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Thu, 26 Mar 2026 00:13:22 -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 v2] iio: dac: mcp4821: add configurable gain support Date: Thu, 26 Mar 2026 12:42:42 +0530 Message-ID: <20260326071242.9218-1-nikhilgtr@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260321180707.73a7ad60@jic23-huawei> References: <20260321180707.73a7ad60@jic23-huawei> 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 --- drivers/iio/dac/mcp4821.c | 105 ++++++++++++++++++++++++++++++-------- 1 file changed, 83 insertions(+), 22 deletions(-) diff --git a/drivers/iio/dac/mcp4821.c b/drivers/iio/dac/mcp4821.c index 748bdca9a964..362ca12988dc 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) @@ -177,12 +235,15 @@ static int mcp4821_probe(struct spi_device *spi) const struct mcp4821_chip_info *info; indio_dev = devm_iio_device_alloc(&spi->dev, sizeof(*state)); - if (indio_dev == NULL) + if (!indio_dev) return -ENOMEM; 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