spmi: pmic-arb: clear the latched status of the interrupt

spmi: pmic-arb: clear the latched status of the interrupt

PMIC interrupts each have an internal latched status bit which is
not visible from any register.  This status bit is set as soon as
the conditions specified in the interrupt type and polarity
registers are met even if the interrupt is not enabled.  When it
is set, nothing else changes within the PMIC and no interrupt
notification packets are sent.  If the internal latched status
bit is set when an interrupt is enabled, then the value is
immediately propagated into the interrupt latched status register
and an interrupt notification packet is sent out from the PMIC
over SPMI.

This PMIC hardware behavior can lead to a situation where the
handler for a level triggered interrupt is called immediately
after enable_irq() is called even though the interrupt physically
triggered while it was disabled within the genirq framework.
This situation takes place if the the interrupt fires twice after
calling disable_irq().  The first time it fires, the level flow
handler will mask and disregard it.  Unfortunately, the second
time it fires, the internal latched status bit is set within the
PMIC and no further notification is received.  When enable_irq()
is called later, the interrupt is unmasked (enabled in the PMIC)
which results in the PMIC immediately sending an interrupt
notification packet out over SPMI.  This breaks the semantics
of level triggered interrupts within the genirq framework since
they should be completely ignored while disabled.

The PMIC internal latched status behavior also affects how
interrupts are treated during suspend.  While entering suspend,
all interrupts not specified as wakeup mode are masked.  Upon
resume, these interrupts are unmasked.  Thus if any of the
non-wakeup PMIC interrupts fired while the system was suspended,
then the PMIC will send interrupt notification packets out via
SPMI as soon as they are unmasked during resume.  This behavior
violates genirq semantics as well since non-wakeup interrupts
should be completely ignored during suspend.

Modify the qpnpint_irq_unmask() function so that the interrupt
latched status clear register is written immediately before the
interrupt enable register.  This clears the internal latched
status bit of the interrupt so that it cannot trigger spuriously
immediately upon being enabled.

Also, while resuming an irq, an unmask could be called even if it
was not previously masked.  So, before writing these registers,
check if the interrupt is already enabled within the PMIC. If it
is, then no further register writes are required.  This
condition check ensures that a valid latched status register bit
is not cleared until it is properly handled.

Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>
Signed-off-by: Kiran Gunda <kgunda@codeaurora.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>