[PATCH] mfd: twl-core: export twl_get_regmap

[Russell King - ARM Linux]

On Mon, Nov 21, 2016 at 09:23:39AM +0000, Lee Jones wrote:
> It's common place to pass shared resources such as 'regmap' though
> device data.  You can find many examples of *__set_drvdata throughout
> the kernel.

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.

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