From patchwork Sat Jun 23 18:54:47 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Andreas Klinger X-Patchwork-Id: 10483823 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 365EE6023A for ; Sat, 23 Jun 2018 18:55:44 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 1F28F2880D for ; Sat, 23 Jun 2018 18:55:44 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 1241328A0F; Sat, 23 Jun 2018 18:55:44 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.9 required=2.0 tests=BAYES_00, MAILING_LIST_MULTI, RCVD_IN_DNSWL_HI autolearn=unavailable version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id BB6622880D for ; Sat, 23 Jun 2018 18:55:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751803AbeFWSzb (ORCPT ); Sat, 23 Jun 2018 14:55:31 -0400 Received: from mout.kundenserver.de ([212.227.17.10]:55105 "EHLO mout.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751724AbeFWSza (ORCPT ); Sat, 23 Jun 2018 14:55:30 -0400 Received: from localhost ([2.166.249.57]) by mrelayeu.kundenserver.de (mreue102 [212.227.15.183]) with ESMTPSA (Nemesis) id 0LfznH-1fz0c62wOJ-00pfjb; Sat, 23 Jun 2018 20:54:49 +0200 Date: Sat, 23 Jun 2018 20:54:47 +0200 From: Andreas Klinger To: jic23@kernel.org, knaack.h@gmx.de, lars@metafoo.de, pmeerw@pmeerw.net, robh+dt@kernel.org, mark.rutland@arm.com, mchehab@kernel.org, davem@davemloft.net, gregkh@linuxfoundation.org, akpm@linux-foundation.org, linus.walleij@linaro.org, rdunlap@infradead.org, devicetree@vger.kernel.org, linux-iio@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH 2/3] iio: hx711: add delay until DOUT is ready Message-ID: <20180623185447.GA17853@arbeit> MIME-Version: 1.0 Content-Disposition: inline User-Agent: Mutt/1.5.23 (2014-03-12) X-Provags-ID: V03:K1:wAzWFPnfRIcMxVuJLQf8WStkDbM2MxKpUVyVweA7btQbDE8PSv2 cOrPSd0bKNHyXaxNSn7Dm4jDydCDPQvO6T9VaIlUL0Bt1Zn/WW9geXp5gmdJnBKzy6BRYqw N8yR7Mj+hhZlWI7NLXPgGv5hUFOSGvV6Pj2Gd8+rBdzXd4ypUAHnMWC42PvpflUklubpTA8 +FbracugSt3ZfS1jig7kw== X-UI-Out-Filterresults: notjunk:1; V01:K0:h2+igRNAk1w=:OvTKIZxhXYVMQNHqU2zdBn 3n/HurMKTgzK2l53CGrZ7iRajiV8JZ1azl875YZLIabRsrn3SImzheSfx7Y8ASeJV1z98S5cd vYNvdEbMOql0Y/NknAMOLXqsJxBBJ1C5pJ9n6D5tQR+gpU64W8zRJ+THdzlOnWvfHvrnQG36Z w5zAHuhAMTyNuriQObflfE048LuG6sUuHg/4NXI8QA0Sm8f7Ll9iFJiYJ9NmtvQJdQ3VQS6A8 Is/OenXBJxN1mWN6sCKFTSVtcCTlMLLnoS+swZhPEnrNMAql2r9/TJMK85GmR0Ay5U0XhgQMH HoP1JmKpGMcKKpNcbWLlZo0mIOfGGMpEk3YTk6/W99jX8/WKOLipuyxvpZmKKt+BPHxw5MPjN wCZ+ghAWgCZseUUEAQDfx0hx0HOn5R0QzFoEWB9C7hMBegQUpKTWE1L49atJI3HzdCAKHUMa1 QSCdh3ihRICsC7+VhyZ1TLOW6mrhNCZZeuM58oPlivTCgNEli34v/6TTUZSF2aHwwCqm4/zmq 0SWoUVuUqH8WwvVu3VAGPnnjbZYyWfoL4LonuYQL6S1OHTucaBt0l2dPlq2O58nWe01VRde01 9cUBjygKBEhV8b3pilS6XpNhwkuWo/73AXrKoKj7JAE5QO6eU9UhOhpHlvP38KvRkKcvkpkl4 zqqznS7w7NqTggWcgMWqJXqzNeNoEXR13nUastBr8H8QsUW9hO1QZmBkpGu46Sc1niSg= Sender: linux-iio-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-iio@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP On a system with parasitic capacities it turned out that DOUT is not ready after 100 ns after PD_SCK has raised. A measurement showed almost 1000 ns until DOUT has reached its correct value. With this patch its now possible to wait until data is ready. The wait time should not be higher than the maximum PD_SCK high time which is corresponding to the datasheet 50000 ns. Signed-off-by: Andreas Klinger --- drivers/iio/adc/hx711.c | 23 +++++++++++++++++++++++ 1 file changed, 23 insertions(+) diff --git a/drivers/iio/adc/hx711.c b/drivers/iio/adc/hx711.c index 9430b54121e0..41e26ef324ee 100644 --- a/drivers/iio/adc/hx711.c +++ b/drivers/iio/adc/hx711.c @@ -97,6 +97,13 @@ struct hx711_data { * 2x32-bit channel + 64-bit timestamp */ u32 buffer[4]; + /* + * delay after a rising edge on SCK until the data is ready DOUT + * this is dependent on the hx711 where the datasheet tells a + * maximum value of 100 ns + * but also on potential parasitic capacities on the wiring + */ + u32 data_ready_delay_ns; }; static int hx711_cycle(struct hx711_data *hx711_data) @@ -110,6 +117,14 @@ static int hx711_cycle(struct hx711_data *hx711_data) */ preempt_disable(); gpiod_set_value(hx711_data->gpiod_pd_sck, 1); + + /* + * wait until DOUT is ready + * it turned out that parasitic capacities are extending the time + * until DOUT has reached it's value + */ + ndelay(hx711_data->data_ready_delay_ns); + val = gpiod_get_value(hx711_data->gpiod_dout); /* * here we are not waiting for 0.2 us as suggested by the datasheet, @@ -458,6 +473,7 @@ static const struct iio_chan_spec hx711_chan_spec[] = { static int hx711_probe(struct platform_device *pdev) { struct device *dev = &pdev->dev; + struct device_node *np = dev->of_node; struct hx711_data *hx711_data; struct iio_dev *indio_dev; int ret; @@ -530,6 +546,13 @@ static int hx711_probe(struct platform_device *pdev) hx711_data->gain_set = 128; hx711_data->gain_chan_a = 128; + ret = of_property_read_u32(np, "data-ready-delay-ns", + &hx711_data->data_ready_delay_ns); + if (ret < 0) { + dev_warn(dev, "data-ready-delay-ns not set - assuming 0 ns\n"); + hx711_data->data_ready_delay_ns = 0; + } + platform_set_drvdata(pdev, indio_dev); indio_dev->name = "hx711";