ACPI: thinkpad-acpi: prefer standard ACPI backlight level control

Newer Lenovo BIOSes support the standard ACPI backlight brightness
interface (_BCM, _BQC, _BCL).  It should be used instead of the native
thinkpad backlight brightness control interface when possible.

This patch disables the native brightness support in the driver by default
when we detect that the standard ACPI interface is available.  The local
admin can still enable it using the module parameter "brightness_enable".

Note that we need to detect the standard ACPI backlight interface only in
boxes for which we would load the native backlight interface in the first
place, and that no ThinkPad BIOS has _BCL but misses the other methods, so
the detection routines can be really simple.

Signed-off-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Signed-off-by: Len Brown <len.brown@intel.com>

1 files changed, 39 insertions, 0 deletions

diff --git a/drivers/misc/thinkpad_acpi.c b/drivers/misc/thinkpad_acpi.c
index 56a21e6b80a9..109bd2750439 100644
--- a/drivers/misc/thinkpad_acpi.c
+++ b/drivers/misc/thinkpad_acpi.c
@@ -3174,6 +3174,39 @@ static int __init brightness_check_levels(void)
 	return (ACPI_SUCCESS(status) && found_node != NULL);
 }
 
+static acpi_status __init brightness_find_bcl(acpi_handle handle, u32 lvl,
+					void *context, void **rv)
+{
+	char name[ACPI_PATH_SEGMENT_LENGTH];
+	struct acpi_buffer buffer = { sizeof(name), &name };
+
+	if (ACPI_SUCCESS(acpi_get_name(handle, ACPI_SINGLE_NAME, &buffer)) &&
+	    !strncmp("_BCL", name, sizeof(name) - 1)) {
+		*rv = handle;
+		return AE_CTRL_TERMINATE;
+	} else {
+		return AE_OK;
+	}
+}
+
+static int __init brightness_check_std_acpi_support(void)
+{
+	int status;
+	void *found_node = NULL;
+
+	if (!vid_handle) {
+		IBM_ACPIHANDLE_INIT(vid);
+	}
+	if (!vid_handle)
+		return 0;
+
+	/* Search for a _BCL method, but don't execute it */
+	status = acpi_walk_namespace(ACPI_TYPE_METHOD, vid_handle, 3,
+	                             brightness_find_bcl, NULL, &found_node);
+
+	return (ACPI_SUCCESS(status) && found_node != NULL);
+}
+
 static int __init brightness_init(struct ibm_init_struct *iibm)
 {
 	int b;
@@ -3186,6 +3219,12 @@ static int __init brightness_init(struct ibm_init_struct *iibm)
 		dbg_printk(TPACPI_DBG_INIT,
 		           "brightness support disabled by module parameter\n");
 		return 1;
+	} else if (brightness_enable > 1) {
+		if (brightness_check_std_acpi_support()) {
+			printk(IBM_NOTICE
+			       "standard ACPI backlight interface available, not loading native one...\n");
+			return 1;
+		}
 	}
 
 	if (!brightness_mode) {