From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932413AbcFIWQE (ORCPT ); Thu, 9 Jun 2016 18:16:04 -0400 Received: from youngberry.canonical.com ([91.189.89.112]:50646 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932219AbcFIVRf (ORCPT ); Thu, 9 Jun 2016 17:17:35 -0400 From: Kamal Mostafa To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, kernel-team@lists.ubuntu.com Cc: Akshay Bhat , Guenter Roeck , Kamal Mostafa Subject: [PATCH 4.2.y-ckt 023/206] hwmon: (ads7828) Enable internal reference Date: Thu, 9 Jun 2016 14:13:52 -0700 Message-Id: <1465507015-23052-24-git-send-email-kamal@canonical.com> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1465507015-23052-1-git-send-email-kamal@canonical.com> References: <1465507015-23052-1-git-send-email-kamal@canonical.com> X-Extended-Stable: 4.2 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 4.2.8-ckt12 -stable review patch. If anyone has any objections, please let me know. ---8<------------------------------------------------------------ From: Akshay Bhat commit 7a18afe8097731b8ffb6cb5b2b3b418ded77c105 upstream. On ads7828 the internal reference defaults to off upon power up. When using internal reference, it needs to be turned on and the voltage needs to settle before normal conversion cycle can be started. Hence perform a dummy read in the probe to enable the internal reference allowing the voltage to settle before performing a normal read. Without this fix, the first read from the ADC when using internal reference always returns incorrect data. Signed-off-by: Akshay Bhat Signed-off-by: Guenter Roeck Signed-off-by: Kamal Mostafa --- drivers/hwmon/ads7828.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/drivers/hwmon/ads7828.c b/drivers/hwmon/ads7828.c index 6c99ee7..ee396ff 100644 --- a/drivers/hwmon/ads7828.c +++ b/drivers/hwmon/ads7828.c @@ -120,6 +120,7 @@ static int ads7828_probe(struct i2c_client *client, unsigned int vref_mv = ADS7828_INT_VREF_MV; bool diff_input = false; bool ext_vref = false; + unsigned int regval; data = devm_kzalloc(dev, sizeof(struct ads7828_data), GFP_KERNEL); if (!data) @@ -154,6 +155,15 @@ static int ads7828_probe(struct i2c_client *client, if (!diff_input) data->cmd_byte |= ADS7828_CMD_SD_SE; + /* + * Datasheet specifies internal reference voltage is disabled by + * default. The internal reference voltage needs to be enabled and + * voltage needs to settle before getting valid ADC data. So perform a + * dummy read to enable the internal reference voltage. + */ + if (!ext_vref) + regmap_read(data->regmap, data->cmd_byte, ®val); + hwmon_dev = devm_hwmon_device_register_with_groups(dev, client->name, data, ads7828_groups); -- 2.7.4