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Prevent turning the backlight completely of by setting the brightness.

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Change-Id: Idb8658f97045f6c0491223bbe8bf52914ca98402
Reviewed-on: https://review.haiku-os.org/c/haiku/+/2934
Reviewed-by: Adrien Destugues <pulkomandy@gmail.com>
This commit is contained in:
Adrien Destugues 2020-06-21 11:52:19 +02:00 committed by Adrien Destugues
parent ab1a16dea1
commit 135dff4381
1 changed files with 12 additions and 1 deletions
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13
src/add-ons/accelerants/intel_extreme/mode.cpp
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@ -537,8 +537,19 @@ intel_set_brightness(float brightness)
return B_BAD_VALUE; return B_BAD_VALUE;
uint32_t period = read32(intel_get_backlight_register(true)) >> 16; uint32_t period = read32(intel_get_backlight_register(true)) >> 16;
// The "duty cycle" is a proportion of the period (0 = backlight off,
// period = maximum brightness). The low bit must be masked out because
// it is apparently used for something else on some Atom machines (no
// reference to that in the documentation that I know of).
// Additionally we don't want it to be completely 0 here, because then
// it becomes hard to turn the display on again (at least until we get
// working ACPI keyboard shortcuts for this). So always keep the backlight
// at least a little bit on for now.
uint32_t duty = (uint32_t)(period * brightness) & 0xfffe; uint32_t duty = (uint32_t)(period * brightness) & 0xfffe;
/* Setting the low bit seems to give strange results on some Atom machines */ if (duty == 0 && period != 0)
duty = 2;
write32(intel_get_backlight_register(false), duty | (period << 16)); write32(intel_get_backlight_register(false), duty | (period << 16));
return B_OK; return B_OK;