On 4/19/07, Cornelia Huck <[email protected]> wrote:
On Wed, 18 Apr 2007 12:41:36 -0400,
"Dmitry Torokhov" <[email protected]> wrote:
> I am still do not understand why this is needed. Would it not be
> simplier just to use a reference to struct device instead of embedding
> it in a larger structure if their lifetimes are different and one does
> not have a subsystem that takes care of releasing logic.
Why are their lifetimes different? Usually, if I hold on to the device,
I also want to be able to use the structure that embeds the device.
Because they are managed by 2 different entities. the struct device
objects are managed by device core and driver-specific objects are
managed by their respective driver.
> Pretty much drivers have 2 options:
>
> struct my_device {
> void *private_data;
> struct device dev;
> };
>
> In this case ->release must live in a subsystem code; individual
> drivers kfree(my_dev->private) and do any additional cleanup after
> calling device_unregister(&my_dev->dev);
They must do this in the ->remove callback.
Why? If the driver truly stops hardware then any driver-specific data
is not needed. With sysfs severing access to removed attributes there
is no need to gave "global release", cleanup can be done in stages.
>
> Second option:
>
> struct my_device {
> type member1;
> type member2;
>
> struct device *dev;
> };
>
> dev is coming from _device_create(). Driver core takes care of
> releasing dev structure; driver does cleanup of my_device.
device_create() would need to not expect a class then, or it's not
universally usable. Also, the driver would need a method to get back
from the device to my_device. We're practically back at the first
option again, only that now the ->release function is sitting in the
driver core instead of the subsystem.
To a degree.
--
Dmitry
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