On 09/04/2026 4:54 pm, Leo Yan wrote:
On Thu, Apr 09, 2026 at 11:52:06AM +0100, James Clark wrote:
On 05/04/2026 4:02 pm, Leo Yan wrote:
From: Yabin Cui yabinc@google.com
TRBE context can be lost when a CPU enters low power states. If a trace source is restored while TRBE is not, tracing may run without an active sink, which can lead to hangs on some devices (e.g., Pixel 9).
Can't this still happen if saving the source times out on "wait for TRCSTATR.IDLE to go up"?
That would make coresight_pm_save() exit early, not saving the active TRBE state. Then when coresight_pm_restore() is called it restores a stale inactive sink, then enables the source again which is the state that can hang.
Hmm... I don't expect this to happen anyway.
If CPU PM enter fails and returns an error, it will bail out early of the idle flow and the CPU will not proceed entering low power states; therefore, the restore flow does not exist.
Thanks, Leo
Ah ok I missed that that was how it behaved. I didn't realise that an error here would prevent the restore from being called. That makes my other comments redundant as well then.