acpi: add a way to promote/demote vendor backlight drivers

Instead of adding a big blacklist in video_detect.c to set
ACPI_VIDEO_BACKLIGHT_DMI_VENDOR correctly, let external modules
promote or demote themselves when they know the generic video
module won't work.

Currently drivers where using acpi_video_unregister() directly
but:
- That didn't respect any acpi_backlight=[video|vendor] parameter
  provided by the user.
- Any later call to acpi_video_register() would still re-load the
  generic video module (and some gpu drivers are doing that).

This patch fix those two issues.

Signed-off-by: Corentin Chary <corentin.chary@gmail.com>
Signed-off-by: Matthew Garrett <mjg@redhat.com>

drivers/acpi/video_detect.c

@@ -182,8 +182,7 @@ long acpi_video_get_capabilities(acpi_handle graphics_handle)
 }
 EXPORT_SYMBOL(acpi_video_get_capabilities);
 
-/* Returns true if video.ko can do backlight switching */
-int acpi_video_backlight_support(void)
+static void acpi_video_caps_check(void)
 {
 	/*
 	 * We must check whether the ACPI graphics device is physically plugged
@@ -191,6 +190,34 @@ int acpi_video_backlight_support(void)
 	 */
 	if (!acpi_video_caps_checked)
 		acpi_video_get_capabilities(NULL);
+}
+
+/* Promote the vendor interface instead of the generic video module.
+ * This function allow DMI blacklists to be implemented by externals
+ * platform drivers instead of putting a big blacklist in video_detect.c
+ * After calling this function you will probably want to call
+ * acpi_video_unregister() to make sure the video module is not loaded
+ */
+void acpi_video_dmi_promote_vendor(void)
+{
+	acpi_video_caps_check();
+	acpi_video_support |= ACPI_VIDEO_BACKLIGHT_DMI_VENDOR;
+}
+EXPORT_SYMBOL(acpi_video_dmi_promote_vendor);
+
+/* To be called when a driver who previously promoted the vendor
+ * interface */
+void acpi_video_dmi_demote_vendor(void)
+{
+	acpi_video_caps_check();
+	acpi_video_support &= ~ACPI_VIDEO_BACKLIGHT_DMI_VENDOR;
+}
+EXPORT_SYMBOL(acpi_video_dmi_demote_vendor);
+
+/* Returns true if video.ko can do backlight switching */
+int acpi_video_backlight_support(void)
+{
+	acpi_video_caps_check();
 
 	/* First check for boot param -> highest prio */
 	if (acpi_video_support & ACPI_VIDEO_BACKLIGHT_FORCE_VENDOR)

include/linux/acpi.h

@@ -190,6 +190,8 @@ extern bool wmi_has_guid(const char *guid);
 
 extern long acpi_video_get_capabilities(acpi_handle graphics_dev_handle);
 extern long acpi_is_video_device(struct acpi_device *device);
+extern void acpi_video_dmi_promote_vendor(void);
+extern void acpi_video_dmi_demote_vendor(void);
 extern int acpi_video_backlight_support(void);
 extern int acpi_video_display_switch_support(void);
 
@@ -205,6 +207,14 @@ static inline long acpi_is_video_device(struct acpi_device *device)
 	return 0;
 }
 
+static inline void acpi_video_dmi_promote_vendor(void)
+{
+}
+
+static inline void acpi_video_dmi_demote_vendor(void)
+{
+}
+
 static inline int acpi_video_backlight_support(void)
 {
 	return 0;