Thank you for your comments.

it is a good idea that lcd driver registers interfaces to lcd class
and backlight class.
but I think for AMOLED LCD Panel, backlight couldn't be real device so
power on/off
for backlight device doesn't make sense.

I had tried lcd driver registers interfaces to lcd class and backlight
class as you said.
and also backlight fake driver as Pavel said.

but I thought to use my patch is more simple and effective.
of course, this patch has a problem that it has different path from
backlight class
for controlling brightness.

how about creating symbolic link file for competiability?

Best Regards,
InKi Dae.

2009/11/10 Richard Purdie [off-list ref]:

On Mon, 2009-11-02 at 17:50 +0900, InKi Dae wrote:

quoted

This patch adds brightness feature to lcd class.
(kernel/driver/video/backlight/lcd.c)

In the past, most of the lcd panels for embedded system was TFT-LCD
Panel needing backlight device.
But now AMOLED LCD Panel appeared so we should consider brightness
control for AMOLED Panel.

For the time being, I used backlight fake driver for brightness
control of AMOLED LCD Panel.
But this way is not good, so I propose to add brightness feature to lcd class.

For this, I attached patch file and if my proposal is approved
Then I will send s6e63m0 and tl2796 AMOLED lcd panel driver based on
lcd class modified soon.

Pavel has a good point but let me try and explain it differently.

The point of the backlight class is to expose a backlight brightness
control to userspace in a consistent well defined way. Anyone wishing to
write a piece of software to control the brightness of a backlight then
only needs to support *one* interface.

It is entirely accepted and normal that multiple "class" devices may
appear in userspace for one piece of physical hardware.

Your patch duplicates a userspace API and means any backlight
application would have to look for *two* different interfaces. This is
unacceptable.

Why can't your driver just register a backlight interface and an LCD
interface? I'd imagine your backlight and LCD can be powered on/off
separately too.

Please also cc: the backlight/lcd maintainer (me) on backlight/lcd
patches in future.

Andrew: Can you drop that patch from -mm please as I'm not convinced we
need two backlight brightness interfaces around...

Cheers,

Richard