linux-kernel - Re: [PATCH v5 2/6] iio: backend: add support for data size set

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Message-ID: <2c831de5-3dc5-4a60-a92e-beef95b023e1@baylibre.com>
Date: Fri, 1 Nov 2024 14:23:13 -0500
From: David Lechner <dlechner@...libre.com>
To: Antoniu Miclaus <antoniu.miclaus@...log.com>, jic23@...nel.org,
 conor+dt@...nel.org, linux-iio@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-pwm@...r.kernel.org
Subject: Re: [PATCH v5 2/6] iio: backend: add support for data size set

On 11/1/24 6:23 AM, Antoniu Miclaus wrote:
> Add backend support for setting the data size used.
> This setting can be adjusted within the IP cores interfacing devices.
> 
> Signed-off-by: Antoniu Miclaus <antoniu.miclaus@...log.com>
> ---
> no changes in v5.
>  drivers/iio/industrialio-backend.c | 21 +++++++++++++++++++++
>  include/linux/iio/backend.h        |  3 +++
>  2 files changed, 24 insertions(+)
> 
> diff --git a/drivers/iio/industrialio-backend.c b/drivers/iio/industrialio-backend.c
> index c792cd1e24e8..6f4e38417dfd 100644
> --- a/drivers/iio/industrialio-backend.c
> +++ b/drivers/iio/industrialio-backend.c
> @@ -660,6 +660,27 @@ int iio_backend_interface_type_get(struct iio_backend *back,
>  }
>  EXPORT_SYMBOL_NS_GPL(iio_backend_interface_type_get, IIO_BACKEND);
>  
> +/**
> + * iio_backend_data_size_set - set the data width/size in the data bus.
> + * @back: Backend device
> + * @size: Size in bits
> + *
> + * Some frontend devices can dynamically control the word/data size on the
> + * interface/data bus. Hence, the backend device needs to be aware of it so
> + * data can be correctly transferred.
> + *
> + * Return:
> + * 0 on success, negative error number on failure.
> + */
> +size_t iio_backend_data_size_set(struct iio_backend *back, size_t size)

Should be returning int, not size_t.

Also, size_t for size parameter seems a bit much when this is taking bits.
I don't think anything is ever going to need 5 billion bits. :-p

> +{
> +	if (!size)
> +		return -EINVAL;
> +
> +	return iio_backend_op_call(back, data_size_set, size);
> +}
> +EXPORT_SYMBOL_NS_GPL(iio_backend_data_size_set, IIO_BACKEND);
> +
>  /**
>   * iio_backend_extend_chan_spec - Extend an IIO channel
>   * @back: Backend device
> diff --git a/include/linux/iio/backend.h b/include/linux/iio/backend.h
> index e5ea90f1c3e0..83ca4f0124db 100644
> --- a/include/linux/iio/backend.h
> +++ b/include/linux/iio/backend.h
> @@ -93,6 +93,7 @@ enum iio_backend_interface_type {
>   * @ext_info_set: Extended info setter.
>   * @ext_info_get: Extended info getter.
>   * @interface_type_get: Interface type.
> + * @data_size_set: Data size.
>   * @read_raw: Read a channel attribute from a backend device
>   * @debugfs_print_chan_status: Print channel status into a buffer.
>   * @debugfs_reg_access: Read or write register value of backend.
> @@ -130,6 +131,7 @@ struct iio_backend_ops {
>  			    const struct iio_chan_spec *chan, char *buf);
>  	int (*interface_type_get)(struct iio_backend *back,
>  				  enum iio_backend_interface_type *type);
> +	int (*data_size_set)(struct iio_backend *back, ssize_t size);
>  	int (*read_raw)(struct iio_backend *back,
>  			struct iio_chan_spec const *chan, int *val, int *val2,
>  			long mask);
> @@ -180,6 +182,7 @@ ssize_t iio_backend_ext_info_get(struct iio_dev *indio_dev, uintptr_t private,
>  				 const struct iio_chan_spec *chan, char *buf);
>  int iio_backend_interface_type_get(struct iio_backend *back,
>  				   enum iio_backend_interface_type *type);
> +size_t iio_backend_data_size_set(struct iio_backend *back, size_t size);

This will need to be changed as well.

>  int iio_backend_read_raw(struct iio_backend *back,
>  			 struct iio_chan_spec const *chan, int *val, int *val2,
>  			 long mask);