From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pf1-f181.google.com (mail-pf1-f181.google.com [209.85.210.181]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id DACAC26E709 for ; Fri, 27 Mar 2026 06:17:56 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.210.181 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774592278; cv=none; b=fnHKgbmEPY3hC1FdgQq43XAyE94FyYafNg68w9Mjdnv7ir/oy+m5m9s7UaFSCuWifP3kycQH8CV7/ggSSOtx55p+QXrQKAYLcpxzYZTKSWmVYUJesRkZTdoeDCLY3nMOYQ88vjWnfNXLc4Wvzr8nnYaQyxD4OTGMTltzZYV1QhA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774592278; c=relaxed/simple; bh=vlRO8fz3Y7Z3gjxTFYHc1jOH0ZEVel8srKDBPj48td8=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=rdiknITAD2XuuNgHw7g5dRNkbshM6DZme2zWU6dS5tFv7mhMkWDcNrG+xTOuh/vS3aymspc+nDGOurIh9pNgmAOq3oB0W4MpkT4uurD2YRxY8cCwO/aYd2n2dzhjuCyvIAlMr719vSBoO3XyN0Am0iJYFsed0RMxymrHeAHk5eg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=Dv3URdG3; arc=none smtp.client-ip=209.85.210.181 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="Dv3URdG3" Received: by mail-pf1-f181.google.com with SMTP id d2e1a72fcca58-82a67ce6969so1337809b3a.1 for ; Thu, 26 Mar 2026 23:17:56 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1774592276; x=1775197076; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=Ay9PCtGNQoL7LOWqeEaI1OzTCaO/93pal7QlVNlPYo4=; b=Dv3URdG3h7rgDAqlEKrJw38EqBt17qhsXEZwylKvDMS6GLJ45xeO2vo4mypZZr4du4 oRkRC0zUrW73zTbxA5pLF1yQzmzLjiL8Kcmk1Lv+gxbQm8ajoXU978kCDtJ16G/fJJXE qtIjmW67OnfQ4CzGru1+Nyv0P4ui8Z+wkLQgnko5gz51Ueq2gwk1XO+JZkV3KHEE0rmQ sqNA2HwZW/l+BGfLC8/8hxU9L3wyVOY8dMNM48YM3ROJHSIcdvX7B3MmiOJUV8TKJL37 i5imttApJgVLBIgdEVD6Fd2AnR2gfOrucmseszH56XGFrVWXy0ZEqYCe0welCVFEPICm gszg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1774592276; x=1775197076; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-gg:x-gm-message-state:from :to:cc:subject:date:message-id:reply-to; bh=Ay9PCtGNQoL7LOWqeEaI1OzTCaO/93pal7QlVNlPYo4=; b=IxLtzIeesV/vVNlfbKsKjucIZrU6sN/+HAjmGBwCd661NvV/Grzpo885vHZdSr9Ene h4C9GR309nH0WFDUzwgWHfkp09CT53dvIFEBs2w3XIxS/hAWUZApayjEjZLM0BfO2vV0 cbjOWnY/w3rx9UEyNCtSl1ZZZs2XuUtQ2xe6W8yGrIv1GJzevlRfj8yHYfv80yyekFun XpnqOcn/g2F5pFEcwaqSHy+uLYhZorO44p72w4ay9nzveYyGf+VFCG/mhKEswKsYB+A1 P19Xfb9gpNTIsc0+QjDVoS1MzUKPmzKM9kmn/l6BI9J7ZAhlHnWtLjIW6MuNgweldglM 3KWw== X-Forwarded-Encrypted: i=1; AJvYcCW3aRILaeeQUgUTQ62yfaWdN84v/X1gX96RmkPyIKEtayB89Mb8VVUYcahsw3ohhKhQBWTUiYSWM6s=@vger.kernel.org X-Gm-Message-State: AOJu0YxvuM/xaxzmZIW3CmWcu3holAyh+JiyIW+i29KwEoRnAytHhOpW vKO/OUlyS3xkRqjnHsBu97NAi+cpzynKgUqyjlnrqoYuZ/voDDDbEL0phsfLaktPjM1D X-Gm-Gg: ATEYQzxOTecEU+8cGbxCLwUoe0IKSMpEY0pNb01jyLTTz5WKNV+HmWDjfavdnKEZtYu qU5vGgSqBMmn+3VpBP4csC5rv9xf/jXv1Jz1T/1aJSI3CiMLGR/harm+LBzDSHBhp2n6a2flm7o itUC/ft8BT+YWgz4K2HGGM0deyhIZ72hM8EPVIOC1hm35fReZMytwKe/RzrOdwPzcKT6tU2GyAI CxkoCXiz3VPeRU7kMP7Kc8CGjEUZ1esrCCpLoNtDVRpJ4m4ob0TwUFACWjumT+UEjggCaq1hhAQ lhGTCRU/D5VhG124g2Bw2OkKJtiWCTrBBEsQWooh2M+KUar4/Or453KKqID+gA0jxSiRmnIUryF YRG7ThqeXFZNf5MaIRKFr7BSCxTsJXYz1YQjf7nH54JH+Rw6o9fDxg2DApGZCL/H/wgwxmpAZFy XujhoZmT+cMq+A8/RiwsI505BGLkS5EPckM/O4N2RfPCy7O3cv8Zn3TE0uT/n7k6Z8YNOmPTowk zOhbyaSefqut+FZByL1gFtTbXixEaiJnYELsEonywJ1lUI3ZUSK5Bgb X-Received: by 2002:a05:6a00:3486:b0:829:7d31:dd9a with SMTP id d2e1a72fcca58-82c96002073mr1322389b3a.51.1774592276142; Thu, 26 Mar 2026 23:17:56 -0700 (PDT) Received: from nik.wlan.qualcomm.com (blr-bdr-fw-01_GlobalNAT_AllZones-Outside.qualcomm.com. [103.229.18.19]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-82c7d3f76e3sm4569546b3a.52.2026.03.26.23.17.53 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 26 Mar 2026 23:17:55 -0700 (PDT) From: Nikhil Gautam To: jic23@kernel.org Cc: anshulusr@gmail.com, dlechner@baylibre.com, linux-iio@vger.kernel.org, Nikhil Gautam Subject: [PATCH v3] iio: dac: mcp4821: add configurable gain support Date: Fri, 27 Mar 2026 11:48:02 +0530 Message-ID: <20260327061802.13043-1-nikhilgtr@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-iio@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Add support for configuring the DAC gain using the GA bit. Expose gain control via IIO_CHAN_INFO_CALIBSCALE. Scale is updated dynamically based on selected gain: - 1x gain → 2.048V full-scale - 2x gain → 4.096V full-scale Signed-off-by: Nikhil Gautam --- Changes in v2: - Drop header reordering - Move MCP4821_GAIN_ENABLE define before MCP4802_SECOND_CHAN - Use IIO_CHAN_INFO_SCALE instead of CALIBSCALE since full scale changes - Restore original -EINVAL handling in default cases Changes in v3: - Restored NULL check in indio_dev alloc --- drivers/iio/dac/mcp4821.c | 103 ++++++++++++++++++++++++++++++-------- 1 file changed, 82 insertions(+), 21 deletions(-) diff --git a/drivers/iio/dac/mcp4821.c b/drivers/iio/dac/mcp4821.c index 748bdca9a964..9160812219f9 100644 --- a/drivers/iio/dac/mcp4821.c +++ b/drivers/iio/dac/mcp4821.c @@ -12,7 +12,6 @@ * MCP48x2: https://ww1.microchip.com/downloads/en/DeviceDoc/20002249B.pdf * * TODO: - * - Configurable gain * - Regulator control */ @@ -26,12 +25,32 @@ #include #define MCP4821_ACTIVE_MODE BIT(12) +#define MCP4821_GAIN_ENABLE BIT(13) #define MCP4802_SECOND_CHAN BIT(15) -/* DAC uses an internal Voltage reference of 4.096V at a gain of 2x */ -#define MCP4821_2X_GAIN_VREF_MV 4096 +/* DAC uses an internal Voltage reference of 2.048V */ +#define MCP4821_VREF_MV 2048 -enum mcp4821_supported_drvice_ids { +/* + * MCP48xx DAC output: + * + * Vout = (Vref * D / 2^N) * G + * + * where: + * - Vref = 2.048V (internal reference) + * - N = DAC resolution (12 bits for MCP4821) + * - G = gain selection: + * 1x when GA bit = 1 + * 2x when GA bit = 0 (default) + * + * Therefore full-scale voltage is: + * - 1x gain: 2.048V + * - 2x gain: 4.096V + * + * Scale = Vfull-scale / 2^N + */ + +enum mcp4821_supported_device_ids { ID_MCP4801, ID_MCP4802, ID_MCP4811, @@ -43,6 +62,7 @@ enum mcp4821_supported_drvice_ids { struct mcp4821_state { struct spi_device *spi; u16 dac_value[2]; + bool gain_1x; }; struct mcp4821_chip_info { @@ -57,6 +77,7 @@ struct mcp4821_chip_info { .channel = (channel_id), \ .info_mask_separate = BIT(IIO_CHAN_INFO_RAW), \ .info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE), \ + .info_mask_shared_by_type_available = BIT(IIO_CHAN_INFO_SCALE), \ .scan_type = { \ .realbits = (resolution), \ .shift = 12 - (resolution), \ @@ -122,8 +143,13 @@ static int mcp4821_read_raw(struct iio_dev *indio_dev, state = iio_priv(indio_dev); *val = state->dac_value[chan->channel]; return IIO_VAL_INT; + case IIO_CHAN_INFO_SCALE: - *val = MCP4821_2X_GAIN_VREF_MV; + state = iio_priv(indio_dev); + if (state->gain_1x) + *val = MCP4821_VREF_MV; + else + *val = MCP4821_VREF_MV * 2; *val2 = chan->scan_type.realbits; return IIO_VAL_FRACTIONAL_LOG2; default: @@ -140,34 +166,66 @@ static int mcp4821_write_raw(struct iio_dev *indio_dev, __be16 write_buffer; int ret; - if (val2 != 0) - return -EINVAL; + switch (mask) { + case IIO_CHAN_INFO_RAW: - if (val < 0 || val >= BIT(chan->scan_type.realbits)) - return -EINVAL; + if (val2 != 0) + return -EINVAL; - if (mask != IIO_CHAN_INFO_RAW) - return -EINVAL; + if (val < 0 || val >= BIT(chan->scan_type.realbits)) + return -EINVAL; + + write_val = MCP4821_ACTIVE_MODE | val << chan->scan_type.shift; + if (chan->channel) + write_val |= MCP4802_SECOND_CHAN; + if (state->gain_1x) + write_val |= MCP4821_GAIN_ENABLE; - write_val = MCP4821_ACTIVE_MODE | val << chan->scan_type.shift; - if (chan->channel) - write_val |= MCP4802_SECOND_CHAN; + write_buffer = cpu_to_be16(write_val); + ret = spi_write(state->spi, &write_buffer, sizeof(write_buffer)); + if (ret) { + dev_err(&state->spi->dev, "Failed to write to device: %d", ret); + return ret; + } - write_buffer = cpu_to_be16(write_val); - ret = spi_write(state->spi, &write_buffer, sizeof(write_buffer)); - if (ret) { - dev_err(&state->spi->dev, "Failed to write to device: %d", ret); - return ret; + state->dac_value[chan->channel] = val; + return 0; + + case IIO_CHAN_INFO_SCALE: + if (val == 1) + state->gain_1x = true; + else if (val == 2) + state->gain_1x = false; + else + return -EINVAL; + return 0; + default: + return -EINVAL; } +} - state->dac_value[chan->channel] = val; +static const int mcp4821_gain_avail[] = {1, 2}; - return 0; +static int mcp4821_read_avail(struct iio_dev *indio_dev, + struct iio_chan_spec const *chan, + const int **vals, int *type, int *length, + long info) +{ + switch (info) { + case IIO_CHAN_INFO_SCALE: + *vals = mcp4821_gain_avail; + *type = IIO_VAL_INT; + *length = 2; + return IIO_AVAIL_LIST; + default: + return -EINVAL; + } } static const struct iio_info mcp4821_info = { .read_raw = &mcp4821_read_raw, .write_raw = &mcp4821_write_raw, + .read_avail = &mcp4821_read_avail, }; static int mcp4821_probe(struct spi_device *spi) @@ -183,6 +241,9 @@ static int mcp4821_probe(struct spi_device *spi) state = iio_priv(indio_dev); state->spi = spi; + /* default gain is 2x as GA bit is active low*/ + state->gain_1x = false; + info = spi_get_device_match_data(spi); indio_dev->name = info->name; indio_dev->info = &mcp4821_info; -- 2.43.0