We need to add a dummy smc call to the cpuidle wakeup path to force the
ROM code to save the return address after MMU is enabled again. This is
needed to prevent random hangs on secure devices like droid4.

Otherwise the system will eventually hang when entering deeper SoC idle
states with the core and mpu domains in open-switch retention (OSWR).
The hang happens as the ROM code tries to use the earlier physical return
address set by omap-headsmp.S with MMU off while waking up CPU1 again.

The hangs started happening in theory already with commit caf8c87d
("ARM: OMAP2+: Allow core oswr for omap4"), but in practise the issue went
unnoticed as various drivers were often blocking any deeper idle states
with hardware autoidle features.

This patch is based on an earlier TI Linux kernel tree commit 92f0b3028d9e
("OMAP4: PM: update ROM return address for OSWR and OFF") written by
Carlos Leija <cileija@ti.com>, Praneeth Bajjuri <praneeth@ti.com>, and
Bryan Buckley <bryan.buckley@ti.com>. A later version of the patch was
updated to use CPU_PM notifiers by Tero Kristo <t-kristo@ti.com>.
Signed-off-by: Carlos Leija <cileija@ti.com>
Signed-off-by: Praneeth Bajjuri <praneeth@ti.com>
Signed-off-by: Bryan Buckley <bryan.buckley@ti.com>
Signed-off-by: Tero Kristo <t-kristo@ti.com>
Fixes: caf8c87d ("ARM: OMAP2+: Allow core oswr for omap4")
Reported-by: Carl Philipp Klemm <philipp@uvos.xyz>
Reported-by: Merlijn Wajer <merlijn@wizzup.org>
Cc: Ivan Jelincic <parazyd@dyne.org>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: Sebastian Reichel <sre@kernel.org>
Cc: Tero Kristo <kristo@kernel.org>
[tony@atomide.com: updated to apply, updated description]
Signed-off-by: Tony Lindgren <tony@atomide.com>