dmtimer: ack pending interrupt during suspend on am335x/am437x?

[Drew Fustini]

Hello Daniel, Tony suggested I mail you along with the list to get
feedback. I'm attempting to upstream these two patches [1][2] from
ti-linux-5.4.y for arch/arm/mach-omap2/timer.c:
96f4c6e2ba8a ("ARM: OMAP2+: timer: Ack pending interrupt during suspend")
7ae7dd5f8272 ("ARM: OMAP2+: timer: Extend pending interrupt ACK for gic")

On the TI AM335x and AM437x SoCs, it is possible for a late interrupt to
be generated which will cause a suspend failure. The first patch makes
omap_clkevt_idle() ack the irq both in the timer peripheral register
and in the interrupt controller to avoid the issue.

On AM437x only, the GIC cannot be directly acked using only the irqchip
calls. To workaround that, the second patch maps the GIC_CPU_BASE and
reads the GIC_CPU_INTACK register before calling irq_eoi to properly ack
the late timer interrupts that show up during suspend.

However, Tony removed most of arch/arm/mach-omap2/timer.c with:
2ee04b88547a ("ARM: OMAP2+: Drop old timer code for dmtimer and 32k counter")

The timers are now implemented in drivers/clocksource/timer-ti-dm.c and
drivers/clocksource/timer-ti-dm-systimer.c. The function
dmtimer_clocksource_suspend() disables the dmtimer and clock but does
not ack any interrupts.

Tony suggested the right place to ack the interrupt during suspend is
in CPU_CLUSTER_PM_ENTER inside omap_timer_context_notifier().

Do you think that would be an acceptable approach?

Thank you,
Drew

[1] https://git.ti.com/cgit/ti-linux-kernel/ti-linux-kernel/commit/?h=ti-linux-5.4.y&id=96f4c6e2ba8a
[2] https://git.ti.com/cgit/ti-linux-kernel/ti-linux-kernel/commit/?h=ti-linux-5.4.y&id=7ae7dd5f8272