[PATCH] lcd: Provide dummy functions if CONFIG_LCD_CLASS_DEVICE is not set

Provide dummy functions for LCD register()/unregister() if
CONFIG_LCD_CLASS_DEVICE is not set.

Signed-off-by: Alexander Shiyan <redacted>
---
 include/linux/lcd.h | 37 ++++++++++++++++++++++++++++++-------
 1 file changed, 30 insertions(+), 7 deletions(-)

diff --git a/include/linux/lcd.h b/include/linux/lcd.h
index 504f624..f1c94fd 100644
--- a/include/linux/lcd.h
+++ b/include/linux/lcd.h

@@ -110,14 +110,37 @@ static inline void lcd_set_power(struct lcd_device *ld, int power)
 	mutex_unlock(&ld->update_lock);
 }
 
-extern struct lcd_device *lcd_device_register(const char *name,
-	struct device *parent, void *devdata, struct lcd_ops *ops);
-extern struct lcd_device *devm_lcd_device_register(struct device *dev,
-	const char *name, struct device *parent,
+#if defined(CONFIG_LCD_CLASS_DEVICE) || defined(CONFIG_LCD_CLASS_DEVICE_MODULE)
+struct lcd_device *lcd_device_register(const char *name, struct device *parent,
 	void *devdata, struct lcd_ops *ops);
-extern void lcd_device_unregister(struct lcd_device *ld);
-extern void devm_lcd_device_unregister(struct device *dev,
-	struct lcd_device *ld);
+struct lcd_device *devm_lcd_device_register(struct device *dev,
+	const char *name, struct device *parent, void *devdata,
+	struct lcd_ops *ops);
+void lcd_device_unregister(struct lcd_device *ld);
+void devm_lcd_device_unregister(struct device *dev, struct lcd_device *ld);
+#else
+static inline struct lcd_device *lcd_device_register(const char *name,
+	struct device *parent, void *devdata, struct lcd_ops *ops)
+{
+	return ERR_PTR(-ENOSYS);
+}
+
+static inline struct lcd_device *devm_lcd_device_register(struct device *dev,
+	const char *name, struct device *parent, void *devdata,
+	struct lcd_ops *ops)
+{
+	return ERR_PTR(-ENOSYS);
+}
+
+static inline void lcd_device_unregister(struct lcd_device *ld)
+{
+}
+
+static inline void devm_lcd_device_unregister(struct device *dev,
+	struct lcd_device *ld)
+{
+}
+#endif
 
 #define to_lcd_device(obj) container_of(obj, struct lcd_device, dev)
 

-- 
1.8.3.2

On 13/03/14 09:31, Alexander Shiyan wrote:

Provide dummy functions for LCD register()/unregister() if
CONFIG_LCD_CLASS_DEVICE is not set.

Hmm, why do you want to do that? If a driver needs the LCD class, it
should depend on or select it.

 Tomi

On 13/03/14 10:48, Alexander Shiyan wrote:

Четверг, 13 марта 2014, 10:23 +02:00 от Tomi Valkeinen [off-list ref]:

quoted

On 13/03/14 09:31, Alexander Shiyan wrote:

quoted

Provide dummy functions for LCD register()/unregister() if
CONFIG_LCD_CLASS_DEVICE is not set.

Hmm, why do you want to do that? If a driver needs the LCD class, it
should depend on or select it.

I inspect my recent changes for the imxfb driver.
I use the LCD class for power management and contrast, nevertheless,
if it lack in the kernel this leads to an error.

So is the CONFIG_LCD_CLASS_DEVICE optional for imxfb? It works fine with
or without the LCD class support? Is there some reason to run it without
LCD class support?

Yes, we can choose the LCD_CLASS_DEVICE symbol for the imxfb driver,
but at the same time we must choose BACKLIGHT_LCD_SUPPORT.
I do not think it's a good way.

Why not?

In any case, I would like to revise the patch to use NULL as a result
if there is no support LCD_CLASS_DEVICE in the kernel.

Why do you want to run imxfb without LCD_CLASS_DEVICE? Isn't it simpler
to just depend on it?

Additionally, I have a plan to convert "menuconfig" entry for
BACKLIGHT_LCD_SUPPORT to the "menu".

Hmm. That does make sense, as I don't see BACKLIGHT_LCD_SUPPORT
affecting anything, except enabling the BL & LCD Kconfig menu.

However, many of the items in BL & LCD menu have, for some reason,
"default y" or "default m". So if you make BACKLIGHT_LCD_SUPPORT a menu,
it means all those subitems are always enabled. So there definitely will
be a side effect to that change.

I guess there's legacy reasons why many of the items are enabled by
default. It would make sense to me to have BACKLIGHT_LCD_SUPPORT as a
menu, as you suggest, and having all the subitems disabled by default.
But again, that would change the current behavior, which may or may not
cause issues.

 Tomi