linux-kernel - Re: [PATCH 4/4] iio: dac: ad3552r-hs: add support for internal ramp

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Message-ID: <68db2225-4519-4436-bee2-24fbe320ac4f@baylibre.com>
Date: Fri, 28 Mar 2025 11:40:10 -0500
From: David Lechner <dlechner@...libre.com>
To: Nuno Sá <noname.nuno@...il.com>,
 Angelo Dureghello <adureghello@...libre.com>, Nuno Sá
 <nuno.sa@...log.com>, Jonathan Cameron <jic23@...nel.org>,
 Lars-Peter Clausen <lars@...afoo.de>, Jonathan Corbet <corbet@....net>,
 Olivier Moysan <olivier.moysan@...s.st.com>,
 Michael Hennerich <Michael.Hennerich@...log.com>
Cc: linux-iio@...r.kernel.org, linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/4] iio: dac: ad3552r-hs: add support for internal ramp

On 3/28/25 3:28 AM, Nuno Sá wrote:
> On Fri, 2025-03-21 at 21:28 +0100, Angelo Dureghello wrote:
>> From: Angelo Dureghello <adureghello@...libre.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@...libre.com>
>> ---

...

>> +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;
>> +
>> +	ret = simple_write_to_buffer(buf, sizeof(buf) - 1, ppos, userbuf,
>> +				     count);
>> +	if (ret < 0)
>> +		return ret;
>> +
>> +	buf[count] = 0;
>> +
>> +	if (count == 10 && !strncmp(buf, "iio-buffer", 10)) {
>> +		ret = ad3552r_hs_set_data_source(st, IIO_BACKEND_EXTERNAL);
>> +		if (ret)
>> +			return ret;
>> +	} else if (count == 22 && !strncmp(buf, "backend-ramp-generator", 22)) {
>> +		ret = ad3552r_hs_set_data_source(st,
>> +			IIO_BACKEND_INTERNAL_RAMP_16BIT);
>> +		if (ret)
>> +			return ret;
>> +	} else {
>> +		return -EINVAL;
>> +	}
> 
> Are we expected to add more data types in the future? If not, this could be simply an
> enable/disable ramp generator thing... It would be much simpler.

Angelo actually had implemented it that way originally. :-)

I suggested to change it to a string because the HDL project for this family
of DACs actually has 3 possibilities for the data source:

	* Selectable input source: DMA/ADC/TEST_RAMP;

And there are other potential sources from the generic AXI DAC like
0x00: internal tone (DDS) that seems somewhat likely to be seen in the future.

> 
> Anyways, you could define a static array and use match_string()?
> 
> Lastly, for insterfaces like this, it's always helpful to have an _available kind of
> attribute.
> 
> - Nuno Sá
> 
> 
> 
>>  
>>  static const struct of_device_id ad3552r_hs_of_id[] = {
>>
> 
>