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Jani Nikula authored
Historically we've exposed the full backlight PWM duty cycle range to the userspace, in the name of "mechanism, not policy". However, it turns out there are both panels and board designs where there is a minimum duty cycle that is required for proper operation. The minimum duty cycle is available in the VBT. The backlight class sysfs interface does not make any promises to the userspace about the physical meaning of the range 0..max_brightness. Specifically there is no guarantee that 0 means off; indeed for acpi_backlight 0 usually is not off, but the minimum acceptable value. Respect the minimum backlight, and expose the range acceptable to the hardware as 0..max_brightness to the userspace via the backlight class device; 0 means the minimum acceptable enabled value. To switch off the backlight, the user must disable the encoder. As a side effect, make the backlight class device max brightness and physical PWM modulation frequency (i.e. max duty cycle) independent. This allows a follow-up patch to virtualize the max value exposed to the userspace. Signed-off-by:
Jani Nikula <jani.nikula@intel.com> Reviewed-by:
Jesse Barnes <jbarnes@virtuousgeek.org> [danvet: s/BUG_ON/WARN_ON/] Signed-off-by:
Daniel Vetter <daniel.vetter@ffwll.ch>
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