Re: [PATCH v2] iio: core: register chardev only if needed

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On 4/15/20 3:56 PM, Ardelean, Alexandru wrote:
On Tue, 2020-04-14 at 19:06 +0100, Jonathan Cameron wrote:
[External]

On Tue, 14 Apr 2020 11:36:56 +0300
Alexandru Ardelean <alexandru.ardelean@xxxxxxxxxx> wrote:

The final intent is to localize all buffer ops into the
industrialio-buffer.c file, to be able to add support for multiple buffers
per IIO device.

We only need a chardev if we need to support buffers and/or events.

With this change, a chardev will be created:
1. if there is an IIO buffer attached OR
2. if there is an event_interface configured

Otherwise, no chardev will be created.
Quite a lot of IIO devices don't really need a chardev, so this is a minor
improvement to the IIO core, as the IIO device will take up fewer
resources.

Signed-off-by: Alexandru Ardelean <alexandru.ardelean@xxxxxxxxxx>
---

Changelog v1 -> v2:
* split away from series 'iio: core,buffer: re-organize chardev creation';
   i'm getting the feeling that this has some value on it's own;
   no idea if it needs 'Fixes' tag; it is a bit fuzzy to point to a patch
   which this would be fixed by this; i'm guessing it would be fine
   without one
I'd argue it's an 'optimization' rather than a fix :)

Still looks good to me but I'd like it to sit for a little while to
see if anyone points out something we are both missing!

This is not good.
It seems that I did not properly test all cases.
I had to break a device to not have an event_interface to notice that the sysfs
doesn't get instantiated either because device_add is missing.

Will do another try.

I think you also have to make the `indio_dev->dev.devt = ...` conditional. Or conditionally use device_add() instead of device_add_cdev().

If you go for the former you need to call cdev_device_del() unconditionally, for the latter call device_del() or cdev_device_del() depending on whether the cdev was registered.

- Lars





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