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=-12.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 1E0D9C433C1 for ; Tue, 30 Mar 2021 18:19:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CEAF2619CA for ; Tue, 30 Mar 2021 18:19:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232789AbhC3STF (ORCPT ); Tue, 30 Mar 2021 14:19:05 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39188 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232782AbhC3SSr (ORCPT ); Tue, 30 Mar 2021 14:18:47 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1C918C061574; Tue, 30 Mar 2021 11:18:47 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=Content-Transfer-Encoding:Content-Type: In-Reply-To:MIME-Version:Date:Message-ID:From:References:Cc:To:Subject:Sender :Reply-To:Content-ID:Content-Description; bh=KxGoy1weYbtqCANsJUAKQtRWb25OeKHfyfClNVXIBaM=; b=gbPTeAjgahdLzSFS7IrPEdFOWG +5DgazEYkC/GgEruOlW/Hbb6e82wb0caoCT3AxFssyjF98qFWKiaqxManyYPM2dKrDpGWwNxXO/Qk hUjY20ZPidsEh1h3xJL5VsWkBeAgdcJoLnUusm3Q+FPeBbgkxbhnJ5ZFeFzZk3F9VbCA9qEsXUIo8 R+dYBRK3ldbTMRybAOrQoddsWb16bNbRBLbS9oVSc/rrL0Sq50GzzFjCT1HoN7lozeociZMGq5RrK BiP/fYKQm0k6Hysxd/+KyJ6TavmJD53Iu+Xo41pytJEKdM4C+DvlknOTYKP8iMrskljP3gDJibM1L e/fz6THQ==; Received: from [2601:1c0:6280:3f0::4557] by casper.infradead.org with esmtpsa (Exim 4.94 #2 (Red Hat Linux)) id 1lRIwc-003QJf-5Y; Tue, 30 Mar 2021 18:18:35 +0000 Subject: Re: [PATCH RFC/RFT 1/1] misc: add simple logic analyzer using polling To: Wolfram Sang , linux-kernel@vger.kernel.org Cc: linux-renesas-soc@vger.kernel.org, linux-gpio@vger.kernel.org References: <20210330085655.12615-1-wsa+renesas@sang-engineering.com> <20210330085655.12615-2-wsa+renesas@sang-engineering.com> From: Randy Dunlap Message-ID: Date: Tue, 30 Mar 2021 11:18:23 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.0 MIME-Version: 1.0 In-Reply-To: <20210330085655.12615-2-wsa+renesas@sang-engineering.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-gpio@vger.kernel.org Hi-- On 3/30/21 1:56 AM, Wolfram Sang wrote: > diff --git a/Documentation/dev-tools/gpio-logic-analyzer.rst b/Documentation/dev-tools/gpio-logic-analyzer.rst > new file mode 100644 > index 000000000000..2847260736d4 > --- /dev/null > +++ b/Documentation/dev-tools/gpio-logic-analyzer.rst > @@ -0,0 +1,63 @@ > +Linux Kernel GPIO based logic analyzer > +====================================== > + > +:Author: Wolfram Sang > + > +Introduction > +------------ > + > +This document briefly describes how to run the software based in-kernel logic > +analyzer. > + > +Note that this is still a last resort analyzer which can be affected by > +latencies and non-determinant code paths. However, for e.g. remote development, > +it may be useful to get a first view and aid further debugging. > + > +Setup > +----- > + > +Tell the kernel which GPIOs are used as probes. For a DT based system: > + > + i2c-analyzer { > + compatible = "gpio-logic-analyzer"; > + probe-gpios = <&gpio6 21 GPIO_OPEN_DRAIN>, <&gpio6 4 GPIO_OPEN_DRAIN>; > + probe-names = "SCL", "SDA"; > + }; > + > +The binding documentation is in the ``misc`` folder of the Kernel binding > +documentation. > + > +Usage > +----- > + > +The logic analyzer is configurable via files in debugfs. However, it is > +strongly recommended to not use them directly, but to to use the > +``gpio-logic-analyzer`` script in the ``tools/debugging`` directory. Besides > +checking parameters more extensively, it will isolate a CPU core for you, so > +you will have least disturbance while measuring. > + > +The script has a help option explaining the parameters. For the above DT > +snipplet which analyzes an I2C bus at 400KHz on a Renesas Salvator-XS board, snippet > +the following settings are used: The isolated CPU shall be CPU1 because it is a > +big core in a big.LITTLE setup. Because CPU1 is the default, we don't need a > +parameter. The bus speed is 400kHz. So, the sampling theorem says we need to > +sample at least at 800kHz. However, falling of both, SDA and SCL, in a start Is "falling" like a falling edge of a signal? If not, then I think "failing" would make more sense. Even "failing both". > +condition is faster, so we need a higher sampling frequency, e.g. ``-s > +1500000`` for 1.5MHz. Also, we don't want to sample right away but wait for a > +start condition on an idle bus. So, we need to set a trigger to a falling edge > +on SDA, i.e. ``-t "2F"``. Last is the duration, let us assume 15ms here which > +results in the parameter ``-d 15000``. So, altogether: > + > + gpio-logic-analyzer -s 1500000 -t "2F" -d 15000 > + > +Note that the process will return you back to the prompt but a sub-process is > +still sampling in the background. Unless this finished, you will not find a > +result file in the current or specified directory. Please also note that > +currently this sub-process is not killable! For the above example, we will then > +need to trigger I2C communication: > + > + i2cdetect -y -r > + > +Result is a .sr file to be consumed with PulseView from the free Sigrok project. It is > +a zip file which also contains the binary sample data which may be consumed by others. > +The filename is the logic analyzer instance name plus a since-epoch timestamp. thanks. -- ~Randy