hid->hiddev_report_event)
hid->hiddev_report_event(hid, report);
- if (hid->claimed & HID_CLAIMED_HIDRAW) {
- /* numbered reports need to be passed with the report num */
- if (report_enum->numbered)
- hidraw_report_event(hid, data - 1, size + 1);
- else
- hidraw_report_event(hid, data, size);
- }
+ if (hid->claimed & HID_CLAIMED_HIDRAW)
+ hidraw_report_event(hid, data, size);
for (a = 0; a < report->maxfield; a++)
hid_input_field(hid, report->field[a], cdata, interrupt);
--
