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[Dave Walker <davewalker@xxxxxxxxxx>]

Public bug reported:

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: Confirmed

** Affects: linux (Fedora)
     Importance: Unknown
         Status: Unknown

** Changed in: linux (Ubuntu)
       Status: New => Confirmed

** Bug watch added: Red Hat Bugzilla #625171
   https://bugzilla.redhat.com/show_bug.cgi?id=625171

** Also affects: linux (Fedora) via
   https://bugzilla.redhat.com/show_bug.cgi?id=625171
   Importance: Unknown
       Status: Unknown

** Description changed:

  Reproduction of https://bugzilla.redhat.com/show_bug.cgi?id=625171 for
  tracking purposes.
  
- Description lifted from that of the RedHat bug reported by Will Woods (2010-08-18 14:48:40 EDT):
+ 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));
+   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). 
+ 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.

-- 
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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