Input: i8042 - break load dependency between atkbd/psmouse and i8042

As explained in 1407814240-4275-1-git-send-email-decui@microsoft.com we
have a hard load dependency between i8042 and atkbd which prevents
keyboard from working on Gen2 Hyper-V VMs.

> hyperv_keyboard invokes serio_interrupt(), which needs a valid serio
> driver like atkbd.c.  atkbd.c depends on libps2.c because it invokes
> ps2_command().  libps2.c depends on i8042.c because it invokes
> i8042_check_port_owner().  As a result, hyperv_keyboard actually
> depends on i8042.c.
>
> For a Generation 2 Hyper-V VM (meaning no i8042 device emulated), if a
> Linux VM (like Arch Linux) happens to configure CONFIG_SERIO_I8042=m
> rather than =y, atkbd.ko can't load because i8042.ko can't load(due to
> no i8042 device emulated) and finally hyperv_keyboard can't work and
> the user can't input: https://bugs.archlinux.org/task/39820
> (Ubuntu/RHEL/SUSE aren't affected since they use CONFIG_SERIO_I8042=y)

To break the dependency we move away from using i8042_check_port_owner()
and instead allow serio port owner specify a mutex that clients should use
to serialize PS/2 command stream.

Reported-by: Mark Laws <mdl@60hz.org>
Tested-by: Mark Laws <mdl@60hz.org>
Cc: stable@vger.kernel.org
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

2 files changed, 5 insertions, 21 deletions

diff --git a/drivers/input/serio/i8042.c b/drivers/input/serio/i8042.c
index 454195709a82..b4d34086e73f 100644
--- a/drivers/input/serio/i8042.c
+++ b/drivers/input/serio/i8042.c
@@ -1277,6 +1277,7 @@ static int __init i8042_create_kbd_port(void)
 	serio->start		= i8042_start;
 	serio->stop		= i8042_stop;
 	serio->close		= i8042_port_close;
+	serio->ps2_cmd_mutex	= &i8042_mutex;
 	serio->port_data	= port;
 	serio->dev.parent	= &i8042_platform_device->dev;
 	strlcpy(serio->name, "i8042 KBD port", sizeof(serio->name));
@@ -1373,21 +1374,6 @@ static void i8042_unregister_ports(void)
 	}
 }
 
-/*
- * Checks whether port belongs to i8042 controller.
- */
-bool i8042_check_port_owner(const struct serio *port)
-{
-	int i;
-
-	for (i = 0; i < I8042_NUM_PORTS; i++)
-		if (i8042_ports[i].serio == port)
-			return true;
-
-	return false;
-}
-EXPORT_SYMBOL(i8042_check_port_owner);
-
 static void i8042_free_irqs(void)
 {
 	if (i8042_aux_irq_registered)
diff --git a/drivers/input/serio/libps2.c b/drivers/input/serio/libps2.c
index 316f2c897101..83e9c663aa67 100644
--- a/drivers/input/serio/libps2.c
+++ b/drivers/input/serio/libps2.c
@@ -56,19 +56,17 @@ EXPORT_SYMBOL(ps2_sendbyte);
 
 void ps2_begin_command(struct ps2dev *ps2dev)
 {
-	mutex_lock(&ps2dev->cmd_mutex);
+	struct mutex *m = ps2dev->serio->ps2_cmd_mutex ?: &ps2dev->cmd_mutex;
 
-	if (i8042_check_port_owner(ps2dev->serio))
-		i8042_lock_chip();
+	mutex_lock(m);
 }
 EXPORT_SYMBOL(ps2_begin_command);
 
 void ps2_end_command(struct ps2dev *ps2dev)
 {
-	if (i8042_check_port_owner(ps2dev->serio))
-		i8042_unlock_chip();
+	struct mutex *m = ps2dev->serio->ps2_cmd_mutex ?: &ps2dev->cmd_mutex;
 
-	mutex_unlock(&ps2dev->cmd_mutex);
+	mutex_unlock(m);
 }
 EXPORT_SYMBOL(ps2_end_command);