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

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Message-ID: <4826097d-b575-4895-9335-f587bbf3bc89@baylibre.com>
Date: Wed, 4 Sep 2024 14:01:46 +0200
From: Angelo Dureghello <adureghello@...libre.com>
To: Jonathan Cameron <jic23@...nel.org>
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

Hi Jonathan,

On 03/09/24 9:11 PM, Jonathan Cameron wrote:
> On Mon, 2 Sep 2024 16:03:22 +0200
> Angelo Dureghello <adureghello@...libre.com> wrote:
>
>> Hi Jonathan,
>>
>> thanks for the feedbacks,
>>
>> On 31/08/24 1:23 PM, Jonathan Cameron wrote:
>>> 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?
>> for this DAC IP, it is the dma buffer where i write the samples,
>> for other non-dac frontends may be something different, so i kept it
>> generic. Not sure what a proper name may be, maybe
>>
>> "Enable optional data buffer" ?
> How do you 'enable' a buffer?  Enable writing into it maybe?

for the current case, this is done using the custom register
of the AXI IP, enabling a "stream".

return regmap_set_bits(st->regmap, AXI_DAC_REG_CUSTOM_CTRL,
                    AXI_DAC_STREAM_ENABLE);

Functionally, looks like dma data is processed (sent over qspi)
when the stream is enabled.

Maybe a name as "stream_enable" would me more appropriate ?
"Stream" seems less generic btw.

>>
>>>> + * @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_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.
>>>   
>> Mainly, an IP may include a bus as 16bit parallel, or LVDS, or similar
>> to QSPI as in my case (ad3552r).
> ok.
>
> If this is a bus used for both control and dataplane, then we should really
> be presenting it as a bus (+ offload) similar to do for spi + offload.
>
>> In particular, the bus is physically as a QSPI bus, but the data format
>> over it is a bit different.
>>
>> So ad3552r needs this 5 lanes bus + double data rate to reach 33MUPS.
>>
>> https://analogdevicesinc.github.io/hdl/library/axi_ad3552r/index.html
>>
> Jonathan
>
-- 
  ,,,      Angelo Dureghello
:: :.     BayLibre -runtime team- Developer
:`___:
  `____: