Re: [PATCH 1/2] drm/i915: clear up backlight inversion confusion on gen4

Carsten Emde
2012-04-23T15:13:16Z

On 04/23/2012 04:22 PM, Daniel Vetter wrote:
> On Mon, Apr 23, 2012 at 04:00:23PM +0200, Carsten Emde wrote:
>> # intel_reg_write 0x61250 0x80000000
>> Value before: 0xE0000000
>> Value after: 0x80000000
>> # intel_reg_read 0x61254
>> 0x61254 : 0xB4A0B4A
>>
>> # intel_reg_write 0x61250 0xa0000000
>> Value before: 0x80000000
>> Value after: 0xA0000000
>> # intel_reg_read 0x61254
>> 0x61254 : 0xB4A0B4A
>>
>> # intel_reg_write 0x61250 0x90000000
>> Value before: 0xA0000000
>> Value after: 0x90000000
>> # intel_reg_read 0x61254
>> 0x61254 : 0xB4A0B4A
>>
>> # intel_reg_write 0x61250 0xb0000000
>> Value before: 0x90000000
>> Value after: 0xB0000000
>> # intel_reg_read 0x61254
>> 0x61254 : 0xB4A0B4A
>>
>> Not much.
>
> The idea was to boot with kms and see whether any of these values would
> restore the backlight. Writing to CTL1 should change anything in CTL2.
Ah, sorry, ok. Removed the quirk again and tested the various settings:

-> Initial screen: dark

# intel_reg_write 0x61250 0x80000000
Value before: 0xE0000000
Value after: 0x80000000
-> Still dark

# intel_reg_write 0x61250 0xa0000000
Value before: 0x80000000
Value after: 0xA0000000
-> Still dark

# intel_reg_write 0x61250 0x90000000
Value before: 0xA0000000
Value after: 0x90000000
-> BACKLIGHT ON!

# intel_reg_write 0x61250 0xb0000000
Value before: 0x90000000
Value after: 0xB0000000
-> Still ON.

-Carsten.