Re: [PATCH] iio: adc: ad799x: use devm_iio_device_register and devm buffer setup

[David Lechner]

On 2/28/26 11:19 AM, Archit Anant wrote:
> Hi David,
> 
> On Sat, Feb 28, 2026 at 10:06 PM David Lechner <dlechner@xxxxxxxxxxxx> wrote:
>>
>> On 2/28/26 9:45 AM, Archit Anant wrote:
>>> Convert the driver to use the device-managed versions of
>>> iio_device_register() and iio_triggered_buffer_setup().
>>>
>>> This simplifies the error handling in ad799x_probe() by removing the
>>> 'error_cleanup_ring' goto label. It also removes the need to manually
>>> call iio_device_unregister() and iio_triggered_buffer_cleanup() in
>>> ad799x_remove().
>>>
>> Since we are doing this, why not also handle the regulators and
>> rx_buf so that we can drop the remove() function completely?
> 
> I completely agree that dropping the remove() function is the
> ideal end state but I initially stopped short of doing that because of two
> hurdles:
> 
> 1. regulators: since ad799x_read_raw() needs the regulator pointers
> to call regulator_get_voltage(), I couldn't simply use
> devm_regulator_get_enable().

In this case, we can use devm_add_action_or_reset() to register the
disable callbacks.

> 
> 2. rx_buf: st->rx_buf is dynamically re-allocated (kfree then kmalloc)
> inside ad799x_update_scan_mode() based on the scan mask. If I use
> devm_kmalloc there, it would leak memory on every mask change.
> 
> To drop remove() completely, would you prefer I use devm_add_action_or_reset()
> to register custom disable & free callbacks for the regulators and the
> final state of rx_buf?
> 
> If that approach sounds good to you, I will gladly prepare a v2 that
> eliminates the remove() function entirely.
> 
> 

Here, we could also use devm_add_action_or_reset() or we could drop
the dynamic allocation altogether and make rx_buf large enough for
the largest transfer. The latter would be preferred as that is how
we usually do it in general.

#define AD799X_MAX_CHANNELS 8

...

struct ad799x_state {
	...
	unsigned int			transfer_size;
	IIO_DECLARE_DMA_BUFFER_WITH_TS(__be16, rx_buf, AD799X_MAX_CHANNELS);
};

Note, it is important for this to be the last field in the struct
for DMA alignment purposes.