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 X-Spam-Level: X-Spam-Status: No, score=-7.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4E303C2D0CE for ; Tue, 21 Jan 2020 21:34:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2310E20882 for ; Tue, 21 Jan 2020 21:34:47 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="PyG5fCa9" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729157AbgAUVeq (ORCPT ); Tue, 21 Jan 2020 16:34:46 -0500 Received: from mail-pg1-f174.google.com ([209.85.215.174]:33623 "EHLO mail-pg1-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728827AbgAUVep (ORCPT ); Tue, 21 Jan 2020 16:34:45 -0500 Received: by mail-pg1-f174.google.com with SMTP id 6so2235555pgk.0 for ; Tue, 21 Jan 2020 13:34:44 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:content-transfer-encoding:in-reply-to :user-agent; bh=I18DxLC+IvKxsXR/JuvN1uuByhHfT+oS5l19yxEjbms=; b=PyG5fCa9gvz3spmoOJefdYK+DCdpTdmSlhMj9lu7nABkWjhZXK+kSo+skjEHyzCLn0 eFYyhkd+DYru06tdYnHj+pt5XMf/7jGpleo5/3yMS5oi5MDIFPwrrrAaQvsM2aJBGQjq l6DZiVBI6behPqA8We1hCTX2vE6URWaasLzDTycH/fyBKsc9CC3aAVYBiuECPF/+WR5t 3NUcu/ppjN9hGIfrV49c60H3ZMsqkh0UgUj+qw2SwY1VC5KJMXkvEGCy7TXkNKM4ate8 5kOWSwc81CElNjIxiEX2dOvgYyJYhgF1A4AukjnC3W4m541jZZthtl3YJbvDoju/0zOv jRxA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:content-transfer-encoding :in-reply-to:user-agent; bh=I18DxLC+IvKxsXR/JuvN1uuByhHfT+oS5l19yxEjbms=; b=Xy7OUyoWEa98rUhVkyUg2S2VaQlQob9cucCkKhngEbolZky3qJ19gVu2m9C0ii7ysA vpB5+4ElbfbbRCW7FR09AUWp5kGTm6VrAVWn2TY9Kz+W6vQD8+L4S+7dLelyFNVZRmls uq5AVoszK1XVQhY+0cDyqWtLCspBVm7eky9GSaUPNtQPZZ8E70gL4Dg9T5KpOA/gapg8 KsGjqxhr9OdF18ZA0tMDI4F0yztjD+8gPmd8Tl3YUKd4tFsYgCgM45GzvEcyvo6bmo63 Jvz3KFDL9a3rqF2gxK2lm3jlZ7jPo0jtUKQArLHCnG4Zujg72fq8wQv9MQAXQHHTx07+ n6jg== X-Gm-Message-State: APjAAAX5Fwr4wLSlhEQlZdW0UAMcRJywwR6hpjqI2Gdn1db8uelyQRKi c2BH2S9GjLJwCOl58olaouk= X-Google-Smtp-Source: APXvYqxo+M/Le0MUnaolOuqGuh2LbT69O1wxF5c5yDI/JuZsM2hCl3U247l08yO1xFzru10RV4N3zQ== X-Received: by 2002:a63:4a50:: with SMTP id j16mr4232223pgl.323.1579642484112; Tue, 21 Jan 2020 13:34:44 -0800 (PST) Received: from dtor-ws ([2620:15c:202:201:3adc:b08c:7acc:b325]) by smtp.gmail.com with ESMTPSA id c18sm43951403pfr.40.2020.01.21.13.34.43 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 21 Jan 2020 13:34:43 -0800 (PST) Date: Tue, 21 Jan 2020 13:34:41 -0800 From: "dmitry.torokhov@gmail.com" To: Pali =?iso-8859-1?Q?Roh=E1r?= Cc: "Leutwein Tobias (BEG/ENC1)" , "linux-input@vger.kernel.org" , Peter Hutterer Subject: Re: [RFC] linux-input alps - loosing precision Message-ID: <20200121213441.GO47797@dtor-ws> References: <988f2b799a6046af87a25c996ebbfacb@de.bosch.com> <20200117094206.xu47p6ybxmsf5ne2@pali> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20200117094206.xu47p6ybxmsf5ne2@pali> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-input-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-input@vger.kernel.org Hi Pali, On Fri, Jan 17, 2020 at 10:42:06AM +0100, Pali Rohár wrote: > On Thursday 09 January 2020 14:26:16 Leutwein Tobias (BEG/ENC1) wrote: > > Hello, > > > > At the file > > https://github.com/torvalds/linux/blob/master/drivers/input/mouse/alps.c > > I've seen that values coming from the trackpoint/trackstick are divided at some devices, which results in a loss of precision. > > > > As I was not lucky with the behavior of the trackpoint of my computer I've made a fork of libinput https://gitlab.freedesktop.org/leutwe/libinput/tree/master/ > > where I changed src/filter-trackpoint.c . With this change, the values from lib evdev are multiplied by a factor (dpToFac_au16 []). The array element used from dpToFac_au16 [] is also the value received by evdev. > > > > At higher forces I use a factor much higher than 1, so the undivided value from the device would be the best for me. > > > > In order not to change the behavior for other users, it might be possible to change the divider at runtime via the sys- file system - like it is at trackpoint.c and take the currently used divider as default value. > > > > Positions at source code were I see the division: > > > > alps_process_trackstick_packet_v3() > > /* > > * The x and y values tend to be quite large, and when used > > * alone the trackstick is difficult to use. Scale them down > > * to compensate. > > */ > > x /= 8; > > y /= 8; > > > > alps_process_packet_v6() > > /* Divide 4 since trackpoint's speed is too fast */ input_report_rel(dev2, REL_X, (char)x / 4); input_report_rel(dev2, REL_Y, -((char)y / 4)); > > Hello Dmitry! > > This problem is about fact that alps.c for some ALPS devices already > truncate precision of trackpoint movement. > > Tobias is unhappy with this fact and would like to get all bits of > movement information, not just some high. > > But existing userspace application expects that for these devices kernel > already truncate precision and process truncated data from kernel. > > Now question is: Are we able to send to userspace input data without > doing truncation and without breaking existing applications? > > It looks like that for such thing we need some userspace <--> kernel API > which disable truncating of precision. > > Have you been solving similar issue for other other drivers or in other > area of input code? Unfortunately I do not think we can automatically "recover" the lost precision without help of libinput, which would need to tweak the trackpoint [sysfs] property letting kernel know that it should send original data. I'm adding Peter to hear his take on this. Thanks. -- Dmitry