From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4F1A4EB64D9 for ; Mon, 19 Jun 2023 15:14:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229649AbjFSPOU (ORCPT ); Mon, 19 Jun 2023 11:14:20 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35170 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231151AbjFSPOT (ORCPT ); Mon, 19 Jun 2023 11:14:19 -0400 Received: from mail-yw1-x1132.google.com (mail-yw1-x1132.google.com [IPv6:2607:f8b0:4864:20::1132]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5BCCCBD for ; Mon, 19 Jun 2023 08:14:17 -0700 (PDT) Received: by mail-yw1-x1132.google.com with SMTP id 00721157ae682-570808d8ddeso34371427b3.0 for ; Mon, 19 Jun 2023 08:14:17 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20221208; t=1687187656; x=1689779656; h=content-transfer-encoding:cc:to:subject:message-id:date:from :in-reply-to:references:mime-version:from:to:cc:subject:date :message-id:reply-to; bh=V1P80GLbB1P+QCLo9sePDKKOVfDoXpG6ABk1BvxOeoo=; b=OngT6cRRJHc0AQ2pPOWCU/RshBXzk/4uDe5CNNOsC9EdEPtg/X+0G8OUcN55f/XTUc QKQRE185oFvR0YDjhcXcumkWRl911lzzJUDsrohK680Nz6ZTfcv3oKZAlyQOHlkWzTDj JOprueuu1AR8l4GPEMRoqbiQAAG9gtpAd51LrwkUzPdZH1vbrvAU6pT+qy3v/0DV2f1+ Rwt8yKFG4Er+blKbVjQOHosYB8Gu8XIxNS6VmjAdf6kfJjjVS9ASYMFr4Sk4W0ehpxNF 1gzHi5kBkyqIBtx7YDrBIw1qcTlN290/E3pQgHxGIbcdJsvbBn69lFLatPfbFh/Pf5qy JubQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1687187656; x=1689779656; h=content-transfer-encoding:cc:to:subject:message-id:date:from :in-reply-to:references:mime-version:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=V1P80GLbB1P+QCLo9sePDKKOVfDoXpG6ABk1BvxOeoo=; b=TtfEKPRRXPyd8F9qK4TbLjjU+xr/lieduc+LEKs9kpz/h6Y1ASS2MLihdJwY/8X1Mg K/kuQlKPMSm/yXEXTcIAMZErnSuI24GGPwFDd2TfeWkG6dJFtDp7fMX6esMtIMkqPQ70 UbH70qep4xiTosxiW5GPtA7yKCW0pmHP+u9KgptyDXUQ0wex1uanPmuHAXkr5AbRNUIX gT8nX0UyMRpkXMRv7vXhXIDhyG8vohu/P4BX+IbJXZRg9bwKP/keuzIyww0wNzLEvx17 SC6Q8BxbCZyq+Ebhpcz1vrCaWW5VbKvTlhsf7Yv8dST3p697SaUyGFWy4IdGt8+RLsFL uURw== X-Gm-Message-State: AC+VfDxeaQr6ak+kaCqj2D67zm5JKiP/6hiYXOGva5KhdRdYQ2ud9Udi NHsIaSxmUGeYzVD29b/4lL1LX65T+ZabJhwJSsCXGyze5p52YA== X-Google-Smtp-Source: ACHHUZ4DKh6yX4ASYKccIQRRx/fV31dTUfKzqZroN/Foytud5WTXHD18mC4Od6bkI1mNjar9SXHsW9k2rEUP37PAa/8= X-Received: by 2002:a25:e786:0:b0:b9e:b9b4:bb12 with SMTP id e128-20020a25e786000000b00b9eb9b4bb12mr6887466ybh.48.1687187655947; Mon, 19 Jun 2023 08:14:15 -0700 (PDT) MIME-Version: 1.0 References: In-Reply-To: From: Xiaofan Chen Date: Mon, 19 Jun 2023 23:14:04 +0800 Message-ID: Subject: Re: Clarification about the hidraw documentation on HIDIOCGFEATURE To: linux-input@vger.kernel.org Cc: Ihor Dutchak Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-input@vger.kernel.org On Mon, Jun 19, 2023 at 2:09=E2=80=AFPM Xiaofan Chen w= rote: > > 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 no= t > 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 =3D 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 usin= g > 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 --=20 Xiaofan