On 24/02/17 08:43, Jani Nikula wrote:
>> - "Some PWM based backlight allow adjusting the PWM modulation
>> frequency." you don't need a motivation for *why* I would want to
>> change the mod freq on the fly, actually in my experience you
>> shouldn't since this can lead to flickery backlights.
>
> The modulation frequency is usually an OEM design choice. The higher
> the
> frequency, less flicker, but also fewer user distinguishable levels of
> backlight (signal rise/fall times come into play). Occasionally there
> have been requests to be able to adjust the frequency. We can of course
> decide that's an implementation detail and not let userspace change it.
In principle the backlight max level could also change during monitor
hotplug; recent versions DDC/CI include a backlight properties. We have
no driver for this right now but conversation is starting (and proper
backlight support in DRM connectors will probably help it happen faster).
I'm afraid I have no idea if this is "real" or now. Right now I have no
clue how many monitors implement it. For regular desktop monitors which
mirror old school brightness/contrast in their UI then 0 wouldn't
surprise me much ;-)
Daniel.
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