The intensity of the backlight can be varied from a range of
max_brightness to zero. Though most, if not all the pwm based backlight
devices start flickering at lower brightness value. And also for each
device there exists a brightness value below which the backlight appears
to be turned off though the value is not equal to zero.
If the range of brightness for a device is from zero to max_brightness. A
graph is plotted for brightness Vs intensity for the pwm based backlight
device has to be a linear graph.
intensity
| /
| /
| /
|/
---------
0 max_brightness
But pratically on measuring the above we note that the intensity of
backlight goes to zero(OFF) when the value in not zero almost nearing to
zero(some x%). so the graph looks like
intensity
| /
| /
| /
| |
------------
0 x max_brightness
In order to overcome this drawback knowing this x% i.e nothing but the low
threshold beyond which the backlight is off and will have no effect, the
brightness value is being offset by the low threshold value(retaining the
linearity of the graph). Now the graph becomes
intensity
| /
| /
| /
| /
-------------
0 max_brightness
With this for each and every digit increment in the brightness from zero
there is a change in the intensity of backlight. Devices having this
behaviour can set the low threshold brightness(lth_brightness) and pass
the same as platform data else can have it as zero.
[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Arun Murthy <arun.murthy@stericsson.com>
Acked-by: Linus Walleij <linus.walleij@stericsson.com>
Acked-by: Richard Purdie <rpurdie@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Add the device to the notify callback's arguments in the PWM backlight
driver. This brings the notify callback into line with the other
callbacks defined by this driver.
Signed-off-by: Ben Dooks <ben@simtec.co.uk>
Signed-off-by: Simtec Linux Team <linux@simtec.co.uk>
Signed-off-by: Richard Purdie <rpurdie@linux.intel.com>
This allows platform code to manipulate GPIOs and brightness level as
needed.
Signed-off-by: Philipp Zabel <philipp.zabel@gmail.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Patch mostly from Eric Miao, with minor edits by rmk to convert
Eric's driver to a generic PWM-based backlight driver.
Signed-off-by: eric miao <eric.miao@marvell.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
