[alsa-devel] [RFC] ucb1400 touchscreen, irq auto probing and ac97 with its private field

[Jaroslav Kysela]

On Fri, 25 Apr 2008, Takashi Iwai wrote:

> Hm, indeed it's more than a single value...
> 
> For multiple anonymous data, we can use a data with a key like below:
> 
> 	struct device_hint {
> 		char *key;
> 		void *data;
> 		struct list_head list;
> 	};
> 
> and the controller driver assigns the data like
> 
> 	controller_init()
> 	{
> 		...
> 		controller.hint.key = "ucb1000-irq";
> 		controller.hint.data = whatever;
> 		list_add(&controller.hint. &ac97->device_hint_list);
> 		...
> 	}
> 
> and the device driver retrieves the data like
> 
> 	device_init()
> 	{
> 		struct device_hint *hint;
> 		hint = device_hint_get(&ac97->device_hint_list, "ucb1000-irq");
> 		if (hint) {
> 			whatever = hint->data;
> 			...
> 		}
> 	}
> 
> where device_hint_get() is defined like
> 
> 	struct device_hint *device_hint_get(struct device_hint *head,
> 			const char *key)
> 	{
> 		struct device_hint *hint;
> 		list_for_each_entry(hint, head, list)
> 			if (!strcmp(hint, key))
> 				return hint;
> 		return NULL;
> 	}
> 
> Of course, we can cast via container_of() to a container type instead
> of using a void pointer there.
> 
> This is obviously an overweight for a single use-case, but if we have
> more and more complex ones, maybe worth to consider.

Sure. I applied the simple 'void *device_private_data' patch, because 
current usage request is really trivial. We can implement complex code to 
handle data for multiple "extra" devices on AC97 bus later.

						Jaroslav

-----
Jaroslav Kysela <perex at perex.cz>
Linux Kernel Sound Maintainer
ALSA Project, Red Hat, Inc.