From patchwork Mon Dec 3 08:01:18 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Vignesh Raghavendra X-Patchwork-Id: 10708717 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id B122B13BF for ; Mon, 3 Dec 2018 08:01:24 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id A62CB29289 for ; Mon, 3 Dec 2018 08:01:24 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id A37E12ADC7; Mon, 3 Dec 2018 08:01:24 +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=-8.0 required=2.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI autolearn=ham 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 1D3912ADA8 for ; Mon, 3 Dec 2018 08:01:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725908AbeLCIBP (ORCPT ); Mon, 3 Dec 2018 03:01:15 -0500 Received: from fllv0015.ext.ti.com ([198.47.19.141]:42670 "EHLO fllv0015.ext.ti.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725835AbeLCIBP (ORCPT ); Mon, 3 Dec 2018 03:01:15 -0500 Received: from fllv0035.itg.ti.com ([10.64.41.0]) by fllv0015.ext.ti.com (8.15.2/8.15.2) with ESMTP id wB380lU0103284; Mon, 3 Dec 2018 02:00:47 -0600 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ti.com; s=ti-com-17Q1; t=1543824047; bh=ki3wadxapcwwi7aaamt7L3VIEtYjf1ugmOR0RksSZZA=; h=From:To:CC:Subject:Date:In-Reply-To:References; b=eJ8f25CZGSRS5aHsS5LwVyocz/xcGvoTzMNkGjJmDd8258iQhjs9xNCBw/SKSzNmC 1aufxDvoYFvsR8AsT/8MdU3ACH/miHatp/Yh+VDwUQHYV4REve2VuABkHZw90qJdyJ vUOQ8xO5c3DUUIKygbeWRXBf5KpdLLr3wls1H3vw= Received: from DFLE108.ent.ti.com (dfle108.ent.ti.com [10.64.6.29]) by fllv0035.itg.ti.com (8.15.2/8.15.2) with ESMTPS id wB380lN2119867 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=FAIL); Mon, 3 Dec 2018 02:00:47 -0600 Received: from DFLE115.ent.ti.com (10.64.6.36) by DFLE108.ent.ti.com (10.64.6.29) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P256) id 15.1.1591.10; Mon, 3 Dec 2018 02:00:46 -0600 Received: from dlep32.itg.ti.com (157.170.170.100) by DFLE115.ent.ti.com (10.64.6.36) with Microsoft SMTP Server (version=TLS1_0, cipher=TLS_RSA_WITH_AES_256_CBC_SHA) id 15.1.1591.10 via Frontend Transport; Mon, 3 Dec 2018 02:00:46 -0600 Received: from a0132425.india.ti.com (ileax41-snat.itg.ti.com [10.172.224.153]) by dlep32.itg.ti.com (8.14.3/8.13.8) with ESMTP id wB380bfb024335; Mon, 3 Dec 2018 02:00:44 -0600 From: Vignesh R To: Lee Jones CC: Jonathan Cameron , Hartmut Knaack , Lars-Peter Clausen , Peter Meerwald-Stadler , Vignesh R , , , Subject: [PATCH v2 2/2] iio: adc: ti_am335x_tscadc: Improve accuracy of measurement Date: Mon, 3 Dec 2018 13:31:18 +0530 Message-ID: <20181203080118.17504-3-vigneshr@ti.com> X-Mailer: git-send-email 2.19.2 In-Reply-To: <20181203080118.17504-1-vigneshr@ti.com> References: <20181203080118.17504-1-vigneshr@ti.com> MIME-Version: 1.0 X-EXCLAIMER-MD-CONFIG: e1e8a2fd-e40a-4ac6-ac9b-f7e9cc9ee180 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 When performing single ended measurements with TSCADC, its recommended to set negative input (SEL_INM_SWC_3_0) of ADC step to ADC's VREFN in the corresponding STEP_CONFIGx register. Also, the positive(SEL_RFP_SWC_2_0) and negative(SEL_RFM_SWC_1_0) reference voltage for ADC step needs to be set to VREFP and VREFN respectively in STEP_CONFIGx register. Without these changes, there may be variation of as much as ~2% in the ADC's digital output which is bad for precise measurement. Signed-off-by: Vignesh R Acked-by: Jonathan Cameron Acked-by: Lee Jones --- v2: No change drivers/iio/adc/ti_am335x_adc.c | 5 ++++- include/linux/mfd/ti_am335x_tscadc.h | 4 ++++ 2 files changed, 8 insertions(+), 1 deletion(-) diff --git a/drivers/iio/adc/ti_am335x_adc.c b/drivers/iio/adc/ti_am335x_adc.c index cafb1dcadc48..9d984f2a8ba7 100644 --- a/drivers/iio/adc/ti_am335x_adc.c +++ b/drivers/iio/adc/ti_am335x_adc.c @@ -142,7 +142,10 @@ static void tiadc_step_config(struct iio_dev *indio_dev) stepconfig |= STEPCONFIG_MODE_SWCNT; tiadc_writel(adc_dev, REG_STEPCONFIG(steps), - stepconfig | STEPCONFIG_INP(chan)); + stepconfig | STEPCONFIG_INP(chan) | + STEPCONFIG_INM_ADCREFM | + STEPCONFIG_RFP_VREFP | + STEPCONFIG_RFM_VREFN); if (adc_dev->open_delay[i] > STEPDELAY_OPEN_MASK) { dev_warn(dev, "chan %d open delay truncating to 0x3FFFF\n", diff --git a/include/linux/mfd/ti_am335x_tscadc.h b/include/linux/mfd/ti_am335x_tscadc.h index b9a53e013bff..483168403ae5 100644 --- a/include/linux/mfd/ti_am335x_tscadc.h +++ b/include/linux/mfd/ti_am335x_tscadc.h @@ -78,6 +78,8 @@ #define STEPCONFIG_YNN BIT(8) #define STEPCONFIG_XNP BIT(9) #define STEPCONFIG_YPN BIT(10) +#define STEPCONFIG_RFP(val) ((val) << 12) +#define STEPCONFIG_RFP_VREFP (0x3 << 12) #define STEPCONFIG_INM_MASK (0xF << 15) #define STEPCONFIG_INM(val) ((val) << 15) #define STEPCONFIG_INM_ADCREFM STEPCONFIG_INM(8) @@ -86,6 +88,8 @@ #define STEPCONFIG_INP_AN4 STEPCONFIG_INP(4) #define STEPCONFIG_INP_ADCREFM STEPCONFIG_INP(8) #define STEPCONFIG_FIFO1 BIT(26) +#define STEPCONFIG_RFM(val) ((val) << 23) +#define STEPCONFIG_RFM_VREFN (0x3 << 23) /* Delay register */ #define STEPDELAY_OPEN_MASK (0x3FFFF << 0)