Re: [PATCH 4/4] iio: dac: stm32: add support for waveform generator

[Jonathan Cameron <jic23@kernel.org>]

On 31/03/17 12:45, Fabrice Gasnier wrote:
> STM32 DAC has built-in noise or triangle waveform generator.
> Waveform generator requires trigger to be configured.
> - "wave" extended attribute selects noise or triangle.
> - "mamp" extended attribute selects either LFSR (linear feedback
>   shift register) mask for noise waveform, OR triangle amplitude.
> 
> Signed-off-by: Fabrice Gasnier <fabrice.gasnier@st.com>

Looks like AN3126 is the relevant doc.
(a quick note from this relevant to earlier patches- doc says
1-3 channels - perhaps build that from the start with that
possibility in mind).

As you probably know, this wanders into a large chunk of 'poorly'
defined ABI within IIO as it stands.

Note there are a number of waveform generators still in staging.
Not a lot of movement on getting them out of staging unfortunately
(so far!)

However, let us keep those drivers in mind as we work on ABI and
I definitely want some input from someone at Analog. 
Lars, who is best for this? I see at least some of these were
originally Michael's work.

They do have partial docs under
drivers/staging/iio/Documentation/sysfs-bus-iio-dds
I'll highlight thoughts from there as I look through this...


> ---
>  Documentation/ABI/testing/sysfs-bus-iio-dac-stm32 |  32 ++++++
>  drivers/iio/dac/stm32-dac.c                       | 124 ++++++++++++++++++++++
>  2 files changed, 156 insertions(+)
>  create mode 100644 Documentation/ABI/testing/sysfs-bus-iio-dac-stm32
> 
> diff --git a/Documentation/ABI/testing/sysfs-bus-iio-dac-stm32 b/Documentation/ABI/testing/sysfs-bus-iio-dac-stm32
> new file mode 100644
> index 0000000..c2432e1
> --- /dev/null
> +++ b/Documentation/ABI/testing/sysfs-bus-iio-dac-stm32
> @@ -0,0 +1,32 @@
> +What:		/sys/bus/iio/devices/iio:deviceX/wave
> +What:		/sys/bus/iio/devices/iio:deviceX/wave_available
Needs to be channel associated. Whilst in your case you have basically
a pair of single channel devices, in more general case, it's not usual
to have multiple parallel waveform generators clocked together.

Old ABI is:
What:		/sys/bus/iio/devices/.../out_altvoltageX_outY_wavetype etc


> +KernelVersion:	4.12
> +Contact:	fabrice.gasnier@st.com
> +Description:
> +		List and/or select waveform generation provided by STM32 DAC:
> +		- "none": (default) means normal DAC operations
none kind of hints at nothing coming out.  Perhaps 'flat' would be closer?
i.e. only changes when someone tells it to.

> +		- "noise": select noise waveform
> +		- "triangle": select triangle waveform
> +		Note: when waveform generator is used, writing _raw sysfs entry
> +		adds a DC offset to generated waveform. Reading it reports
> +		current output value.
Interesting.  This gets fiddly but one option would be to describe the whole
device as a dds.

Then we have flat type above, combined with an _offset.

> +
> +What:		/sys/bus/iio/devices/iio:deviceX/mamp
> +What:		/sys/bus/iio/devices/iio:deviceX/mamp_available
> +KernelVersion:	4.12
> +Contact:	fabrice.gasnier@st.com
> +Description:
> +		List and select mask/amplitude used for noise/triangle waveform
> +		generator, which are:
> +		- "0": unmask bit 0 of LFSR / triangle amplitude equal to 1
> +		- "1": unmask bit [1:0] of LFSR / triangle amplitude equal to 3
> +		- "2": unmask bit [2:0] of LFSR / triangle amplitude equal to 7
> +		- "3": unmask bit [3:0] of LFSR / triangle amplitude equal to 15
> +		- "4": unmask bit [4:0] of LFSR / triangle amplitude equal to 31
> +		- "5": unmask bit [5:0] of LFSR / triangle amplitude equal to 63
> +		- "6": unmask bit [6:0] of LFSR / triangle amplitude equal to 127
> +		- "7": unmask bit [7:0] of LFSR / triangle amplitude equal to 255
> +		- "8": unmask bit [8:0] of LFSR / triangle amplitude equal to 511
> +		- "9": unmask bit [9:0] of LFSR / triangle amplitude equal to 1023
> +		- "10": unmask bit [10:0] of LFSR / triangle amplitude equal to 2047
> +		- "11": unmask bit [11:0] of LFSR / triangle amplitude equal to 4095
I don't fully understand what is going on here - so I'm guessing somewhat.


Let us try describing these generically.  If we define standard 'forms' of each
waveform type.  Say a 0 to 1 V peak to peak, then we could use _scale to control
this nicely.

> diff --git a/drivers/iio/dac/stm32-dac.c b/drivers/iio/dac/stm32-dac.c
> index 62e43e9..d7dda78 100644
> --- a/drivers/iio/dac/stm32-dac.c
> +++ b/drivers/iio/dac/stm32-dac.c
> @@ -41,10 +41,14 @@
>  /**
>   * struct stm32_dac - private data of DAC driver
>   * @common:		reference to DAC common data
> + * @wave:		waveform generator
> + * @mamp:		waveform mask/amplitude
>   * @swtrig:		Using software trigger
>   */
>  struct stm32_dac {
>  	struct stm32_dac_common *common;
> +	u32 wave;
> +	u32 mamp;
>  	bool swtrig;
>  };
>  
> @@ -157,6 +161,24 @@ static int stm32_dac_is_enabled(struct stm32_dac *dac, int channel)
>  	return !!en;
>  }
>  
> +static int stm32_dac_wavegen(struct stm32_dac *dac, int channel)
> +{
> +	struct regmap *regmap = dac->common->regmap;
> +	u32 mask, val;
> +
> +	if (channel == STM32_DAC_CHANNEL_1) {
> +		val = FIELD_PREP(STM32_DAC_CR_WAVE1, dac->wave) |
> +			FIELD_PREP(STM32_DAC_CR_MAMP1, dac->mamp);
> +		mask = STM32_DAC_CR_WAVE1 | STM32_DAC_CR_MAMP1;
> +	} else {
> +		val = FIELD_PREP(STM32_DAC_CR_WAVE2, dac->wave) |
> +			FIELD_PREP(STM32_DAC_CR_MAMP2, dac->mamp);
> +		mask = STM32_DAC_CR_WAVE2 | STM32_DAC_CR_MAMP2;
> +	}
> +
> +	return regmap_update_bits(regmap, STM32_DAC_CR, mask, val);
> +}
> +
>  static int stm32_dac_enable(struct iio_dev *indio_dev, int channel)
>  {
>  	struct stm32_dac *dac = iio_priv(indio_dev);
> @@ -164,6 +186,17 @@ static int stm32_dac_enable(struct iio_dev *indio_dev, int channel)
>  		STM32_DAC_CR_EN1 : STM32_DAC_CR_EN2;
>  	int ret;
>  
> +	if (dac->wave && !indio_dev->trig) {
> +		dev_err(&indio_dev->dev, "Wavegen requires a trigger\n");
> +		return -EINVAL;
> +	}
> +
> +	ret = stm32_dac_wavegen(dac, channel);
> +	if (ret < 0) {
> +		dev_err(&indio_dev->dev, "Wavegen setup failed\n");
> +		return ret;
> +	}
> +
>  	ret = stm32_dac_set_trig(dac, indio_dev->trig, channel);
>  	if (ret < 0) {
>  		dev_err(&indio_dev->dev, "Trigger setup failed\n");
> @@ -291,6 +324,96 @@ static int stm32_dac_debugfs_reg_access(struct iio_dev *indio_dev,
>  	.driver_module = THIS_MODULE,
>  };
>  
> +/* waveform generator wave selection */
> +static const char * const stm32_dac_wave_desc[] = {
> +	"none",
> +	"noise",
> +	"triangle",
> +};
> +
> +static int stm32_dac_set_wave(struct iio_dev *indio_dev,
> +			      const struct iio_chan_spec *chan,
> +			      unsigned int type)
> +{
> +	struct stm32_dac *dac = iio_priv(indio_dev);
> +
> +	if (stm32_dac_is_enabled(dac, chan->channel))
> +		return -EBUSY;
> +	dac->wave = type;
> +
> +	return 0;
> +}
> +
> +static int stm32_dac_get_wave(struct iio_dev *indio_dev,
> +			      const struct iio_chan_spec *chan)
> +{
> +	struct stm32_dac *dac = iio_priv(indio_dev);
> +
> +	return dac->wave;
> +}
> +
> +static const struct iio_enum stm32_dac_wave_enum = {
> +	.items = stm32_dac_wave_desc,
> +	.num_items = ARRAY_SIZE(stm32_dac_wave_desc),
> +	.get = stm32_dac_get_wave,
> +	.set = stm32_dac_set_wave,
> +};
> +
> +/*
> + * waveform generator mask/amplitude selection:
> + * - noise: LFSR mask (linear feedback shift register, umasks bit 0, [1:0]...)
> + * - triangle: amplitude (equal to 1, 3, 5, 7... 4095)
> + */
> +static const char * const stm32_dac_mamp_desc[] = {
> +	"0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "10", "11",
> +};
> +
> +static int stm32_dac_set_mamp(struct iio_dev *indio_dev,
> +			      const struct iio_chan_spec *chan,
> +			      unsigned int type)
> +{
> +	struct stm32_dac *dac = iio_priv(indio_dev);
> +
> +	if (stm32_dac_is_enabled(dac, chan->channel))
> +		return -EBUSY;
> +	dac->mamp = type;
> +
> +	return 0;
> +}
> +
> +static int  stm32_dac_get_mamp(struct iio_dev *indio_dev,
> +			       const struct iio_chan_spec *chan)
> +{
> +	struct stm32_dac *dac = iio_priv(indio_dev);
> +
> +	return dac->mamp;
> +}
> +
> +static const struct iio_enum stm32_dac_mamp_enum = {
> +	.items = stm32_dac_mamp_desc,
> +	.num_items = ARRAY_SIZE(stm32_dac_mamp_desc),
> +	.get = stm32_dac_get_mamp,
> +	.set = stm32_dac_set_mamp,
> +};
> +
> +static const struct iio_chan_spec_ext_info stm32_dac_ext_info[] = {
> +	IIO_ENUM("wave", IIO_SHARED_BY_ALL, &stm32_dac_wave_enum),
> +	{
> +		.name = "wave_available",
> +		.shared = IIO_SHARED_BY_ALL,
> +		.read = iio_enum_available_read,
> +		.private = (uintptr_t)&stm32_dac_wave_enum,
> +	},
> +	IIO_ENUM("mamp", IIO_SHARED_BY_ALL, &stm32_dac_mamp_enum),
> +	{
> +		.name = "mamp_available",
> +		.shared = IIO_SHARED_BY_ALL,
> +		.read = iio_enum_available_read,
> +		.private = (uintptr_t)&stm32_dac_mamp_enum,
> +	},
> +	{},
> +};
> +
>  #define STM32_DAC_CHANNEL(chan, name) {		\
>  	.type = IIO_VOLTAGE,			\
>  	.indexed = 1,				\
> @@ -306,6 +429,7 @@ static int stm32_dac_debugfs_reg_access(struct iio_dev *indio_dev,
>  		.storagebits = 16,		\
>  	},					\
>  	.datasheet_name = name,			\
> +	.ext_info = stm32_dac_ext_info		\
>  }
>  
>  static const struct iio_chan_spec stm32_dac_channels[] = {
>