OMAP3+: SR: ensure pm-runtime callbacks can be invoked with IRQs disabled

SmartReflex should be disabled while entering low power mode due to
a) SmartReflex values are not defined for retention voltage, further
b) with SmartReflex enabled, if CPU enters lower c-states, FSM will try
to bump the voltage to current OPP's voltage for which it has entered c-state;
hence SmartReflex needs to be disabled for MPU, CORE and IVA voltage
domains in idle path before enabling auto retention voltage achievement
on the device.

However, since the current pm_runtime setup for SmartReflex devices are
setup to allow callbacks to be invoked with interrupts enabled, calling
SmartReflex enable/disable from other contexts such as idle paths
where preemption is disabled causes warnings such as the following
indicating of a potential race.
[   82.023895] [<c04d079c>] (__irq_svc+0x3c/0x120) from [<c04d0484>] (_raw_spin_unlock_irq+0x28/0x2c)
[   82.023895] [<c04d0484>] (_raw_spin_unlock_irq+0x28/0x2c) from [<c0323234>] (rpm_callback+0x4c/0x68)
[   82.023956] [<c0323234>] (rpm_callback+0x4c/0x68) from [<c0323f7c>] (rpm_resume+0x338/0x53c)
[   82.023956] [<c0323f7c>] (rpm_resume+0x338/0x53c) from [<c03243f4>] (__pm_runtime_resume+0x48/0x60)
[   82.023986] [<c03243f4>] (__pm_runtime_resume+0x48/0x60) from [<c008aee0>] (sr_enable+0xa8/0x19c)
[   82.023986] [<c008aee0>] (sr_enable+0xa8/0x19c) from [<c008b2fc>] (omap_sr_enable+0x50/0x90)
[   82.024017] [<c008b2fc>] (omap_sr_enable+0x50/0x90) from [<c00888c0>] (omap4_enter_sleep+0x138/0x168)

Instead, we use pm_runtime_irq_safe to tell the PM core that callbacks can be
invoked in interrupt disabled contexts.
Acked-by: Rajendra Nayak <rnayak@ti.com>
Signed-off-by: Nishanth Menon <nm@ti.com>
[khilman@ti.com: minor changelog edits]
Signed-off-by: Kevin Hilman <khilman@ti.com>

arch/arm/mach-omap2/smartreflex.c

@@ -860,6 +860,7 @@ static int __init omap_sr_probe(struct platform_device *pdev)
 	irq = platform_get_resource(pdev, IORESOURCE_IRQ, 0);
 
 	pm_runtime_enable(&pdev->dev);
+	pm_runtime_irq_safe(&pdev->dev);
 
 	sr_info->pdev = pdev;
 	sr_info->srid = pdev->id;