linux-kernel - Re: [PATCH RFC 2/8] iio: backend: extend features

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Message-ID: <20240831122313.4d993260@jic23-huawei>
Date: Sat, 31 Aug 2024 12:23:13 +0100
From: Jonathan Cameron <jic23@...nel.org>
To: Angelo Dureghello <adureghello@...libre.com>
Cc: Lars-Peter Clausen <lars@...afoo.de>, Michael Hennerich
 <Michael.Hennerich@...log.com>, Nuno Sá <nuno.sa@...log.com>,
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>, Olivier Moysan
 <olivier.moysan@...s.st.com>, linux-iio@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 dlechner@...libre.com
Subject: Re: [PATCH RFC 2/8] iio: backend: extend features

On Thu, 29 Aug 2024 14:32:00 +0200
Angelo Dureghello <adureghello@...libre.com> wrote:

> From: Angelo Dureghello <adureghello@...libre.com>
> 
> Extend backend features with new calls needed later on this
> patchset from axi version of ad3552r.
> 
> A bus type property has been added to the devicetree to
> inform the backend about the type of bus (interface) in use
> bu the IP.
> 
> The follwoing calls are added:
> 
> iio_backend_ext_sync_enable
> 	enable synchronize channels on external trigger
> iio_backend_ext_sync_disable
> 	disable synchronize channels on external trigger
> iio_backend_ddr_enable
> 	enable ddr bus transfer
> iio_backend_ddr_disable
> 	disable ddr bus transfer
> iio_backend_set_bus_mode
> 	select the type of bus, so that specific read / write
> 	operations are performed accordingly
> 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.
> iio_backend_bus_reg_read
> 	generic bus read, bus-type dependent
> iio_backend_bus_read_write
> 	generic bus write, bus-type dependent
> 
> Signed-off-by: Angelo Dureghello <adureghello@...libre.com>
> ---
>  drivers/iio/industrialio-backend.c | 151 +++++++++++++++++++++++++++++++++++++
>  include/linux/iio/backend.h        |  24 ++++++
>  2 files changed, 175 insertions(+)
> 
> diff --git a/drivers/iio/industrialio-backend.c b/drivers/iio/industrialio-backend.c
> index a52a6b61c8b5..1f60c8626be7 100644
> --- a/drivers/iio/industrialio-backend.c
> +++ b/drivers/iio/industrialio-backend.c
> @@ -718,6 +718,157 @@ static int __devm_iio_backend_get(struct device *dev, struct iio_backend *back)
>  	return 0;
>  }


> +
> +/**
> + * iio_backend_buffer_enable - Enable data buffering

Data buffering is a very vague term.  Perhaps some more detail on what
this means?

> + * @back: Backend device
> + *
> + * RETURNS:
> + * 0 on success, negative error number on failure.
> + */
> +int iio_backend_buffer_enable(struct iio_backend *back)
> +{
> +	return iio_backend_op_call(back, buffer_enable);
> +}
> +EXPORT_SYMBOL_NS_GPL(iio_backend_buffer_enable, IIO_BACKEND);
> +
> +/**
> + * iio_backend_set_buffer_disable - Disable data buffering
> + * @back: Backend device
> + *
> + * RETURNS:
> + * 0 on success, negative error number on failure.
> + */
> +int iio_backend_buffer_disable(struct iio_backend *back)
> +{
> +	return iio_backend_op_call(back, buffer_disable);
> +}
> +EXPORT_SYMBOL_NS_GPL(iio_backend_buffer_disable, IIO_BACKEND);
> +
> +/**
> + * iio_backend_buffer_transfer_addr - Set data address.
> + * @back: Backend device
> + * @chan_address: Channel register address
Run scripts/kernel-doc on this and fix the errors (parameter name is 
wrong).  W=1 builds might also point the simpler ones out.
> + *
> + * Some devices may need to inform the backend about an address/location
> + * where to read or write the data.
I'd drop the 'location' part unless this gets used later because you
are referring register address above.
> + *
> + * RETURNS:
> + * 0 on success, negative error number on failure.
> + */
> +int iio_backend_data_transfer_addr(struct iio_backend *back, u32 address)
> +{
> +	return iio_backend_op_call(back, data_transfer_addr, address);
> +}
> +EXPORT_SYMBOL_NS_GPL(iio_backend_data_transfer_addr, IIO_BACKEND);
> +
> +/**
> + * iio_backend_bus_reg_read - Read from the interface bus
> + * @back: Backend device
> + * @reg: Register valule
> + * @val: Pointer to register value
> + * @size: Size, in bytes
> + *
> + * A backend may operate on a specific interface with a related bus.
> + * Read from the interface bus.

So this is effectively routing control plane data through the offloaded
bus?  That sounds a lot more like a conventional bus than IIO backend.
Perhaps it should be presented as that with the IIO device attached
to that bus? I don't fully understand what is wired up here.

> + *
> + * RETURNS:
> + * 0 on success, negative error number on failure.
> + */
> +int iio_backend_bus_reg_read(struct iio_backend *back,
> +			     u32 reg, void *val, size_t size)
> +{
> +	if (!size)
> +		return -EINVAL;
> +
> +	return iio_backend_op_call(back, bus_reg_read, reg, val, size);
> +}
> +EXPORT_SYMBOL_NS_GPL(iio_backend_bus_reg_read, IIO_BACKEND);
> +