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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0E082C4332F for ; Sat, 12 Nov 2022 17:20:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235025AbiKLRUP (ORCPT ); Sat, 12 Nov 2022 12:20:15 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59212 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230257AbiKLRUN (ORCPT ); Sat, 12 Nov 2022 12:20:13 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A9C6010B6A; Sat, 12 Nov 2022 09:20:12 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 6D8D0B80989; Sat, 12 Nov 2022 17:20:11 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 19B0DC433C1; Sat, 12 Nov 2022 17:20:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1668273610; bh=TBYplVtCLdDavccVW3miYQQ5hU7uovgIup9ciXBlwmo=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=PEDLeSqRLCqZBwWSwQbWjY57dDnv2P5O2zfbc7+w51XkZf/PeTFGX467BpZN3jdnG /SPAoXPeLXH7R/3Yails/aHJ+FtJPZCgIoBUTfg0cVFG4kVCkJygTNmsG5qrjre+t8 FzYLuKqof8N0RQ+9EYkcMpY+5JVIN0gOhzBmzhqSgsoFyvtnfs6rH9mqtIsW0F2jU3 dg5vhdaDcWxB/mpEiRr5phj83Lmcwkt2/lE/booFVgBQqhGOhyj9Vh2z7ecCYY+Rnl J9JI+GqqKgLV9AxL5uKldyUTcHk0siEnmpVzpRqaUeMsSgZyayS3qZ1VDUkiKqKU+z EvmfYaAfbVwTw== Date: Sat, 12 Nov 2022 17:32:22 +0000 From: Jonathan Cameron To: Mitja Spes Cc: Lars-Peter Clausen , Angelo Compagnucci , linux-iio@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 3/4] iio: adc: mcp3422: add hardware gain attribute Message-ID: <20221112173222.0ca56017@jic23-huawei> In-Reply-To: <20221111112657.1521307-4-mitja@lxnav.com> References: <20221111112657.1521307-1-mitja@lxnav.com> <20221111112657.1521307-4-mitja@lxnav.com> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.34; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 11 Nov 2022 12:26:55 +0100 Mitja Spes wrote: > Allows setting gain separately from scale. How are the separate? We normally only use hardwaregain if changing it has no input on the scale that we need to apply in userspace to raw channels. This normally happens for two reasons 1) There is a micro controller on the sensor that is doing a bunch of maths so whilst changing the PGA value changes the range measurable it doesn't affect the representation when we read from the device. 2) The hardware gain is controlling say the sensitivity of a light sensor in a time of flight device - it affects if we can get a measurement, but not the measurement itself. Any of that true here? If not, we shouldn't be adding a hardwaregain attribute - which is why almost no ADCs have them... Jonathan > > Signed-off-by: Mitja Spes > --- > drivers/iio/adc/mcp3422.c | 32 +++++++++++++++++++++++++++++++- > 1 file changed, 31 insertions(+), 1 deletion(-) > > diff --git a/drivers/iio/adc/mcp3422.c b/drivers/iio/adc/mcp3422.c > index cfb629b964af..eef35fb2fc22 100644 > --- a/drivers/iio/adc/mcp3422.c > +++ b/drivers/iio/adc/mcp3422.c > @@ -58,7 +58,8 @@ > .channel = _index, \ > .info_mask_separate = BIT(IIO_CHAN_INFO_RAW) \ > | BIT(IIO_CHAN_INFO_SCALE) \ > - | BIT(IIO_CHAN_INFO_SAMP_FREQ), \ > + | BIT(IIO_CHAN_INFO_SAMP_FREQ) \ > + | BIT(IIO_CHAN_INFO_HARDWAREGAIN), \ > } > > static const int mcp3422_scales[MCP3422_SRATE_COUNT][MCP3422_PGA_COUNT] = { > @@ -184,6 +185,10 @@ static int mcp3422_read_raw(struct iio_dev *iio, > *val1 = mcp3422_sample_rates[sample_rate]; > return IIO_VAL_INT; > > + case IIO_CHAN_INFO_HARDWAREGAIN: > + *val1 = (1 << pga); > + return IIO_VAL_INT; > + > default: > break; > } > @@ -245,6 +250,29 @@ static int mcp3422_write_raw(struct iio_dev *iio, > adc->ch_config[req_channel] = config; > return 0; > > + case IIO_CHAN_INFO_HARDWAREGAIN: > + switch (val1) { > + case 1: > + temp = MCP3422_PGA_1; > + break; > + case 2: > + temp = MCP3422_PGA_2; > + break; > + case 4: > + temp = MCP3422_PGA_4; > + break; > + case 8: > + temp = MCP3422_PGA_8; > + break; > + default: > + return -EINVAL; > + } > + > + config &= ~MCP3422_PGA_MASK; > + config |= MCP3422_PGA_VALUE(temp); > + adc->ch_config[req_channel] = config; > + return 0; > + > default: > break; > } > @@ -260,6 +288,8 @@ static int mcp3422_write_raw_get_fmt(struct iio_dev *indio_dev, > return IIO_VAL_INT_PLUS_NANO; > case IIO_CHAN_INFO_SAMP_FREQ: > return IIO_VAL_INT_PLUS_MICRO; > + case IIO_CHAN_INFO_HARDWAREGAIN: > + return IIO_VAL_INT_PLUS_MICRO; > default: > return -EINVAL; > }