Re: [alsa-devel] [PATCH] ASoC: wm8962: Convert to devm_input_allocate_device()

[Dmitry Torokhov <dmitry.torokhov@gmail.com>]

On Mon, Apr 29, 2013 at 08:47:37PM +0300, Leon Romanovsky wrote:
> On Mon, Apr 29, 2013 at 1:19 PM, Mark Brown <broonie@kernel.org> wrote:
> > On Sun, Apr 28, 2013 at 09:32:18PM +0300, Leon Romanovsky wrote:
> >
> >> I think the reason of our misunderstanding is due to the name of
> >> input_free_device call. From the code, it is device destroy function,
> >> and the freeing itself done as an error handling of
> >> input_register_device
> >> (http://lxr.free-electrons.com/source/drivers/input/input.c#L2114).
> >
> >> How do you think we need to proceed? Do I need to send patches with
> >> explicit call to input_free_device function?
> >
> > I really think the input API needs to be looked at here, this is all way
> > too error prone.  Calling input_free_device() on something allocated
> > using devm_ looks like an error itself...
> In general, I agree with you, but I think we both agree that the
> current patch is not working as expected.
> The problem is that you allocated device with devm_ and later at the
> code you tried to register it, but failed. In this case no one will
> call to devres_destroy, because it is done at unregister stage only.
> 
> I see two possible solutions:
> 1. short one - fix your patches
> 2. long one - add input_free_device code into input_register_device
> call (http://lxr.free-electrons.com/source/drivers/input/input.c#L2114).
> 

The rules are pretty straightforward:

1. If you are using devm_input_allocate_device() you do not need to call
input_free_device() nor input_unregister_device()  - the core will
create a devres structure for freeing the device and if
input_register_device() succeeds it will also add a 2nd devres for
unregistering. This way the "normal" unwind is a 2-step process with
device is "half alive" and being able to survive input_event() calls
from IRQ handlers if they are still alive.

IOW  it should all "just work".

2. If you are using input_allocate_device() then you need to call
input_free_device() until you called input_register_device(), afterward
input_unregister_device() should be called.

Thanks.

-- 
Dmitry