Re: [PATCH v3 5/5] iio: dac: ad3552r-hs: add support for internal ramp

["Nuno Sá" <noname.nuno@gmail.com>]

On Mon, 2025-04-07 at 10:52 +0200, Angelo Dureghello wrote:
> From: Angelo Dureghello <adureghello@baylibre.com>
> 
> The ad3552r can be feeded from the HDL controller by an internally
> generated 16bit ramp, useful for debug pourposes. Add debugfs a file
> to enable or disable it.
> 
> Signed-off-by: Angelo Dureghello <adureghello@baylibre.com>
> ---
>  drivers/iio/dac/ad3552r-hs.c | 124 ++++++++++++++++++++++++++++++++++++++++--
> -
>  1 file changed, 118 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/iio/dac/ad3552r-hs.c b/drivers/iio/dac/ad3552r-hs.c
> index
> 37397e188f225a8099745ec03f7c604da76960b1..3dcbda23c732f5f5e655bde31c5dab496055
> 4bfc 100644
> --- a/drivers/iio/dac/ad3552r-hs.c
> +++ b/drivers/iio/dac/ad3552r-hs.c
> @@ -7,6 +7,7 @@
>   */
>  
>  #include <linux/bitfield.h>
> +#include <linux/debugfs.h>
>  #include <linux/delay.h>
>  #include <linux/gpio/consumer.h>
>  #include <linux/iio/backend.h>
> @@ -54,8 +55,13 @@ struct ad3552r_hs_state {
>  	struct ad3552r_hs_platform_data *data;
>  	/* INTERFACE_CONFIG_D register cache, in DDR we cannot read values.
> */
>  	u32 config_d;
> +	/* Protects backend I/O operations from concurrent accesses. */
> +	struct mutex lock;
>  };
>  
> +static const char dbgfs_src_iio_buffer[] = "iio-buffer";
> +static const char dbgfs_src_backend_ramp_gen[] = "backend-ramp-generator";
> +

Why not having both strings in one array? See below...

>  static int ad3552r_hs_reg_read(struct ad3552r_hs_state *st, u32 reg, u32
> *val,
>  			       size_t xfer_size)
>  {
> @@ -65,6 +71,18 @@ static int ad3552r_hs_reg_read(struct ad3552r_hs_state *st,
> u32 reg, u32 *val,
>  	return st->data->bus_reg_read(st->back, reg, val, xfer_size);
>  }
>  
> +static int ad3552r_hs_set_data_source(struct ad3552r_hs_state *st,
> +				      enum iio_backend_data_source type)
> +{
> +	int ret;
> +
> +	ret = iio_backend_data_source_set(st->back, 0, type);
> +	if (ret)
> +		return ret;
> +
> +	return iio_backend_data_source_set(st->back, 1, type);

Do we have some number of channels variable in some chip info? If so, I would
loop over that. If not, disregard the comment...

> +}
> +
>  static int ad3552r_hs_update_reg_bits(struct ad3552r_hs_state *st, u32 reg,
>  				      u32 mask, u32 val, size_t xfer_size)
>  {
> @@ -483,6 +501,76 @@ static int ad3552r_hs_reg_access(struct iio_dev
> *indio_dev, unsigned int reg,
>  	return st->data->bus_reg_write(st->back, reg, writeval, 1);
>  }
>  
> +static ssize_t ad3552r_hs_show_data_source(struct file *f, char __user
> *userbuf,
> +					   size_t count, loff_t *ppos)
> +{
> +	struct ad3552r_hs_state *st = file_inode(f)->i_private;
> +	enum iio_backend_data_source type;
> +	int ret;
> +
> +	guard(mutex)(&st->lock);
> +
> +	ret = iio_backend_data_source_get(st->back, 0, &type);
> +	if (ret)
> +		return ret;
> +
> +	switch (type) {
> +	case IIO_BACKEND_INTERNAL_RAMP_16BIT:
> +		return simple_read_from_buffer(userbuf, count, ppos,
> +			dbgfs_src_backend_ramp_gen,
> +			strlen(dbgfs_src_backend_ramp_gen));
> +	case IIO_BACKEND_EXTERNAL:
> +		return simple_read_from_buffer(userbuf, count, ppos,
> +			dbgfs_src_iio_buffer, strlen(dbgfs_src_iio_buffer));

Even with only one array, you could easily handle things here...

> +	default:
> +		return -EINVAL;
> +	}
> +}
> +
> +static ssize_t ad3552r_hs_write_data_source(struct file *f,
> +					    const char __user *userbuf,
> +					    size_t count, loff_t *ppos)
> +{
> +	struct ad3552r_hs_state *st = file_inode(f)->i_private;
> +	char buf[64];
> +	int ret, len;
> +
> +	guard(mutex)(&st->lock);
> +
> +	ret = simple_write_to_buffer(buf, sizeof(buf) - 1, ppos, userbuf,
> +				     count);
> +	if (ret < 0)
> +		return ret;
> +
> +	len = strlen(dbgfs_src_iio_buffer);
> +	if (count == len && !strncmp(buf, dbgfs_src_iio_buffer, len)) {
> +		ret = ad3552r_hs_set_data_source(st, IIO_BACKEND_EXTERNAL);
> +		if (ret)
> +			return ret;
> +		goto exit_ok;
> +	}
> +
> +	len = strlen(dbgfs_src_backend_ramp_gen);
> +	if (count == len && !strncmp(buf, dbgfs_src_backend_ramp_gen, len)) {
> +		ret = ad3552r_hs_set_data_source(st,
> +			IIO_BACKEND_INTERNAL_RAMP_16BIT);
> +		if (ret)
> +			return ret;
> +		goto exit_ok;
> +	}

But here is where it makes more sense... I would use match_string() and then get
the match index and translate that into the backend signal type.

Plus, I still think you could provide a 'data_source_available' attribute to
make the user interface more friendly.

- Nuno Sá
> +
> +	return -EINVAL;
> +
> +exit_ok:
> +	return count;
> +}
> +
> +static const struct file_operations ad3552r_hs_data_source_fops = {
> +	.owner = THIS_MODULE,
> +	.write = ad3552r_hs_write_data_source,
> +	.read = ad3552r_hs_show_data_source,
> +};
> +
>  static int ad3552r_hs_setup(struct ad3552r_hs_state *st)
>  {
>  	u16 id;
> @@ -550,11 +638,7 @@ static int ad3552r_hs_setup(struct ad3552r_hs_state *st)
>  	if (ret)
>  		return ret;
>  
> -	ret = iio_backend_data_source_set(st->back, 0, IIO_BACKEND_EXTERNAL);
> -	if (ret)
> -		return ret;
> -
> -	ret = iio_backend_data_source_set(st->back, 1, IIO_BACKEND_EXTERNAL);
> +	ret = ad3552r_hs_set_data_source(st, IIO_BACKEND_EXTERNAL);
>  	if (ret)
>  		return ret;
>  
> @@ -661,6 +745,24 @@ static const struct iio_info ad3552r_hs_info = {
>  	.debugfs_reg_access = &ad3552r_hs_reg_access,
>  };
>  
> +static void ad3552r_hs_debugfs_init(struct iio_dev *indio_dev)
> +{
> +	struct ad3552r_hs_state *st = iio_priv(indio_dev);
> +	struct dentry *d = iio_get_debugfs_dentry(indio_dev);
> +
> +	if (!IS_ENABLED(CONFIG_DEBUG_FS))
> +		return;
> +
> +	d = iio_get_debugfs_dentry(indio_dev);
> +	if (!d) {
> +		dev_warn(st->dev, "can't set debugfs in driver dir\n");
> +		return;
> +	}
> +
> +	debugfs_create_file("data_source", 0600, d, st,
> +			    &ad3552r_hs_data_source_fops);
> +}
> +
>  static int ad3552r_hs_probe(struct platform_device *pdev)
>  {
>  	struct ad3552r_hs_state *st;
> @@ -705,7 +807,17 @@ static int ad3552r_hs_probe(struct platform_device *pdev)
>  	if (ret)
>  		return ret;
>  
> -	return devm_iio_device_register(&pdev->dev, indio_dev);
> +	ret = devm_iio_device_register(&pdev->dev, indio_dev);
> +	if (ret)
> +		return ret;
> +
> +	ret = devm_mutex_init(&pdev->dev, &st->lock);
> +	if (ret)
> +		return ret;
> +
> +	ad3552r_hs_debugfs_init(indio_dev);
> +
> +	return ret;
>  }
>  
>  static const struct of_device_id ad3552r_hs_of_id[] = {