Re: [PATCH v4 06/11] iio: backend: extend features

["Nuno Sá" <noname.nuno@gmail.com>]

On Thu, 2024-10-03 at 19:29 +0200, Angelo Dureghello wrote:
> From: Angelo Dureghello <adureghello@baylibre.com>
> 
> Extend backend features with new calls needed later on this
> patchset from axi version of ad3552r.
> 
> The follwoing calls are added:
> 
> iio_backend_ddr_enable
> 	enable ddr bus transfer
> iio_backend_ddr_disable
> 	disable ddr bus transfer
> iio_backend_buffer_enable
> 	enable buffer
> iio_backend_buffer_disable
> 	disable buffer
> iio_backend_data_transfer_addr
> 	define the target register address where the DAC sample
> 	will be written.
> 
> Signed-off-by: Angelo Dureghello <adureghello@baylibre.com>
> ---
>  drivers/iio/industrialio-backend.c | 79 ++++++++++++++++++++++++++++++++++++++
>  include/linux/iio/backend.h        | 17 ++++++++
>  2 files changed, 96 insertions(+)
> 
> diff --git a/drivers/iio/industrialio-backend.c b/drivers/iio/industrialio-
> backend.c
> index 20b3b5212da7..d5e0a4da761e 100644
> --- a/drivers/iio/industrialio-backend.c
> +++ b/drivers/iio/industrialio-backend.c
> @@ -718,6 +718,85 @@ static int __devm_iio_backend_get(struct device *dev, struct
> iio_backend *back)
>  	return 0;
>  }
>  
> +/**
> + * iio_backend_ddr_enable - Enable interface DDR (Double Data Rate) mode
> + * @back: Backend device
> + *
> + * Enable DDR, data is generated by the IP at each front (raising and falling)
> + * of the bus clock signal.
> + *
> + * RETURNS:
> + * 0 on success, negative error number on failure.
> + */
> +int iio_backend_ddr_enable(struct iio_backend *back)
> +{
> +	return iio_backend_op_call(back, ddr_enable);
> +}
> +EXPORT_SYMBOL_NS_GPL(iio_backend_ddr_enable, IIO_BACKEND);
> +
> +/**
> + * iio_backend_ddr_disable - Disable interface DDR (Double Data Rate) mode
> + * @back: Backend device
> + *
> + * Disable DDR, setting into SDR mode (Single Data Rate).
> + *
> + * RETURNS:
> + * 0 on success, negative error number on failure.
> + */
> +int iio_backend_ddr_disable(struct iio_backend *back)
> +{
> +	return iio_backend_op_call(back, ddr_disable);
> +}
> +EXPORT_SYMBOL_NS_GPL(iio_backend_ddr_disable, IIO_BACKEND);
> +
> +/**
> + * iio_backend_dma_stream_enable - Enable iio buffering
> + * @back: Backend device
> + *
> + * Enabling sending the dma data stream over the bus.
> + * bus interface.
> + *
> + * RETURNS:
> + * 0 on success, negative error number on failure.
> + */
> +int iio_backend_dma_stream_enable(struct iio_backend *back)
> +{
> +	return iio_backend_op_call(back, dma_stream_enable);
> +}
> +EXPORT_SYMBOL_NS_GPL(iio_backend_dma_stream_enable, IIO_BACKEND);
> +
> +/**
> + * iio_backend_dma_stream_disable - Disable iio buffering
> + * @back: Backend device
> + *
> + * Disable sending the dma data stream over the bus.
> + *
> + * RETURNS:
> + * 0 on success, negative error number on failure.
> + */
> +int iio_backend_dma_stream_disable(struct iio_backend *back)
> +{
> +	return iio_backend_op_call(back, dma_stream_disable);
> +}
> +EXPORT_SYMBOL_NS_GPL(iio_backend_dma_stream_disable, IIO_BACKEND);
> +

I'm not sure if this is what Jonathan was suggesting... Ate least I don't really
agree with it. I mean, yes, this is about buffering and to start receiving (or
sending) a stream of data. But AFAICT, it might have nothing to do with DMA. Same as
.request_buffer() - It's pretty much always a DMA one but we should not take that for
granted.

So going back to the RFC [1], you can see I was suggesting something like struct
iio_buffer_setup_ops. Maybe just add the ones we use for now? So that would
be.buffer_postenable() and .buffer_predisable(). Like this, it should be obvious the
intent of the ops.

- Nuno Sá