Re: [PATCH v2 03/10] iio: adc: mcp3911: add support for buffers

[Marcus Folkesson <marcus.folkesson@gmail.com>]

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Hi Jonathan,

On Sat, Jun 25, 2022 at 12:45:37PM +0100, Jonathan Cameron wrote:
> On Sat, 25 Jun 2022 12:38:46 +0200
> Marcus Folkesson <marcus.folkesson@gmail.com> wrote:
> 
> > Add support for buffers to make the driver fit for more usecases.
> > 
> > Signed-off-by: Marcus Folkesson <marcus.folkesson@gmail.com>
> Hi Marcus,
> 
> Good to see this feature.  A few comments inline, mostly around
> optimising the data flow / device accesses.
> 
> Thanks,
> 
> Jonathan
> 
> > ---
> > 
> > Notes:
> >     v2:
> >         - No changes
> > 
> >  drivers/iio/adc/mcp3911.c | 58 ++++++++++++++++++++++++++++++++++++++-
> >  1 file changed, 57 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/iio/adc/mcp3911.c b/drivers/iio/adc/mcp3911.c
> > index 25a235cce56c..2a4bf374f140 100644
> > --- a/drivers/iio/adc/mcp3911.c
> > +++ b/drivers/iio/adc/mcp3911.c
> > @@ -9,6 +9,10 @@
> >  #include <linux/delay.h>
> >  #include <linux/err.h>
> >  #include <linux/iio/iio.h>
> > +#include <linux/iio/buffer.h>
> > +#include <linux/iio/triggered_buffer.h>
> > +#include <linux/iio/trigger_consumer.h>
> > +#include <linux/iio/trigger.h>
> >  #include <linux/module.h>
> >  #include <linux/mod_devicetable.h>
> >  #include <linux/property.h>
> > @@ -54,6 +58,10 @@ struct mcp3911 {
> >  	struct regulator *vref;
> >  	struct clk *clki;
> >  	u32 dev_addr;
> > +	struct {
> > +		u32 channels[2];
> > +		s64 ts __aligned(8);
> > +	} scan;
> >  };
> >  
> >  static int mcp3911_read(struct mcp3911 *adc, u8 reg, u32 *val, u8 len)
> > @@ -187,16 +195,58 @@ static int mcp3911_write_raw(struct iio_dev *indio_dev,
> >  		.type = IIO_VOLTAGE,				\
> >  		.indexed = 1,					\
> >  		.channel = idx,					\
> > +		.scan_index = idx,				\
> >  		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |	\
> >  			BIT(IIO_CHAN_INFO_OFFSET) |		\
> >  			BIT(IIO_CHAN_INFO_SCALE),		\
> > +		.scan_type = {					\
> > +			.sign = 's',				\
> > +			.realbits = 24,				\
> > +			.storagebits = 32,			\
> > +		},						\
> >  }
> >  
> >  static const struct iio_chan_spec mcp3911_channels[] = {
> >  	MCP3911_CHAN(0),
> >  	MCP3911_CHAN(1),
> > +	IIO_CHAN_SOFT_TIMESTAMP(2),
> >  };
> >  
> > +static irqreturn_t mcp3911_trigger_handler(int irq, void *p)
> > +{
> > +	struct iio_poll_func *pf = p;
> > +	struct iio_dev *indio_dev = pf->indio_dev;
> > +	struct mcp3911 *adc = iio_priv(indio_dev);
> > +	int scan_index;
> > +	int i = 0;
> > +	u32 val;
> > +
> > +	mutex_lock(&adc->lock);
> > +	for_each_set_bit(scan_index, indio_dev->active_scan_mask,
> > +			indio_dev->masklength) {
> > +		const struct iio_chan_spec *scan_chan =
> > +			&indio_dev->channels[scan_index];
> > +		int ret = mcp3911_read(adc,
> > +				MCP3911_CHANNEL(scan_chan->channel), &val, 3);
> 
> I was a bit surprised not to see some overlap of address setting and
> read out here if both channels are enabled, so opened up the data sheet.
> 
> Can we take advantage of "Continuous communication looping on address set"

Sure, I will make it use continuous reads when both channels are enabled,
thanks.

> (6.7 on the datasheet).  Also for buffered capture we'd normally make
> things like shifting and endian conversion a userspace problem.  Can we
> not do that here for some reason?  You'd need to take care to ensure

The endian conversion&shifting was actually the reason for why I did not
make use of continoues reads from the beginning.

> any buffers that might be used directly for DMA obey DMA safety rules
> (currently avoided by using spi_write_then_read), but it would be
> nice to do less data manipulation int his path if we can.

I will change to spi_sync() and skip the data manipulation.

> 
> 
> 
> > +
> > +		if (ret < 0) {
> > +			dev_warn(&adc->spi->dev,
> > +					"failed to get conversion data\n");
> > +			goto out;
> > +		}
> > +
> > +		adc->scan.channels[i] = val;
> > +		i++;
> > +	}
> > +	iio_push_to_buffers_with_timestamp(indio_dev, &adc->scan,
> > +			iio_get_time_ns(indio_dev));  
> > +out:
> > +	mutex_unlock(&adc->lock);
> > +	iio_trigger_notify_done(indio_dev->trig);
> > +
> > +	return IRQ_HANDLED;
> > +}
> > +
> >  static const struct iio_info mcp3911_info = {
> >  	.read_raw = mcp3911_read_raw,
> >  	.write_raw = mcp3911_write_raw,
> > @@ -303,7 +353,7 @@ static int mcp3911_probe(struct spi_device *spi)
> >  		goto clk_disable;
> >  
> >  	indio_dev->name = spi_get_device_id(spi)->name;
> > -	indio_dev->modes = INDIO_DIRECT_MODE;
> > +	indio_dev->modes = INDIO_DIRECT_MODE | INDIO_BUFFER_TRIGGERED;
> 
> The core sets INDIO_BUFFER_TRIGGERED as part of devm_iio_triggered_buffer_setup()
> so you need to set DIRECT_MODE here (that one isn't visible to the core)

Ok, thank you. I sent patches that fixes this in two other ADC-drivers
as well to avoid more people following the same thing.

> 
> >  	indio_dev->info = &mcp3911_info;
> >  	spi_set_drvdata(spi, indio_dev);
> >  
> > @@ -312,6 +362,12 @@ static int mcp3911_probe(struct spi_device *spi)
> >  
> >  	mutex_init(&adc->lock);
> >  
> > +	ret = devm_iio_triggered_buffer_setup(&spi->dev, indio_dev,
> Can't use devm here for the same reason it was inappropriate in patch 2.
> 
> I'd suggest a precursor patch(es) to move the driver fully over to
> devm_ managed such that you don't need a remove function and the ordering
> is maintained.

Yep, I will keep this and fix patch 2 instead.

> > +			NULL,
> > +			mcp3911_trigger_handler, NULL);
> > +	if (ret)
> > +		goto clk_disable;
> > +
> >  	ret = devm_iio_device_register(&adc->spi->dev, indio_dev);
> >  	if (ret)
> >  		goto clk_disable;
> 

/Marcus

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