Re: [PATCH] backlight.c: avoid unnecessarily calling backlight_update_status()

[Richard Purdie <rpurdie@rpsys.net>]

On Sun, 2008-01-06 at 15:29 +0100, Helge Deller wrote:
> Every write to the backlight control sysfs entries like (on a Sharp
> Zaurus Poodle):
> - /sys/class/backlight/locomo-bl/power
> - /sys/class/backlight/locomo-bl/brightness
> triggers a call of backlight_update_status(), even if the same
> value is written multiple times in row into those entries.
> 
> In principle this is not critical, but e.g. on the SHARP Poodle everytime
> backlight_update_status() is called, a lot of registers are reset
> and this leads to screen distortions of a ~ 0.4 seconds time frame.
> Esp. tools like some light control programs with controlling sliders 
> for the light intensity happen to set those values more often 
> which is really annoying and makes it nearly impossible to use them
> because the reaction time is really slow and you see lots of screen
> distortions.
> 
> The trivial patch below avoids this problem by comparing the 
> new value with the already set value. In case they are the same,
> it just avoids to call backlight_update_status() again.
> 
> It would be great if this patch could be applied to the fbdev git tree
> for inclusion in later linux kernels.

I've queued this in the backlight tree, thanks.

Note that ideally userspace shouldn't be making all these calls
mind ;-).

Richard


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