drm: omapdrm: dss: Move initialization code from component bind to probe

drm: omapdrm: dss: Move initialization code from component bind to probe

BugLink: http://bugs.launchpad.net/bugs/1786352
[ Upstream commit 215003b4ae1d47035092fef73b6a22aa82037091 ]

There's no reason to delay initialization of most of the driver (such as
mapping memory I/O, getting clocks or enabling runtime PM) to the
component master bind handler.

This additionally fixes a real PM issue caused enabling runtime PM in
the bind handler.

The bind handler performs the following sequence of PM operations:

	pm_runtime_enable(dev);
	pm_runtime_get_sync(dev);

	... (access the hardware to read the device revision) ...

	pm_runtime_put_sync(dev);

If a failure occurs at this point, the error path calls
pm_runtime_disable() to balance the pm_runtime_enable() call.

To understand the problem, it should be noted that the bind handler is
called when one of the component registers itself, which happens in the
component's probe handler. Furthermore, as the components are children
of the DSS, the device core calls pm_runtime_get_sync() on the DSS
platform device before calling the component's probe handler. This
increases the DSS power usage count but doesn't runtime resume the
device, as runtime PM is disabled at that point.

The bind handler is thus called with runtime PM disabled, with the
device runtime suspended, but with the power usage count larger than 0.
The pm_runtime_get_sync() call will thus further increase the power
usage count and runtime resume the device. The pm_runtime_put_sync()
handler will decrease the power usage count to a non-zero value and will
thus not suspend the device. Finally, the pm_runtime_disable() call will
disable runtime PM, preventing the pm_runtime_put() call in the device
core from runtime suspending the device. The DSS device is thus left
powered on.

To fix this, move the initialization code from the bind handler to the
probe handler.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Sebastian Reichel <sebastian.reichel@collabora.co.uk>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>