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Reproduction of https://bugzilla.redhat.com/show_bug.cgi?id=625171 for
tracking purposes.
Description lifted from that of the Fedora bug reported by Will Woods
(2010-08-18 14:48:40 EDT):
/sys/class/backlight/nv_backlight/max_brightness is hardcoded to 1025 in
drivers/gpu/drm/nouveau/nouveau_backlight.c. But setting brightness to 1025
puts the screen brightness at something very dim.
Increasing max_brightness to 0xffff allows for (as far as I can tell) the full
range of brightness. It seems like nouveau_backlight.c needs some way to
actually determine max_brightness rather than hardcoding it.
I tried the obvious thing:
unsigned int bl = 0xffffffff;
nv_wr32(dev, NV50_PDISPLAY_SOR_BACKLIGHT, bl);
printk("nv_backlight: wrote %x, read %x\n", bl,
nv_rd32(dev, NV50_PDISPLAY_SOR_BACKLIGHT));
0xffffffff hardlocks the system; 0x80ffffff yields 0x00ffffff (which is almost
assuredly a lie).
As for guessing the actual max value - there's a noticeable difference between
44000 and 50000, but no difference that I can perceive between 50000 and 65535.
So the actual max value, wherever it's hidden, is probably somewhere between
44000 and 50000 - or the brightness scales nonlinearly as it approaches 0xffff.
** Affects: linux (Ubuntu)
Importance: Undecided
Status: New
** Tags: needs-upstream-testing
--
nouveau: MacBook Pro backlight too dim
(/sys/class/backlight/nv_backlight/max_brightness is wrong)
https://bugs.launchpad.net/bugs/625276
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