Re: [PATCH v3 06/11] IIO: ADC: add stm32 DFSDM support for PDM microphone

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Please find my comments in-line

Thanks and Regards,
Arnaud

On 03/19/2017 11:38 PM, Jonathan Cameron wrote:
> On 17/03/17 14:08, Arnaud Pouliquen wrote:
>> Add DFSDM driver to handle PDM audio microphones.
>>
>> Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@xxxxxx>
> So key element here is that we really need to have a proper way of
> doing DMA buffer consumers from IIO (as you said in your cover letter).
> 
> Not entirely obvious how to do this.  Would like some input from Lars
> if possible.  I'm afraid I don't have an suitable hardware to try anything
> out on (or the time really!).  This will obviously be quite different from
> the single scan stuff you have seen is there at the moment.
I saw 2 other drivers ti_am335x_adc.c and stm32_adc.c) that use cyclic
DMA. I suppose that problematics are similar. Perhaps the extra
constrains in DFSDM is the in-kernel API used to get the data.

> 
> Whether this whole approach makes sense vs doing the dma in the alsa driver
> isn't clear to me.
> 
> On the plus side, presumably we'll get love dma ADC support for free
> as part of doing it this way ;)
> 
> It's been a while since I looked at the IIO dma buffer stuff at all. Will
> try and refresh my memory sometime this week.

Ok, i will wait your feedback (and Lars's one) before updating my code
for next version.
> 
> Jonathan
>> ---
>>  drivers/iio/adc/Kconfig                   |  13 +
>>  drivers/iio/adc/Makefile                  |   1 +
>>  drivers/iio/adc/stm32-dfsdm-audio.c       | 720 ++++++++++++++++++++++++++++++
>>  include/linux/iio/adc/stm32-dfsdm-audio.h |  41 ++
>>  4 files changed, 775 insertions(+)
>>  create mode 100644 drivers/iio/adc/stm32-dfsdm-audio.c
>>  create mode 100644 include/linux/iio/adc/stm32-dfsdm-audio.h
>>
>> diff --git a/drivers/iio/adc/Kconfig b/drivers/iio/adc/Kconfig
>> index 3e0eb11..c108933 100644
>> --- a/drivers/iio/adc/Kconfig
>> +++ b/drivers/iio/adc/Kconfig
>> @@ -478,6 +478,19 @@ config STM32_DFSDM_ADC
>>  	  This driver can also be built as a module.  If so, the module
>>  	  will be called stm32-dfsdm-adc.
>>  
>> +config STM32_DFSDM_AUDIO
>> +	tristate "STMicroelectronics STM32 dfsdm audio
>> +	depends on (ARCH_STM32 && OF) || COMPILE_TEST
>> +	select STM32_DFSDM_CORE
>> +	select REGMAP_MMIO
>> +	select IIO_BUFFER_DMAENGINE
>> +	help
>> +	  Select this option to support Audio PDM micophone for
>> +	  STMicroelectronics  STM32 digital filter for sigma delta converter.
>> +
>> +	  This driver can also be built as a module.  If so, the module
>> +	  will be called stm32-dfsdm-audio.
>> +
>>  config STX104
>>  	tristate "Apex Embedded Systems STX104 driver"
>>  	depends on X86 && ISA_BUS_API
>> diff --git a/drivers/iio/adc/Makefile b/drivers/iio/adc/Makefile
>> index 161f271..79f975d 100644
>> --- a/drivers/iio/adc/Makefile
>> +++ b/drivers/iio/adc/Makefile
>> @@ -44,6 +44,7 @@ obj-$(CONFIG_STX104) += stx104.o
>>  obj-$(CONFIG_STM32_ADC_CORE) += stm32-adc-core.o
>>  obj-$(CONFIG_STM32_ADC) += stm32-adc.o
>>  obj-$(CONFIG_STM32_DFSDM_ADC) += stm32-dfsdm-adc.o
>> +obj-$(CONFIG_STM32_DFSDM_AUDIO) += stm32-dfsdm-audio.o
>>  obj-$(CONFIG_STM32_DFSDM_CORE) += stm32-dfsdm-core.o
>>  obj-$(CONFIG_TI_ADC081C) += ti-adc081c.o
>>  obj-$(CONFIG_TI_ADC0832) += ti-adc0832.o
>> diff --git a/drivers/iio/adc/stm32-dfsdm-audio.c b/drivers/iio/adc/stm32-dfsdm-audio.c
>> new file mode 100644
>> index 0000000..115ef8f
>> --- /dev/null
>> +++ b/drivers/iio/adc/stm32-dfsdm-audio.c
>> @@ -0,0 +1,720 @@
>> +/*
>> + * This file is the ADC part of of the STM32 DFSDM driver
>> + *
>> + * Copyright (C) 2017, STMicroelectronics - All Rights Reserved
>> + * Author: Arnaud Pouliquen <arnaud.pouliquen@xxxxxx>.
>> + *
>> + * License type: GPLv2
>> + *
>> + * This program is free software; you can redistribute it and/or modify it
>> + * under the terms of the GNU General Public License version 2 as published by
>> + * the Free Software Foundation.
>> + *
>> + * This program is distributed in the hope that it will be useful, but
>> + * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
>> + * or FITNESS FOR A PARTICULAR PURPOSE.
>> + * See the GNU General Public License for more details.
>> + *
>> + * You should have received a copy of the GNU General Public License along with
>> + * this program. If not, see <http://www.gnu.org/licenses/>.
>> + */
>> +
>> +#include <linux/dmaengine.h>
>> +#include <linux/dma-mapping.h>
>> +#include <linux/interrupt.h>
>> +#include <linux/module.h>
>> +#include <linux/of.h>
>> +#include <linux/platform_device.h>
>> +#include <linux/regmap.h>
>> +#include <linux/slab.h>
>> +
>> +#include <linux/iio/buffer.h>
>> +#include <linux/iio/hw_consumer.h>
>> +#include <linux/iio/sysfs.h>
>> +#include <linux/iio/trigger.h>
>> +#include <linux/iio/trigger_consumer.h>
>> +#include <linux/iio/triggered_buffer.h>
>> +
>> +#include "stm32-dfsdm.h"
>> +
>> +#define DFSDM_DMA_BUFFER_SIZE (4 * PAGE_SIZE)
>> +
>> +struct stm32_dfsdm_audio {
>> +	struct stm32_dfsdm *dfsdm;
>> +	unsigned int fl_id;
>> +	unsigned int ch_id;
>> +	unsigned int spi_freq;  /* SPI bus clock frequency */
>> +	unsigned int sample_freq; /* Sample frequency after filter decimation */
>> +
>> +	u8 *rx_buf;
>> +	unsigned int bufi; /* Buffer current position */
>> +	unsigned int buf_sz; /* Buffer size */
>> +
>> +	struct dma_chan	*dma_chan;
>> +	dma_addr_t dma_buf;
>> +
>> +	int (*cb)(const void *data, size_t size, void *cb_priv);
>> +	void *cb_priv;
>> +};
>> +
>> +const char *stm32_dfsdm_spi_trigger = DFSDM_SPI_TRIGGER_NAME;
>> +
>> +static ssize_t dfsdm_audio_get_rate(struct iio_dev *indio_dev, uintptr_t priv,
>> +				    const struct iio_chan_spec *chan, char *buf)
>> +{
>> +	struct stm32_dfsdm_audio *pdmc = iio_priv(indio_dev);
>> +
>> +	return snprintf(buf, PAGE_SIZE, "%d\n", pdmc->sample_freq);
>> +}
>> +
>> +static ssize_t dfsdm_audio_set_rate(struct iio_dev *indio_dev, uintptr_t priv,
>> +				    const struct iio_chan_spec *chan,
>> +				    const char *buf, size_t len)
>> +{
>> +	struct stm32_dfsdm_audio *pdmc = iio_priv(indio_dev);
>> +	struct stm32_dfsdm_filter *fl = &pdmc->dfsdm->fl_list[pdmc->fl_id];
>> +	struct stm32_dfsdm_channel *ch = &pdmc->dfsdm->ch_list[pdmc->ch_id];
>> +	unsigned int spi_freq = pdmc->spi_freq;
>> +	unsigned int sample_freq;
>> +	int ret;
>> +
>> +	ret = kstrtoint(buf, 0, &sample_freq);
>> +	if (ret)
>> +		return ret;
>> +
>> +	dev_dbg(&indio_dev->dev, "Requested sample_freq :%d\n", sample_freq);
>> +	if (!sample_freq)
>> +		return -EINVAL;
>> +
>> +	if (ch->src != DFSDM_CHANNEL_SPI_CLOCK_EXTERNAL)
>> +		spi_freq = pdmc->dfsdm->spi_master_freq;
>> +
>> +	if (spi_freq % sample_freq)
>> +		dev_warn(&indio_dev->dev, "Sampling rate not accurate (%d)\n",
>> +			 spi_freq / (spi_freq / sample_freq));
>> +
>> +	ret = stm32_dfsdm_set_osrs(fl, 0, (spi_freq / sample_freq));
>> +	if (ret < 0) {
>> +		dev_err(&indio_dev->dev,
>> +			"Not able to find filter parameter that match!\n");
>> +		return ret;
>> +	}
>> +	pdmc->sample_freq = sample_freq;
>> +
>> +	return len;
>> +}
>> +
>> +static ssize_t dfsdm_audio_get_spiclk(struct iio_dev *indio_dev, uintptr_t priv,
>> +				      const struct iio_chan_spec *chan,
>> +				      char *buf)
>> +{
>> +	struct stm32_dfsdm_audio *pdmc = iio_priv(indio_dev);
>> +
>> +	return snprintf(buf, PAGE_SIZE, "%d\n", pdmc->spi_freq);
>> +}
>> +
>> +static ssize_t dfsdm_audio_set_spiclk(struct iio_dev *indio_dev, uintptr_t priv,
>> +				      const struct iio_chan_spec *chan,
>> +				      const char *buf, size_t len)
>> +{
>> +	struct stm32_dfsdm_audio *pdmc = iio_priv(indio_dev);
>> +	struct stm32_dfsdm_filter *fl = &pdmc->dfsdm->fl_list[pdmc->fl_id];
>> +	struct stm32_dfsdm_channel *ch = &pdmc->dfsdm->ch_list[pdmc->ch_id];
>> +	unsigned int sample_freq = pdmc->sample_freq;
>> +	unsigned int spi_freq;
>> +	int ret;
>> +
>> +	/* If DFSDM is master on SPI, SPI freq can not be updated */
>> +	if (ch->src != DFSDM_CHANNEL_SPI_CLOCK_EXTERNAL)
>> +		return -EPERM;
>> +
>> +	ret = kstrtoint(buf, 0, &spi_freq);
>> +	if (ret)
>> +		return ret;
>> +
>> +	dev_dbg(&indio_dev->dev, "Requested frequency :%d\n", spi_freq);
>> +	if (!spi_freq)
>> +		return -EINVAL;
>> +
>> +	if (sample_freq) {
>> +		if (spi_freq % sample_freq)
>> +			dev_warn(&indio_dev->dev,
>> +				 "Sampling rate not accurate (%d)\n",
>> +				 spi_freq / (spi_freq / sample_freq));
>> +
>> +		ret = stm32_dfsdm_set_osrs(fl, 0, (spi_freq / sample_freq));
>> +		if (ret < 0) {
>> +			dev_err(&indio_dev->dev,
>> +				"No filter parameters that match!\n");
>> +			return ret;
>> +		}
>> +	}
>> +	pdmc->spi_freq = spi_freq;
>> +
>> +	return len;
>> +}
>> +
>> +/*
>> + * Define external info for SPI Frequency and audio sampling rate that can be
>> + * configured by ASoC driver through consumer.h API
>> + */
>> +static const struct iio_chan_spec_ext_info dfsdm_adc_ext_info[] = {
>> +	/* filter oversampling: Post filter oversampling ratio */
>> +	{
>> +		.name = "audio_sampling_rate",
>> +		.shared = IIO_SHARED_BY_TYPE,
>> +		.read = dfsdm_audio_get_rate,
>> +		.write = dfsdm_audio_set_rate,
>> +	},
>> +	/* data_right_bit_shift : Filter output data shifting */
>> +	{
>> +		.name = "spi_clk_freq",
>> +		.shared = IIO_SHARED_BY_TYPE,
>> +		.read = dfsdm_audio_get_spiclk,
>> +		.write = dfsdm_audio_set_spiclk,
>> +	},
>> +	{},
>> +};
>> +
>> +static int stm32_dfsdm_start_conv(struct stm32_dfsdm_audio *pdmc, bool single)
>> +{
>> +	struct regmap *regmap = pdmc->dfsdm->regmap;
>> +	int ret;
>> +
>> +	ret = stm32_dfsdm_start_dfsdm(pdmc->dfsdm);
>> +	if (ret < 0)
>> +		return ret;
>> +
>> +	ret = stm32_dfsdm_start_channel(pdmc->dfsdm, pdmc->ch_id);
>> +	if (ret < 0)
>> +		goto stop_dfsdm;
>> +
>> +	ret = stm32_dfsdm_filter_configure(pdmc->dfsdm, pdmc->fl_id,
>> +					   pdmc->ch_id);
>> +	if (ret < 0)
>> +		goto stop_channels;
>> +
>> +	/* Enable DMA transfer*/
>> +	ret = regmap_update_bits(regmap, DFSDM_CR1(pdmc->fl_id),
>> +				 DFSDM_CR1_RDMAEN_MASK, DFSDM_CR1_RDMAEN(1));
>> +	if (ret < 0)
>> +		return ret;
>> +
>> +	/* Enable conversion triggered by SPI clock*/
>> +	ret = regmap_update_bits(regmap, DFSDM_CR1(pdmc->fl_id),
>> +				 DFSDM_CR1_RCONT_MASK,  DFSDM_CR1_RCONT(1));
>> +	if (ret < 0)
>> +		return ret;
>> +
>> +	ret = stm32_dfsdm_start_filter(pdmc->dfsdm, pdmc->fl_id);
>> +	if (ret < 0)
>> +		goto stop_channels;
>> +
>> +	return 0;
>> +
>> +stop_channels:
>> +	stm32_dfsdm_stop_channel(pdmc->dfsdm, pdmc->fl_id);
>> +stop_dfsdm:
>> +	stm32_dfsdm_stop_dfsdm(pdmc->dfsdm);
>> +
>> +	return ret;
>> +}
>> +
>> +static void stm32_dfsdm_stop_conv(struct stm32_dfsdm_audio *pdmc)
>> +{
>> +	stm32_dfsdm_stop_filter(pdmc->dfsdm, pdmc->fl_id);
>> +
>> +	stm32_dfsdm_stop_channel(pdmc->dfsdm, pdmc->ch_id);
>> +
>> +	stm32_dfsdm_stop_dfsdm(pdmc->dfsdm);
>> +}
>> +
>> +static int stm32_dfsdm_set_watermark(struct iio_dev *indio_dev,
>> +				     unsigned int val)
>> +{
>> +	struct stm32_dfsdm_audio *pdmc = iio_priv(indio_dev);
>> +	unsigned int watermark = DFSDM_DMA_BUFFER_SIZE / 2;
>> +
>> +	/*
>> +	 * DMA cyclic transfers are used, buffer is split into two periods.
>> +	 * There should be :
>> +	 * - always one buffer (period) DMA is working on
>> +	 * - one buffer (period) driver pushed to ASoC side ().
>> +	 */
>> +	watermark = min(watermark, val * (unsigned int)(sizeof(u32)));
>> +	pdmc->buf_sz = watermark * 2;
>> +
>> +	return 0;
>> +}
>> +
>> +int stm32_dfsdm_validate_trigger(struct iio_dev *indio_dev,
>> +				 struct iio_trigger *trig)
>> +{
>> +	if (!strcmp(stm32_dfsdm_spi_trigger, trig->name))
>> +		return 0;
>> +
>> +	return -EINVAL;
>> +}
>> +
>> +static const struct iio_info stm32_dfsdm_info_pdmc = {
>> +	.hwfifo_set_watermark = stm32_dfsdm_set_watermark,
>> +	.driver_module = THIS_MODULE,
>> +	.validate_trigger = stm32_dfsdm_validate_trigger,
>> +};
>> +
>> +static irqreturn_t stm32_dfsdm_irq(int irq, void *arg)
>> +{
>> +	struct stm32_dfsdm_audio *pdmc = arg;
>> +	struct iio_dev *indio_dev = iio_priv_to_dev(pdmc);
>> +	struct regmap *regmap = pdmc->dfsdm->regmap;
>> +	unsigned int status;
>> +
>> +	regmap_read(regmap, DFSDM_ISR(pdmc->fl_id), &status);
>> +
>> +	if (status & DFSDM_ISR_ROVRF_MASK) {
>> +		dev_err(&indio_dev->dev, "Unexpected Conversion overflow\n");
>> +		regmap_update_bits(regmap, DFSDM_ICR(pdmc->fl_id),
>> +				   DFSDM_ICR_CLRROVRF_MASK,
>> +				   DFSDM_ICR_CLRROVRF_MASK);
>> +	}
>> +
>> +	return IRQ_HANDLED;
>> +}
>> +
>> +static unsigned int stm32_dfsdm_audio_avail_data(struct stm32_dfsdm_audio *pdmc)
>> +{
>> +	struct dma_tx_state state;
>> +	enum dma_status status;
>> +
>> +	status = dmaengine_tx_status(pdmc->dma_chan,
>> +				     pdmc->dma_chan->cookie,
>> +				     &state);
>> +	if (status == DMA_IN_PROGRESS) {
>> +		/* Residue is size in bytes from end of buffer */
>> +		unsigned int i = pdmc->buf_sz - state.residue;
>> +		unsigned int size;
>> +
>> +		/* Return available bytes */
>> +		if (i >= pdmc->bufi)
>> +			size = i - pdmc->bufi;
>> +		else
>> +			size = pdmc->buf_sz + i - pdmc->bufi;
>> +
>> +		return size;
>> +	}
>> +
>> +	return 0;
>> +}
>> +
>> +static void stm32_dfsdm_audio_dma_buffer_done(void *data)
>> +{
>> +	struct iio_dev *indio_dev = data;
>> +
>> +	iio_trigger_poll_chained(indio_dev->trig);
> This shouldn't be going through the trigger infrastructure at all really.
> I'm not 100% sure what doing so is gaining you...
Yes i will clean trigger part and call directly the ASoC callback here.
>> +}
>> +
>> +static int stm32_dfsdm_audio_dma_start(struct iio_dev *indio_dev)
>> +{
>> +	struct stm32_dfsdm_audio *pdmc = iio_priv(indio_dev);
>> +	struct dma_async_tx_descriptor *desc;
>> +	dma_cookie_t cookie;
>> +	int ret;
>> +
>> +	if (!pdmc->dma_chan)
>> +		return -EINVAL;
>> +
>> +	dev_dbg(&indio_dev->dev, "%s size=%d watermark=%d\n", __func__,
>> +		pdmc->buf_sz, pdmc->buf_sz / 2);
>> +
>> +	/* Prepare a DMA cyclic transaction */
>> +	desc = dmaengine_prep_dma_cyclic(pdmc->dma_chan,
>> +					 pdmc->dma_buf,
>> +					 pdmc->buf_sz, pdmc->buf_sz / 2,
>> +					 DMA_DEV_TO_MEM,
>> +					 DMA_PREP_INTERRUPT);
>> +	if (!desc)
>> +		return -EBUSY;
>> +
>> +	desc->callback = stm32_dfsdm_audio_dma_buffer_done;
>> +	desc->callback_param = indio_dev;
>> +
>> +	cookie = dmaengine_submit(desc);
>> +	ret = dma_submit_error(cookie);
>> +	if (ret) {
>> +		dmaengine_terminate_all(pdmc->dma_chan);
>> +		return ret;
>> +	}
>> +
>> +	/* Issue pending DMA requests */
>> +	dma_async_issue_pending(pdmc->dma_chan);
>> +
>> +	return 0;
>> +}
>> +
>> +static int stm32_dfsdm_postenable(struct iio_dev *indio_dev)
>> +{
>> +	struct stm32_dfsdm_audio *pdmc = iio_priv(indio_dev);
>> +	int ret;
>> +
>> +	dev_dbg(&indio_dev->dev, "%s\n", __func__);
>> +	/* Reset pdmc buffer index */
>> +	pdmc->bufi = 0;
>> +
>> +	ret = stm32_dfsdm_start_conv(pdmc, false);
>> +	if (ret) {
>> +		dev_err(&indio_dev->dev, "Can't start conversion\n");
>> +		return ret;
>> +	}
>> +
>> +	ret = stm32_dfsdm_audio_dma_start(indio_dev);
>> +	if (ret) {
>> +		dev_err(&indio_dev->dev, "Can't start DMA\n");
>> +		goto err_stop_conv;
>> +	}
>> +
>> +	ret = iio_triggered_buffer_postenable(indio_dev);
>> +	if (ret < 0) {
>> +		dev_err(&indio_dev->dev, "%s :%d\n", __func__, __LINE__);
>> +		goto err_stop_dma;
>> +	}
>> +
>> +	return 0;
>> +
>> +err_stop_dma:
>> +	if (pdmc->dma_chan)
>> +		dmaengine_terminate_all(pdmc->dma_chan);
>> +err_stop_conv:
>> +	stm32_dfsdm_stop_conv(pdmc);
>> +
>> +	return ret;
>> +}
>> +
>> +static int stm32_dfsdm_predisable(struct iio_dev *indio_dev)
>> +{
>> +	struct stm32_dfsdm_audio *pdmc = iio_priv(indio_dev);
>> +	int ret;
>> +
>> +	dev_dbg(&indio_dev->dev, "%s\n", __func__);
>> +	ret = iio_triggered_buffer_predisable(indio_dev);
>> +	if (ret < 0)
>> +		dev_err(&indio_dev->dev, "Predisable failed\n");
>> +
>> +	if (pdmc->dma_chan)
>> +		dmaengine_terminate_all(pdmc->dma_chan);
>> +
>> +	stm32_dfsdm_stop_conv(pdmc);
>> +
>> +	return 0;
>> +}
>> +
>> +static const struct iio_buffer_setup_ops stm32_dfsdm_buffer_setup_ops = {
>> +	.postenable = &stm32_dfsdm_postenable,
>> +	.predisable = &stm32_dfsdm_predisable,
>> +};
>> +
>> +static irqreturn_t stm32_dfsdm_audio_trigger_handler(int irq, void *p)
>> +{
> OK. So now I kind of understand what the trigger provided in the adc driver
> was about.  hmm.  Triggers are supposed to be per sample so this is indeed
> a hack.  We need fullblown DMA buffer consumers to do this right.
Yes exactly.
> 
> Probably best person to comment on that is Lars. 
>> +	struct iio_poll_func *pf = p;
>> +	struct iio_dev *indio_dev = pf->indio_dev;
>> +	struct stm32_dfsdm_audio *pdmc = iio_priv(indio_dev);
>> +	size_t old_pos;
>> +	int available = stm32_dfsdm_audio_avail_data(pdmc);
>> +
>> +	/*
>> +	 * Buffer interface is not support cyclic DMA buffer,and offer only
>> +	 * an interface to push data samples per samples.
>> +	 * For this reason iio_push_to_buffers_with_timestamp in not used
>> +	 * and interface is hacked using a private callback registered by ASoC.
>> +	 * This should be a temporary solution waiting a cyclic DMA engine
>> +	 * support in IIO.
>> +	 */
>> +
>> +	dev_dbg(&indio_dev->dev, "%s: pos = %d, available = %d\n", __func__,
>> +		pdmc->bufi, available);
>> +	old_pos = pdmc->bufi;
>> +	while (available >= indio_dev->scan_bytes) {
>> +		u32 *buffer = (u32 *)&pdmc->rx_buf[pdmc->bufi];
>> +
>> +		/* Mask 8 LSB that contains the channel ID */
>> +		*buffer &= 0xFFFFFF00;
>> +		available -= indio_dev->scan_bytes;
>> +		pdmc->bufi += indio_dev->scan_bytes;
>> +		if (pdmc->bufi >= pdmc->buf_sz) {
>> +			if (pdmc->cb)
>> +				pdmc->cb(&pdmc->rx_buf[old_pos],
>> +					 pdmc->buf_sz - old_pos, pdmc->cb_priv);
>> +			pdmc->bufi = 0;
>> +			old_pos = 0;
>> +		}
>> +	}
>> +	if (pdmc->cb)
>> +		pdmc->cb(&pdmc->rx_buf[old_pos], pdmc->bufi - old_pos,
>> +				pdmc->cb_priv);
>> +
>> +	iio_trigger_notify_done(indio_dev->trig);
>> +
>> +	return IRQ_HANDLED;
>> +}
>> +
>> +/**
>> + * stm32_dfsdm_get_buff_cb - register a callback
>> + *	that will be called when DMA transfer period is achieved.
>> + *
>> + * @iio_dev: Handle to IIO device.
>> + * @cb: pointer to callback function.
>> + *	@data: pointer to data buffer
>> + *	@size: size in byte of the data buffer
>> + *	@private: pointer to consumer private structure
>> + * @private: pointer to consumer private structure
>> + */
>> +int stm32_dfsdm_get_buff_cb(struct iio_dev *iio_dev,
>> +			    int (*cb)(const void *data, size_t size,
>> +				      void *private),
>> +			    void *private)
>> +{
>> +	struct stm32_dfsdm_audio *pdmc;
>> +
>> +	if (!iio_dev)
>> +		return -EINVAL;
>> +	pdmc = iio_priv(iio_dev);
>> +
>> +	if (iio_dev !=  iio_priv_to_dev(pdmc))
>> +		return -EINVAL;
>> +
>> +	pdmc->cb = cb;
>> +	pdmc->cb_priv = private;
>> +
>> +	return 0;
>> +}
>> +EXPORT_SYMBOL_GPL(stm32_dfsdm_get_buff_cb);
>> +
>> +/**
>> + * stm32_dfsdm_release_buff_cb - unregister buffer callback
>> + *
>> + * @iio_dev: Handle to IIO device.
>> + */
>> +int stm32_dfsdm_release_buff_cb(struct iio_dev *iio_dev)
>> +{
>> +	struct stm32_dfsdm_audio *pdmc;
>> +
>> +	if (!iio_dev)
>> +		return -EINVAL;
>> +	pdmc = iio_priv(iio_dev);
>> +
>> +	if (iio_dev !=  iio_priv_to_dev(pdmc))
>> +		return -EINVAL;
>> +	pdmc->cb = NULL;
>> +	pdmc->cb_priv = NULL;
>> +
>> +	return 0;
>> +}
>> +EXPORT_SYMBOL_GPL(stm32_dfsdm_release_buff_cb);
>> +
>> +static int stm32_dfsdm_audio_chan_init(struct iio_dev *indio_dev)
>> +{
>> +	struct iio_chan_spec *ch;
>> +	struct stm32_dfsdm_audio *pdmc = iio_priv(indio_dev);
>> +	int ret;
>> +
>> +	ch = devm_kzalloc(&indio_dev->dev, sizeof(*ch), GFP_KERNEL);
>> +	if (!ch)
>> +		return -ENOMEM;
>> +
>> +	ret = stm32_dfsdm_channel_parse_of(pdmc->dfsdm, indio_dev, ch, 0);
>> +	if (ret < 0)
>> +		return ret;
>> +
>> +	ch->type = IIO_VOLTAGE;
>> +	ch->indexed = 1;
>> +	ch->scan_index = 0;
>> +	ch->ext_info = dfsdm_adc_ext_info;
>> +
>> +	ch->scan_type.sign = 's';
>> +	ch->scan_type.realbits = 24;
>> +	ch->scan_type.storagebits = 32;
>> +
>> +	pdmc->ch_id = ch->channel;
>> +	ret = stm32_dfsdm_chan_configure(pdmc->dfsdm,
>> +					 &pdmc->dfsdm->ch_list[ch->channel]);
>> +
>> +	indio_dev->num_channels = 1;
>> +	indio_dev->channels = ch;
>> +
>> +	return ret;
>> +}
>> +
>> +static const struct of_device_id stm32_dfsdm_audio_match[] = {
>> +	{ .compatible = "st,stm32-dfsdm-audio"},
>> +	{}
>> +};
>> +
>> +static int stm32_dfsdm_audio_dma_request(struct iio_dev *indio_dev)
>> +{
>> +	struct stm32_dfsdm_audio *pdmc = iio_priv(indio_dev);
>> +	struct dma_slave_config config;
>> +	int ret;
>> +
>> +	pdmc->dma_chan = dma_request_slave_channel(&indio_dev->dev, "rx");
>> +	if (!pdmc->dma_chan)
>> +		return -EINVAL;
>> +
>> +	pdmc->rx_buf = dma_alloc_coherent(pdmc->dma_chan->device->dev,
>> +					 DFSDM_DMA_BUFFER_SIZE,
>> +					 &pdmc->dma_buf, GFP_KERNEL);
>> +	if (!pdmc->rx_buf) {
>> +		ret = -ENOMEM;
>> +		goto err_release;
>> +	}
>> +
>> +	/* Configure DMA channel to read data register */
>> +	memset(&config, 0, sizeof(config));
>> +	config.src_addr = (dma_addr_t)pdmc->dfsdm->phys_base;
>> +	config.src_addr += DFSDM_RDATAR(pdmc->fl_id);
>> +	config.src_addr_width = DMA_SLAVE_BUSWIDTH_4_BYTES;
>> +
>> +	ret = dmaengine_slave_config(pdmc->dma_chan, &config);
>> +	if (ret)
>> +		goto err_free;
>> +
>> +	return 0;
>> +
>> +err_free:
>> +	dma_free_coherent(pdmc->dma_chan->device->dev, DFSDM_DMA_BUFFER_SIZE,
>> +			  pdmc->rx_buf, pdmc->dma_buf);
>> +err_release:
>> +	dma_release_channel(pdmc->dma_chan);
>> +
>> +	return ret;
>> +}
>> +
>> +static int stm32_dfsdm_audio_probe(struct platform_device *pdev)
>> +{
>> +	struct device *dev = &pdev->dev;
>> +	struct stm32_dfsdm_audio *pdmc;
>> +	struct device_node *np = dev->of_node;
>> +	struct iio_dev *iio;
>> +	char *name;
>> +	int ret, irq, val;
>> +
>> +	iio = devm_iio_device_alloc(dev, sizeof(*pdmc));
>> +	if (IS_ERR(iio)) {
>> +		dev_err(dev, "%s: Failed to allocate IIO\n", __func__);
>> +		return PTR_ERR(iio);
>> +	}
>> +
>> +	pdmc = iio_priv(iio);
>> +	if (IS_ERR(pdmc)) {
>> +		dev_err(dev, "%s: Failed to allocate ADC\n", __func__);
>> +		return PTR_ERR(pdmc);
>> +	}
>> +	pdmc->dfsdm = dev_get_drvdata(dev->parent);
>> +
>> +	iio->name = np->name;
>> +	iio->dev.parent = dev;
>> +	iio->dev.of_node = np;
>> +	iio->info = &stm32_dfsdm_info_pdmc;
>> +	iio->modes = INDIO_DIRECT_MODE;
>> +
>> +	platform_set_drvdata(pdev, pdmc);
>> +
>> +	ret = of_property_read_u32(dev->of_node, "reg", &pdmc->fl_id);
>> +	if (ret != 0) {
>> +		dev_err(dev, "Missing reg property\n");
>> +		return -EINVAL;
>> +	}
>> +
>> +	name = kzalloc(sizeof("dfsdm-pdm0"), GFP_KERNEL);
>> +	if (!name)
>> +		return -ENOMEM;
>> +	snprintf(name, sizeof("dfsdm-pdm0"), "dfsdm-pdm%d", pdmc->fl_id);
>> +	iio->name = name;
>> +
>> +	/*
>> +	 * In a first step IRQs generated for channels are not treated.
>> +	 * So IRQ associated to filter instance 0 is dedicated to the Filter 0.
>> +	 */
>> +	irq = platform_get_irq(pdev, 0);
>> +	ret = devm_request_irq(dev, irq, stm32_dfsdm_irq,
>> +			       0, pdev->name, pdmc);
>> +	if (ret < 0) {
>> +		dev_err(dev, "Failed to request IRQ\n");
>> +		return ret;
>> +	}
>> +
>> +	ret = of_property_read_u32(dev->of_node, "st,filter-order", &val);
>> +	if (ret < 0) {
>> +		dev_err(dev, "Failed to set filter order\n");
>> +		return ret;
>> +	}
>> +	pdmc->dfsdm->fl_list[pdmc->fl_id].ford = val;
>> +
>> +	ret = of_property_read_u32(dev->of_node, "st,filter0-sync", &val);
>> +	if (!ret)
>> +		pdmc->dfsdm->fl_list[pdmc->fl_id].sync_mode = val;
>> +
>> +	ret = stm32_dfsdm_audio_chan_init(iio);
>> +	if (ret < 0)
>> +		return ret;
>> +
>> +	ret = stm32_dfsdm_audio_dma_request(iio);
>> +	if (ret) {
>> +		dev_err(&pdev->dev, "DMA request failed\n");
>> +		return ret;
>> +	}
>> +
>> +	iio->modes |= INDIO_BUFFER_SOFTWARE;
>> +
>> +	ret = iio_triggered_buffer_setup(iio,
>> +					 &iio_pollfunc_store_time,
>> +					 &stm32_dfsdm_audio_trigger_handler,
>> +					 &stm32_dfsdm_buffer_setup_ops);
>> +	if (ret) {
>> +		dev_err(&pdev->dev, "Buffer setup failed\n");
>> +		goto err_dma_disable;
>> +	}
>> +
>> +	ret = iio_device_register(iio);
>> +	if (ret) {
>> +		dev_err(&pdev->dev, "IIO dev register failed\n");
>> +		goto err_buffer_cleanup;
>> +	}
>> +
>> +	return 0;
>> +
>> +err_buffer_cleanup:
>> +	iio_triggered_buffer_cleanup(iio);
>> +
>> +err_dma_disable:
>> +	if (pdmc->dma_chan) {
>> +		dma_free_coherent(pdmc->dma_chan->device->dev,
>> +				  DFSDM_DMA_BUFFER_SIZE,
>> +				  pdmc->rx_buf, pdmc->dma_buf);
>> +		dma_release_channel(pdmc->dma_chan);
>> +	}
>> +
>> +	return ret;
>> +}
>> +
>> +static int stm32_dfsdm_audio_remove(struct platform_device *pdev)
>> +{
>> +	struct stm32_dfsdm_audio *pdmc = platform_get_drvdata(pdev);
>> +	struct iio_dev *iio = iio_priv_to_dev(pdmc);
>> +
>> +	iio_device_unregister(iio);
> Same as in the other driver. Can just use the devm_iio_device_register
> version and drop remove.
oops missing the previous comment... sorry.
>> +
>> +	return 0;
>> +}
>> +
>> +static struct platform_driver stm32_dfsdm_audio_driver = {
>> +	.driver = {
>> +		.name = "stm32-dfsdm-audio",
>> +		.of_match_table = stm32_dfsdm_audio_match,
>> +	},
>> +	.probe = stm32_dfsdm_audio_probe,
>> +	.remove = stm32_dfsdm_audio_remove,
>> +};
>> +module_platform_driver(stm32_dfsdm_audio_driver);
>> +
>> +MODULE_DESCRIPTION("STM32 sigma delta converter for PDM microphone");
>> +MODULE_AUTHOR("Arnaud Pouliquen <arnaud.pouliquen@xxxxxx>");
>> +MODULE_LICENSE("GPL v2");
>> diff --git a/include/linux/iio/adc/stm32-dfsdm-audio.h b/include/linux/iio/adc/stm32-dfsdm-audio.h
>> new file mode 100644
>> index 0000000..9b41b28
>> --- /dev/null
>> +++ b/include/linux/iio/adc/stm32-dfsdm-audio.h
>> @@ -0,0 +1,41 @@
>> +/*
>> + * This file discribe the STM32 DFSDM IIO driver API for audio part
>> + *
>> + * Copyright (C) 2017, STMicroelectronics - All Rights Reserved
>> + * Author(s): Arnaud Pouliquen <arnaud.pouliquen@xxxxxx>.
>> + *
>> + * License terms: GPL V2.0.
>> + *
>> + * This program is free software; you can redistribute it and/or modify it
>> + * under the terms of the GNU General Public License version 2 as published by
>> + * the Free Software Foundation.
>> + *
>> + * This program is distributed in the hope that it will be useful, but
>> + * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
>> + * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
>> + * details.
>> + */
>> +#ifndef STM32_DFSDM_AUDIO_H
>> +#define STM32_DFSDM_AUDIO_H
>> +
>> +/**
>> + * stm32_dfsdm_get_buff_cb() - register callback for capture buffer period.
>> + * @dev:	Pointer to client device.
>> + * @indio_dev:	Device on which the channel exists.
>> + * @cb:		Callback function.
>> + *		@data:  pointer to data buffer
>> + *		@size: size of the data buffer in bytes
>> + * @private:	Private data passed to callback.
>> + *
>> + */
>> +int stm32_dfsdm_get_buff_cb(struct iio_dev *iio_dev,
>> +			    int (*cb)(const void *data, size_t size,
>> +				      void *private),
>> +			    void *private);
>> +/**
>> + * stm32_dfsdm_get_buff_cb() - release callback for capture buffer period.
>> + * @indio_dev:	Device on which the channel exists.
>> + */
>> +int stm32_dfsdm_release_buff_cb(struct iio_dev *iio_dev);
>> +
>> +#endif
>>
> 
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