[PATCH] Input: i8042 - Allow insmod to succeed on devices without an i8042 controller

[Hans de Goede <hdegoede@redhat.com>]

The i8042 module exports several symbols which may be used by other
modules.

Before this commit it would refuse to load (when built as a module itself)
on systems without an i8042 controller.

This is a problem specifically for the asus-nb-wmi module. Many Asus
laptops support the Asus WMI interface. Some of them have an i8042
controller and need to use i8042_install_filter() to filter some kbd
events. Other models do not have an i8042 controller (e.g. they use an
USB attached kbd).

Before this commit the asus-nb-wmi driver could not be loaded on Asus
models without an i8042 controller, when the i8042 code was built as
a module (as Arch Linux does) because the module_init function of the
i8042 module would fail with -ENODEV and thus the i8042_install_filter
symbol could not be loaded.

This commit fixes this by exiting from module_init with a return code
of 0 if no controller is found.  It also adds a i8042_present bool to
make the module_exit function a no-op in this case and also adds a
check for i8042_present to the exported i8042_command function.

The latter i8042_present check should not really be necessary because
when builtin that function can already be used on systems without
an i8042 controller, but better safe then sorry.

Reported-and-tested-by: Marius Iacob <themariusus@gmail.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
---
 drivers/input/serio/i8042.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/drivers/input/serio/i8042.c b/drivers/input/serio/i8042.c
index d3eda48032e3..944cbb519c6d 100644
--- a/drivers/input/serio/i8042.c
+++ b/drivers/input/serio/i8042.c
@@ -122,6 +122,7 @@ module_param_named(unmask_kbd_data, i8042_unmask_kbd_data, bool, 0600);
 MODULE_PARM_DESC(unmask_kbd_data, "Unconditional enable (may reveal sensitive data) of normally sanitize-filtered kbd data traffic debug log [pre-condition: i8042.debug=1 enabled]");
 #endif
 
+static bool i8042_present;
 static bool i8042_bypass_aux_irq_test;
 static char i8042_kbd_firmware_id[128];
 static char i8042_aux_firmware_id[128];
@@ -343,6 +344,9 @@ int i8042_command(unsigned char *param, int command)
 	unsigned long flags;
 	int retval;
 
+	if (!i8042_present)
+		return -1;
+
 	spin_lock_irqsave(&i8042_lock, flags);
 	retval = __i8042_command(param, command);
 	spin_unlock_irqrestore(&i8042_lock, flags);
@@ -1612,12 +1616,15 @@ static int __init i8042_init(void)
 
 	err = i8042_platform_init();
 	if (err)
-		return err;
+		return (err == -ENODEV) ? 0 : err;
 
 	err = i8042_controller_check();
 	if (err)
 		goto err_platform_exit;
 
+	/* Set this before creating the dev to allow i8042_command to work right away */
+	i8042_present = true;
+
 	pdev = platform_create_bundle(&i8042_driver, i8042_probe, NULL, 0, NULL, 0);
 	if (IS_ERR(pdev)) {
 		err = PTR_ERR(pdev);
@@ -1636,6 +1643,9 @@ static int __init i8042_init(void)
 
 static void __exit i8042_exit(void)
 {
+	if (!i8042_present)
+		return;
+
 	platform_device_unregister(i8042_platform_device);
 	platform_driver_unregister(&i8042_driver);
 	i8042_platform_exit();
-- 
2.28.0