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=-14.0 required=3.0 tests=BAYES_00,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable 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 9B647C388F9 for ; Sat, 21 Nov 2020 12:56:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 683092224A for ; Sat, 21 Nov 2020 12:56:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727689AbgKUM4u (ORCPT ); Sat, 21 Nov 2020 07:56:50 -0500 Received: from mail-qk1-f196.google.com ([209.85.222.196]:45580 "EHLO mail-qk1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727668AbgKUM4t (ORCPT ); Sat, 21 Nov 2020 07:56:49 -0500 Received: by mail-qk1-f196.google.com with SMTP id q5so11695714qkc.12; Sat, 21 Nov 2020 04:56:48 -0800 (PST) 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; bh=ToElgtgxokI53Ol3P5lIooZ15Z39ALXjwMgyoo4gBOI=; b=la0bdU8k87RNC8aR3GUJLY41kxJD31M6iK9KEMVVC3GySneRUi4LSrkLewq/u2GRGm /x0EYXo/fO7EE4KW6rRwX/5xwmQbn3VVlqR3Fqq8hPSrZqLJpVX7/Ji4RbWPyuRd7c/E KmJxZjhvPIgY3rFaN6y8mWcMfE5oNPBxRhAPr5pC4meYr6atpHbX3jGcffC3JzGlTep6 7EDuR3L9FXyyvwDEnnYzVCkJHBGGeOWa2L2EWxdv6FFodzte+hj3JsjJrrE0M89ha7Ir 3E86kx8dHcrQ4X/E4x9z+S/eS9EszESDNly1ZBchUns+YdcUfQzbvuHKhhjeYRIYAAT8 Fyxw== X-Gm-Message-State: AOAM53393Mwvy1+tcLh8CjOE4ZP7EughqFRl/o4qNMN2K7Yg0b4n/wtB c8jXRawNzqR9TQCvHgkfnAAeOPXx7w== X-Google-Smtp-Source: ABdhPJw32SlJwXbb7W/+4G1tBXyRjdh05lyhTKZMeQ50JvIOaSn6aZJvBhb1cBsGLAX7x/7v1FPLIw== X-Received: by 2002:a37:a707:: with SMTP id q7mr1466240qke.5.1605963408068; Sat, 21 Nov 2020 04:56:48 -0800 (PST) Received: from xps15 ([2607:fb90:5feb:6270:cdf7:680e:59f2:6ccd]) by smtp.gmail.com with ESMTPSA id k4sm3903561qki.2.2020.11.21.04.56.43 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 21 Nov 2020 04:56:47 -0800 (PST) Received: (nullmailer pid 2083927 invoked by uid 1000); Sat, 21 Nov 2020 12:56:42 -0000 Date: Sat, 21 Nov 2020 06:56:42 -0600 From: Rob Herring To: Oleksij Rempel Cc: devicetree@vger.kernel.org, Rob Herring , Jonathan Cameron , Mark Brown , Krzysztof Kozlowski , linux-kernel@vger.kernel.org, kernel@pengutronix.de, linux-input@vger.kernel.org, Dmitry Torokhov , Benjamin Gaignard , David Jander Subject: Re: [PATCH v1] dt-bindings: touchscreen: add touchscreen-read-duration-us and touchscreen-settling-time-us properties Message-ID: <20201121125642.GA2083872@robh.at.kernel.org> References: <20201112112048.12134-1-o.rempel@pengutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20201112112048.12134-1-o.rempel@pengutronix.de> Precedence: bulk List-ID: X-Mailing-List: linux-input@vger.kernel.org On Thu, 12 Nov 2020 12:20:48 +0100, Oleksij Rempel wrote: > According to the TI application bulletin [1] we deal with two generic > mechanisms which would affect the precision of provided input events: > > |TOUCH SCREEN SETTLING TIME > | > |When the touch panel is pressed or touched, there are > |two mechanisms that will affect the voltage level at the contact point of > |the touch panel. These two mechanisms will cause the voltage across the > |touch panel to “ring” (oscillate), and then slowly settle (decay) > |down to a stable DC value. > | > |The two mechanisms are: > | 1) Mechanical bouncing caused by vibration of the top layer sheet of > | the touch panel when the panel is pressed. > | > | 2) Electrical ringing due to parasitic capacitance between the top > | and bottom layer sheets of the touch panel and at the input of ADS7843 > | that causes the voltage to “ring”(oscillate). > > Since both of this mechanisms are board specific and reflect the > mechanical, and electrical properties of end product, it is better to > provide a generic properties to address them. > > The touchscreen-read-duration-us property should address 1. mechanism. > This effect can be triggered by device specific design. The duration ma be > dependent on the use case of the end device. For example a touch where > writing is required may have other timing requirements as the device > where only "buttons" should be pressed. > > The touchscreen-settling-time-us property should address 2. mechanism > where the size and construction of touch screen plates affect the parasitic > capacitance and time needed between enabling power supply for the > plates, and actual usable voltage level to detect the position of touch event. > > [1] https://www.ti.com/lit/an/sbaa036/sbaa036.pdf > > Signed-off-by: Oleksij Rempel > --- > .../bindings/input/touchscreen/touchscreen.yaml | 9 +++++++++ > 1 file changed, 9 insertions(+) > Reviewed-by: Rob Herring