linux-kernel - [PATCH 1/2] serial: omap: fix runtime-pm handling on unbind

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Date:   Mon, 10 Apr 2017 11:21:38 +0200
From:   Johan Hovold <johan@...nel.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Jiri Slaby <jslaby@...e.com>, linux-serial@...r.kernel.org,
        linux-omap@...r.kernel.org, linux-kernel@...r.kernel.org,
        Johan Hovold <johan@...nel.org>,
        Felipe Balbi <balbi@...nel.org>,
        Santosh Shilimkar <santosh.shilimkar@...com>,
        Tony Lindgren <tony@...mide.com>
Subject: [PATCH 1/2] serial: omap: fix runtime-pm handling on unbind

An unbalanced and misplaced synchronous put was used to suspend the
device on driver unbind, something which with a likewise misplaced
pm_runtime_disable leads to external aborts when an open port is being
removed.

Unhandled fault: external abort on non-linefetch (0x1028) at 0xfa024010
...
[<c046e760>] (serial_omap_set_mctrl) from [<c046a064>] (uart_update_mctrl+0x50/0x60)
[<c046a064>] (uart_update_mctrl) from [<c046a400>] (uart_shutdown+0xbc/0x138)
[<c046a400>] (uart_shutdown) from [<c046bd2c>] (uart_hangup+0x94/0x190)
[<c046bd2c>] (uart_hangup) from [<c045b760>] (__tty_hangup+0x404/0x41c)
[<c045b760>] (__tty_hangup) from [<c045b794>] (tty_vhangup+0x1c/0x20)
[<c045b794>] (tty_vhangup) from [<c046ccc8>] (uart_remove_one_port+0xec/0x260)
[<c046ccc8>] (uart_remove_one_port) from [<c046ef4c>] (serial_omap_remove+0x40/0x60)
[<c046ef4c>] (serial_omap_remove) from [<c04845e8>] (platform_drv_remove+0x34/0x4c)

Fix this up by resuming the device before deregistering the port and by
suspending and disabling runtime pm only after the port has been
removed.

Also make sure to disable autosuspend before disabling runtime pm so
that the usage count is balanced and device actually suspended before
returning.

Note that due to a negative autosuspend delay being set in probe, the
unbalanced put would actually suspend the device on first driver unbind,
while rebinding and again unbinding would result in a negative
power.usage_count.

Fixes: 7e9c8e7dbf3b ("serial: omap: make sure to suspend device before remove")
Cc: Felipe Balbi <balbi@...nel.org>
Cc: Santosh Shilimkar <santosh.shilimkar@...com>
Cc: Tony Lindgren <tony@...mide.com>
Signed-off-by: Johan Hovold <johan@...nel.org>
---
 drivers/tty/serial/omap-serial.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/serial/omap-serial.c b/drivers/tty/serial/omap-serial.c
index 6c6f82ad8d5c..8c2086e14b51 100644
--- a/drivers/tty/serial/omap-serial.c
+++ b/drivers/tty/serial/omap-serial.c
@@ -1780,9 +1780,13 @@ static int serial_omap_remove(struct platform_device *dev)
 {
 	struct uart_omap_port *up = platform_get_drvdata(dev);
 
+	pm_runtime_get_sync(up->dev);
+
+	uart_remove_one_port(&serial_omap_reg, &up->port);
+
+	pm_runtime_dont_use_autosuspend(up->dev);
 	pm_runtime_put_sync(up->dev);
 	pm_runtime_disable(up->dev);
-	uart_remove_one_port(&serial_omap_reg, &up->port);
 	pm_qos_remove_request(&up->pm_qos_request);
 	device_init_wakeup(&dev->dev, false);
 
-- 
2.12.2