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

As explained in [e-mail] 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 <[e-mail]>
Tested-by: Mark Laws <[e-mail]>
Cc: [e-mail]
Signed-off-by: Dmitry Torokhov <[e-mail]>

drivers/input/serio/i8042.c

···
 	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));
···
 		}
 	}
 }
-
-/*
- * 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)
 {

drivers/input/serio/libps2.c

···
 
 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);
 

include/linux/i8042.h

···
 void i8042_lock_chip(void);
 void i8042_unlock_chip(void);
 int i8042_command(unsigned char *param, int command);
-bool i8042_check_port_owner(const struct serio *);
 int i8042_install_filter(bool (*filter)(unsigned char data, unsigned char str,
 					struct serio *serio));
 int i8042_remove_filter(bool (*filter)(unsigned char data, unsigned char str,
···
 static inline int i8042_command(unsigned char *param, int command)
 {
 	return -ENODEV;
-}
-
-static inline bool i8042_check_port_owner(const struct serio *serio)
-{
-	return false;
 }
 
 static inline int i8042_install_filter(bool (*filter)(unsigned char data, unsigned char str,

include/linux/serio.h

···
 
 	struct serio_device_id id;
 
-	spinlock_t lock;		/* protects critical sections from port's interrupt handler */
+	/* Protects critical sections from port's interrupt handler */
+	spinlock_t lock;
 
 	int (*write)(struct serio *, unsigned char);
 	int (*open)(struct serio *);
···
 	void (*stop)(struct serio *);
 
 	struct serio *parent;
-	struct list_head child_node;	/* Entry in parent->children list */
+	/* Entry in parent->children list */
+	struct list_head child_node;
 	struct list_head children;
-	unsigned int depth;		/* level of nesting in serio hierarchy */
+	/* Level of nesting in serio hierarchy */
+	unsigned int depth;
 
-	struct serio_driver *drv;	/* accessed from interrupt, must be protected by serio->lock and serio->sem */
-	struct mutex drv_mutex;		/* protects serio->drv so attributes can pin driver */
+	/*
+	 * serio->drv is accessed from interrupt handlers; when modifying
+	 * caller should acquire serio->drv_mutex and serio->lock.
+	 */
+	struct serio_driver *drv;
+	/* Protects serio->drv so attributes can pin current driver */
+	struct mutex drv_mutex;
 
 	struct device dev;
 
 	struct list_head node;
+
+	/*
+	 * For use by PS/2 layer when several ports share hardware and
+	 * may get indigestion when exposed to concurrent access (i8042).
+	 */
+	struct mutex *ps2_cmd_mutex;
 };
 #define to_serio_port(d)	container_of(d, struct serio, dev)