From 2b7fcd18b15d9cc7b2e68deb77f4e0acfa904c41 Mon Sep 17 00:00:00 2001
From: Phil Elwell <phil@raspberrypi.com>
Date: Tue, 3 Nov 2020 10:13:48 +0000
Subject: [PATCH] Revert "mailbox: avoid timer start from callback"

This reverts commit 6dc15642c8b830d384fd3e6c9ea63144202b8932.

The Pi 400 shutdown/poweroff mechanism relies on being able to set
a GPIO on the expander in the pm_power_off handler, something that
requires two mailbox calls - GET_GPIO_STATE and SET_GPIO_STATE. A
recent kernel change introduces a reasonable possibility that the
GET call doesn't completes, and bisecting led to a commit from
October that changes the timer usage of the mailbox.

My theory is that there is a race condition in the new code that breaks
the poll timer, but that it normally goes unnoticed because subsequent
mailbox activity wakes it up again. The power-off mailbox calls happen
at a time when other subsystems have been shut down, so if one of them
fails then there is nothing to allow it to recover.

Revert 6dc15642 as (at least) a workaround.

See: https://github.com/raspberrypi/linux/issues/3941

Signed-off-by: Phil Elwell <phil@raspberrypi.com>
---
 drivers/mailbox/mailbox.c | 12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

--- a/drivers/mailbox/mailbox.c
+++ b/drivers/mailbox/mailbox.c
@@ -82,12 +82,9 @@ static void msg_submit(struct mbox_chan
 exit:
 	spin_unlock_irqrestore(&chan->lock, flags);
 
-	/* kick start the timer immediately to avoid delays */
-	if (!err && (chan->txdone_method & TXDONE_BY_POLL)) {
-		/* but only if not already active */
-		if (!hrtimer_active(&chan->mbox->poll_hrt))
-			hrtimer_start(&chan->mbox->poll_hrt, 0, HRTIMER_MODE_REL);
-	}
+	if (!err && (chan->txdone_method & TXDONE_BY_POLL))
+		/* kick start the timer immediately to avoid delays */
+		hrtimer_start(&chan->mbox->poll_hrt, 0, HRTIMER_MODE_REL);
 }
 
 static void tx_tick(struct mbox_chan *chan, int r)
@@ -125,10 +122,11 @@ static enum hrtimer_restart txdone_hrtim
 		struct mbox_chan *chan = &mbox->chans[i];
 
 		if (chan->active_req && chan->cl) {
-			resched = true;
 			txdone = chan->mbox->ops->last_tx_done(chan);
 			if (txdone)
 				tx_tick(chan, 0);
+			else
+				resched = true;
 		}
 	}
 
