[PATCH v2] drm/privacy-screen: honor acpi=off in detect_thinkpad_privacy_screen

[Tong Zhang <ztong0001@gmail.com>]

when acpi=off is provided in bootarg, kernel crash with

[    1.252739] BUG: kernel NULL pointer dereference, address: 0000000000000018
[    1.258308] Call Trace:
[    1.258490]  ? acpi_walk_namespace+0x147/0x147
[    1.258770]  acpi_get_devices+0xe4/0x137
[    1.258921]  ? drm_core_init+0xc0/0xc0 [drm]
[    1.259108]  detect_thinkpad_privacy_screen+0x5e/0xa8 [drm]
[    1.259337]  drm_privacy_screen_lookup_init+0xe/0xe85 [drm]

The reason is that acpi_walk_namespace expects acpi related stuff
initialized but in fact it wouldn't when acpi is set to off. In this case
we should honor acpi=off in detect_thinkpad_privacy_screen().

Signed-off-by: Tong Zhang <ztong0001@gmail.com>
---
v2: fix typo in previous commit -- my keyboard is eating letters 

 drivers/gpu/drm/drm_privacy_screen_x86.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/drm_privacy_screen_x86.c b/drivers/gpu/drm/drm_privacy_screen_x86.c
index a2cafb294ca6..e7aa74ad0b24 100644
--- a/drivers/gpu/drm/drm_privacy_screen_x86.c
+++ b/drivers/gpu/drm/drm_privacy_screen_x86.c
@@ -33,6 +33,9 @@ static bool __init detect_thinkpad_privacy_screen(void)
 	unsigned long long output;
 	acpi_status status;
 
+	if (acpi_disabled)
+		return false;
+
 	/* Get embedded-controller handle */
 	status = acpi_get_devices("PNP0C09", acpi_set_handle, NULL, &ec_handle);
 	if (ACPI_FAILURE(status) || !ec_handle)
-- 
2.25.1