On Wed, Jun 21, 2023 at 11:05 PM Benjamin Tissoires <benjamin.tissoires@xxxxxxxxxx> wrote: > > On Wed, Jun 21, 2023 at 1:27 PM Xiaofan Chen <xiaofanc@xxxxxxxxx> wrote: > > > > On Tue, Jun 20, 2023 at 7:28 AM Xiaofan Chen <xiaofanc@xxxxxxxxx> wrote: > > > > > > On Mon, Jun 19, 2023 at 11:14 PM Xiaofan Chen <xiaofanc@xxxxxxxxx> wrote: > > > > > > > > On Mon, Jun 19, 2023 at 2:09 PM Xiaofan Chen <xiaofanc@xxxxxxxxx> wrote: > > > > > > > > > > I know that thurrent documentation has been there since it was created by > > > > > Alan Ott many years ago. And he started the HIDAPI project around that > > > > > time as well. However, I am starting to doubt whether it is correct or not > > > > > based on the testing using HIDAPI. > > > > > > > > > > Please help to clarify. Thanks. > > > > > > > > > > https://docs.kernel.org/hid/hidraw.html > > > > > +++++++++++++++++++++++++++++++++++++++++++++++++++++ > > > > > HIDIOCGFEATURE(len): > > > > > > > > > > Get a Feature Report > > > > > > > > > > This ioctl will request a feature report from the device using the > > > > > control endpoint. The first byte of the supplied buffer should be > > > > > set to the report number of the requested report. For devices > > > > > which do not use numbered reports, set the first byte to 0. The > > > > > returned report buffer will contain the report number in the first > > > > > byte, followed by the report data read from the device. For devices > > > > > which do not use numbered reports, the report data will begin at the > > > > > first byte of the returned buffer. > > > Yep, this is wrong. > > This should be read: > ``` > The returned report buffer will contain the report number in the first > byte or 0 when the device doesn't use numbered reports. The data read > from the device will be stored in the following bytes. > ``` > > FWIW, the difficulty to find out what the code does is because this part > is handled in each HID transport driver: USB, Bluetooth, I2C. > > Looking at drivers/hid/usbhid/hid-core.c, lines 869+, the function > usbhid_get_raw_report() is the one used by hidraw in the end and is > still the original code from Alan: > > ``` > /* Byte 0 is the report number. Report data starts at byte 1.*/ > buf[0] = report_number; > if (report_number == 0x0) { > /* Offset the return buffer by 1, so that the report ID > will remain in byte 0. */ > buf++; > count--; > skipped_report_id = 1; > } > ``` > > > Hi Jiri and Benjamin, > > > > Sorry to ping the two maintainers, hopefully you two can give the > > answer. Thanks. > > See above, I also think the documentation is wrong. > Thanks a lot for the confirmation. On the same note, I think it is the same for HIDIOCGINPUT as well, but there is no need to update the documentation once the documentation is fixed for HIDIOCGFEATURE. ++++++++++++++ HIDIOCGINPUT(len): Get an Input Report This ioctl will request an input report from the device using the control endpoint. This is slower on most devices where a dedicated In endpoint exists for regular input reports, but allows the host to request the value of a specific report number. Typically, this is used to request the initial states of an input report of a device, before an application listens for normal reports via the regular device read() interface. The format of the buffer issued with this report is identical to that of HIDIOCGFEATURE. ++++++++++++++ -- Xiaofan
