[PATCH v4 11/13] firmware: arm_sdei: add support for CPU private events

Hi Will,

On 24/10/17 18:34, James Morse wrote:

On 18/10/17 18:19, Will Deacon wrote:

quoted

On Tue, Oct 17, 2017 at 06:44:30PM +0100, James Morse wrote:

quoted

Private SDE events are per-cpu, and need to be registered and enabled
on each CPU.

Hide this detail from the caller by adapting our {,un}register and
{en,dis}able calls to send an IPI to each CPU if the event is private.

CPU private events are unregistered when the CPU is powered-off, and
re-registered when the CPU is brought back online. This saves bringing
secondary cores back online to call private_reset() on shutdown, kexec
and resume from hibernate.

quoted

quoted

diff --git a/drivers/firmware/arm_sdei.c b/drivers/firmware/arm_sdei.c
index 28e4c4cbb16d..5598d9ba8b5d 100644
--- a/drivers/firmware/arm_sdei.c
+++ b/drivers/firmware/arm_sdei.c

@@ -610,6 +813,7 @@ static int sdei_device_freeze(struct device *dev)
 {
 	int err;
 
+	frozen = true;
 	err = sdei_event_unregister_all();

quoted

Are the release semantics from spin_unlock in sdei_event_unregister_all
sufficient for the ordering guarantees you need?

... ordering ...

The hotplug notifiers don't touch that lock, so at the first level: no.

It looks like I was relying on the cpu-hotplug code using stop-machine for its
work, and the spinlocks changing the pre-empt count for this to work. Which is
not something I want to debug if it changes!

I'll post a patch changing this bool to a more sensible atomic type.

Here I show my ignorance: atomic_t didn't do what I thought. But I do take the
spinlock inside the hotplug callback, so I'll move the variable in there.


Thanks,

James