[PATCH v2 03/16] backlight: add backlight_is_blank()

[Sam Ravnborg]

The backlight support has two properties that express the state:
- power
- state

It is un-documented and easy to get wrong.
Add backlight_is_blank() helper to make it simpler for drivers
to get the check of the state correct.

A lot of drivers also includes checks for fb_blank.
This check is redundant when the state is checked
and thus not needed in this helper function.
But added anyway to avoid introducing subtle bug
due to the creative use in some drivers.

Rolling out this helper to all relevant backlight drivers
will eliminate almost all accesses to fb_blank.

v2:
  - Added fb_blank condition (Daniel)

Signed-off-by: Sam Ravnborg <sam at ravnborg.org>
Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
Cc: Lee Jones <lee.jones at linaro.org>
Cc: Daniel Thompson <daniel.thompson at linaro.org>
Cc: Jingoo Han <jingoohan1 at gmail.com>
---
 include/linux/backlight.h | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/include/linux/backlight.h b/include/linux/backlight.h
index c7d6b2e8c3b5..a0a083b35c47 100644
--- a/include/linux/backlight.h
+++ b/include/linux/backlight.h
@@ -175,6 +175,25 @@ static inline void backlight_put(struct backlight_device *bd)
 		put_device(&bd->dev);
 }
 
+/**
+ * backlight_is_blank - Return true if display is expected to be blank
+ * @bd: the backlight device
+ *
+ * Display is expected to be blank if any of these is true::
+ *
+ *   1) if power in not UNBLANK
+ *   2) if fb_blank is not UNBLANK
+ *   3) if state indicate BLANK or SUSPENDED
+ *
+ * Returns true if display is expected to be blank, false otherwise.
+ */
+static inline bool backlight_is_blank(struct backlight_device *bd)
+{
+	return bd->props.power != FB_BLANK_UNBLANK ||
+	       bd->props.fb_blank != FB_BLANK_UNBLANK ||
+	       bd->props.state & (BL_CORE_SUSPENDED | BL_CORE_FBBLANK);
+}
+
 extern struct backlight_device *backlight_device_register(const char *name,
 	struct device *dev, void *devdata, const struct backlight_ops *ops,
 	const struct backlight_properties *props);
-- 
2.25.1