linux-surface/patches/6.5/0006-surface-sam.patch

From b81f708b2a9b753fbd5f785be2a30c71befec1a9 Mon Sep 17 00:00:00 2001
From: Maximilian Luz <luzmaximilian@gmail.com>
Date: Tue, 3 Oct 2023 02:15:04 +0200
Subject: [PATCH] wip! serial: core: Disable runtime-suspend by default

Commit 84a9582fd203 ("serial: core: Start managing serial controllers to
enable runtime PM"), broke suspend on various Microsoft Surface devices.
In particular, devices with the Surface Aggregator Module (SAM) EC
connected via the Surface Serial Hub (SSH), a UART device.

The core issue is that any UART communication is blocked when the UART
port is in runtime suspend. Data sent during that time will be cached
and transferred only after the device has been runtime-resumed.
Unfortunately, any runtime PM transitions are blocked right before
entering normal suspend and only unblocked after resuming. This means,
that if we enter normal suspend when the port is runtime suspended, any
communication will be blocked until the device resumes.

Unfortunately, however, we need to tell the SAM EC when we are
suspending and resuming to quiesce / re-enable events, turn off the
keyboard backlight, and transition it to a lower power mode. This is
currently done in prepare()/complete() and suspend()/resume(). With the
commit mentioned above, these operations now time out, causing suspend
to fail.

As a temporary workaround: Disable runtime PM on the UART ports.

Signed-off-by: Maximilian Luz <luzmaximilian@gmail.com>
Patchset: surface-sam
---
 drivers/tty/serial/serial_port.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/tty/serial/serial_port.c b/drivers/tty/serial/serial_port.c
index 862423237007..6ceacea5e790 100644
--- a/drivers/tty/serial/serial_port.c
+++ b/drivers/tty/serial/serial_port.c
@@ -55,6 +55,8 @@ static int serial_port_probe(struct device *dev)
 	pm_runtime_set_autosuspend_delay(dev, SERIAL_PORT_AUTOSUSPEND_DELAY_MS);
 	pm_runtime_use_autosuspend(dev);
 
+	pm_runtime_forbid(dev);
+
 	return 0;
 }
 
-- 
2.42.0