[PATCH] mfd: twl-core: export twl_get_regmap

[Nicolae Rosia]

On Mon, Nov 21, 2016 at 11:31 AM, Russell King - ARM Linux
<linux at armlinux.org.uk> wrote:
> Passing data between drivers using *_set_drvdata() is a layering
> violation:
>
> 1. Driver data is supposed to be driver private data associated with
>    the currently bound driver.
> 2. The driver data pointer is NULL'd when the driver unbinds from the
>    device.  See __device_release_driver() and the
>    dev_set_drvdata(dev, NULL).
> 3. It will break with CONFIG_DEBUG_TEST_DRIVER_REMOVE enabled for a
>    similar reason to (2).
>
> So, do not pass data between drivers using *_set_drvdata() - any
> examples in the kernel already are founded on bad practice, are
> fragile, and are already broken for some kernel configurations.
After inspecting mfd_add_device, it seems that it creates a
platform_device which has the parent set to the driver calling the
function.
Isn't module unloading forbidden if there is a parent->child
relationship in place and you're removing the parent?
What should be the best practice to share data between drivers?
Reference counted data?
In the case of TWL, the twl-core is just a simple container for
regmaps - all other "sub devices" are using those regmaps to access
the I2C device's registers, it makes no sense to remove the parent
driver since it does *nothing*.