Re: [PATCH 1/6] gpio: make the gpiochip a real device

[Linus Walleij <linus.walleij@xxxxxxxxxx>]

On Mon, Nov 16, 2015 at 3:27 PM, Linus Walleij <linus.walleij@xxxxxxxxxx> wrote:

> If I don't use device_add()/device_del(), I see this must mean I have to use
> device_register()/device_unregister() as the latter only decrease the refcount
> and wait for the instance to die off.
>
> So am I reading it correctly if I understand that this is what we should be
> doing? I.e device_register()/device_unregister() and then wait for the
> .remove() call to do its deed, so the kobj/struct device is kept around if
> e.g. sysfs or the chardev has open files.

Hard to get advice on design here I see. Anyways, the clean thing to
do (after some weeks of thinking) seems to be this:

1. Introduce a void *data into gpio_chip and gpiochip_set_data()
   gpiochip_get_data() set/get it.

2. Replace all occurences of container_of() dereferencing in all
   GPIO drivers with gpiochip_[set|get]_data() so as to avoid having
   gpio_chip to be embedded into state containers.

3-1. Split gpio_chip in a static descriptor with a vtable for callbacks
   and other static config called struct gpio_chip, and
   struct gpio_device that is returned as a pointer from
   gpiochip_add(). It will need to be free:ed by gpiodevice_remove()
   after that.

3-2. In the same patch set rename all functions to indicate that
   we are now operating on a gpio_device not a gpio_chip.

3-3. After a GPIO driver issues gpio_device_unregister()
   it may stay around if there are still references to the
   struct device.

This is a very tiresome refactoring, but I'm growing confident that
it is what needs to happen to manage gpio devices in the future.

After step 3-3 we have a clean gpio_device containing a
struct device, and from there we apply the initial chardev
interface.

Yours,
Linus Walleij
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