Re: [PATCH v3 1/7] driver core: auxiliary bus: add device creation helpers

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Tue, Feb 11, 2025 at 06:27:58PM +0100, Jerome Brunet wrote:
> Add helper functions to create a device on the auxiliary bus.
> 
> This is meant for fairly simple usage of the auxiliary bus, to avoid having
> the same code repeated in the different drivers.
> 
> Suggested-by: Stephen Boyd <sboyd@kernel.org>
> Cc: Arnd Bergmann <arnd@arndb.de>
> Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
> ---
>  drivers/base/auxiliary.c      | 88 +++++++++++++++++++++++++++++++++++++++++++
>  include/linux/auxiliary_bus.h | 10 +++++
>  2 files changed, 98 insertions(+)

I like the idea, see much the same of what I recently did for the "faux"
bus here:
	https://lore.kernel.org/all/2025021023-sandstorm-precise-9f5d@gregkh/

Some review comments:

> diff --git a/drivers/base/auxiliary.c b/drivers/base/auxiliary.c
> index afa4df4c5a3f371b91d8dd8c4325495d32ad1291..0f697c9c243dc9a50498a52362806db594345faf 100644
> --- a/drivers/base/auxiliary.c
> +++ b/drivers/base/auxiliary.c
> @@ -385,6 +385,94 @@ void auxiliary_driver_unregister(struct auxiliary_driver *auxdrv)
>  }
>  EXPORT_SYMBOL_GPL(auxiliary_driver_unregister);
>  
> +static void auxiliary_device_release(struct device *dev)
> +{
> +	struct auxiliary_device *auxdev = to_auxiliary_dev(dev);
> +
> +	kfree(auxdev);
> +}
> +
> +static struct auxiliary_device *auxiliary_device_create(struct device *dev,
> +							const char *modname,
> +							const char *devname,
> +							void *platform_data,

Can you have the caller set the platform_data if they need/want it after
the device is created?  Or do you need that in the probe callback?

And can't this be a global function too for those that don't want to
deal with devm stuff?

> +							int id)
> +{
> +	struct auxiliary_device *auxdev;
> +	int ret;
> +
> +	auxdev = kzalloc(sizeof(*auxdev), GFP_KERNEL);
> +	if (!auxdev)
> +		return ERR_PTR(-ENOMEM);

Ick, who cares what the error value really is?  Why not just do NULL or
a valid pointer?  That makes the caller much simpler to handle, right?

> +
> +	auxdev->id = id;
> +	auxdev->name = devname;
> +	auxdev->dev.parent = dev;
> +	auxdev->dev.platform_data = platform_data;
> +	auxdev->dev.release = auxiliary_device_release;
> +	device_set_of_node_from_dev(&auxdev->dev, dev);
> +
> +	ret = auxiliary_device_init(auxdev);

Only way this will fail is if you forgot to set parent or a valid name.
So why not check for devname being non-NULL above this?

> +	if (ret) {
> +		kfree(auxdev);
> +		return ERR_PTR(ret);
> +	}
> +
> +	ret = __auxiliary_device_add(auxdev, modname);
> +	if (ret) {
> +		/*
> +		 * NOTE: It may look odd but auxdev should not be freed
> +		 * here. auxiliary_device_uninit() calls device_put()
> +		 * which call the device release function, freeing auxdev.
> +		 */
> +		auxiliary_device_uninit(auxdev);

Yes it is odd, are you SURE you should be calling device_del() on the
device if this fails?  auxiliary_device_uninit(), makes sense so why not
just call that here?

> +		return ERR_PTR(ret);
> +	}
> +
> +	return auxdev;
> +}
> +
> +static void auxiliary_device_destroy(void *_auxdev)
> +{
> +	struct auxiliary_device *auxdev = _auxdev;
> +
> +	auxiliary_device_delete(auxdev);
> +	auxiliary_device_uninit(auxdev);
> +}
> +
> +/**
> + * __devm_auxiliary_device_create - create a device on the auxiliary bus
> + * @dev: parent device
> + * @modname: module name used to create the auxiliary driver name.
> + * @devname: auxiliary bus device name
> + * @platform_data: auxiliary bus device platform data
> + * @id: auxiliary bus device id
> + *
> + * Device managed helper to create an auxiliary bus device.
> + * The device create matches driver 'modname.devname' on the auxiliary bus.
> + */
> +struct auxiliary_device *__devm_auxiliary_device_create(struct device *dev,
> +							const char *modname,
> +							const char *devname,
> +							void *platform_data,
> +							int id)
> +{
> +	struct auxiliary_device *auxdev;
> +	int ret;
> +
> +	auxdev = auxiliary_device_create(dev, modname, devname, platform_data, id);
> +	if (IS_ERR(auxdev))
> +		return auxdev;
> +
> +	ret = devm_add_action_or_reset(dev, auxiliary_device_destroy,
> +				       auxdev);

Oh this is going to be messy, but I trust that callers know what they
are doing here.  Good luck!  :)

thanks,

greg k-h