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. > > ++++++++++++++++++++++++++++++++++++++++++++++++++++++ > > > > I have doubts about the last sentence. It seems to me that for > > devices which do not use numbered reports, the first byte will > > be 0 and the report data begins in the second byte. > > > > This is based on testing results using hidapi and hidapitester, which > > use the ioctl. > > int HID_API_EXPORT hid_get_feature_report(hid_device *dev, unsigned > > char *data, size_t length) > > { > > int res; > > > > register_device_error(dev, NULL); > > > > res = ioctl(dev->device_handle, HIDIOCGFEATURE(length), data); > > if (res < 0) > > register_device_error_format(dev, "ioctl (GFEATURE): %s", > > strerror(errno)); > > > > return res; > > } > > > > Reference discussion: > > https://github.com/libusb/hidapi/issues/589 > > > > Test device is Jan Axelson's generic HID example which I have tested using > > libusb and hidapi across platforms as well as using Windows HID API. > > So I believe the FW is good. > > http://janaxelson.com/hidpage.htm#MyExampleCode (USB PIC MCU) > > > > Modified testing code from the following Linux kernel > samples/hidraw/hid-example.c > https://github.com/libusb/hidapi/issues/589#issuecomment-1597356054 > > Results are shown here. We can clearly see that the "Fake Report ID" 0 is > in the first byte of the returned buffer, matching the output from > hidapi/hidapitester, > > mcuee@UbuntuSwift3:~/build/hid/hidraw$ gcc -o myhid-example myhid-example.c > > mcuee@UbuntuSwift3:~/build/hid/hidraw$ sudo ./myhid-example > Report Descriptor Size: 47 > Report Descriptor: > 6 a0 ff 9 1 a1 1 9 3 15 0 26 ff 0 75 8 95 3f 81 2 9 4 15 0 26 ff 0 75 > 8 95 3f 91 2 9 5 15 0 26 ff 0 75 8 95 3f b1 2 c0 > > Raw Name: Microchip Technology Inc. Generic HID > Raw Phys: usb-0000:00:14.0-1/input0 > Raw Info: > bustype: 3 (USB) > vendor: 0x0925 > product: 0x7001 > ioctl HIDIOCSFEATURE returned: 64 > ioctl HIDIOCGFEATURE returned: 64 > Report data: > 0 41 42 43 44 45 46 47 48 14 4 18 4 4d 72 31 50 51 52 53 54 55 56 57 > 58 59 5a 5b 5c 5d 5e 5f 60 61 62 63 64 65 66 67 68 69 6a 6b 6c 6d 6e > 6f 70 71 72 73 74 75 76 77 78 79 7a 7b 7c 7d 7e 7f > > write() wrote 64 bytes > read() read 63 bytes: > 21 22 23 24 25 26 27 28 29 2a 2b 2c 2d 2e 2f 30 31 32 33 34 35 36 37 > 38 39 3a 3b 3c 3d 3e 3f 40 41 42 43 44 45 46 47 48 49 4a 4b 4c 4d 4e > 4f 50 51 52 53 54 55 56 57 58 59 5a 5b 5c 5d 5e 5f > Moreover the kernel codes here seem to prove that the documentation is wrong for both HIDIOCGFEATURE and HIDIOCGINPUT. https://github.com/torvalds/linux/blob/master/include/uapi/linux/hidraw.h /* The first byte of SFEATURE and GFEATURE is the report number */ #define HIDIOCSFEATURE(len) _IOC(_IOC_WRITE|_IOC_READ, 'H', 0x06, len) #define HIDIOCGFEATURE(len) _IOC(_IOC_WRITE|_IOC_READ, 'H', 0x07, len) #define HIDIOCGRAWUNIQ(len) _IOC(_IOC_READ, 'H', 0x08, len) /* The first byte of SINPUT and GINPUT is the report number */ #define HIDIOCSINPUT(len) _IOC(_IOC_WRITE|_IOC_READ, 'H', 0x09, len) #define HIDIOCGINPUT(len) _IOC(_IOC_WRITE|_IOC_READ, 'H', 0x0A, len) /* The first byte of SOUTPUT and GOUTPUT is the report number */ #define HIDIOCSOUTPUT(len) _IOC(_IOC_WRITE|_IOC_READ, 'H', 0x0B, len) #define HIDIOCGOUTPUT(len) _IOC(_IOC_WRITE|_IOC_READ, 'H', 0x0C, len) -- Xiaofan
