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

[Carsten Emde <C.Emde@osadl.org>]

On 04/23/2012 02:36 PM, Daniel Vetter wrote:
> On Mon, Apr 23, 2012 at 02:32:57PM +0200, Daniel Vetter wrote:
>> On Mon, Apr 23, 2012 at 01:54:23PM +0200, Carsten Emde wrote:
>>> On 04/23/2012 11:32 AM, Daniel Vetter wrote:
>>>> There's a bit in the docs for gen4 only that says whether the
>>>> backlight control is inverted. And both the quirk we have and
>>>> all bugs only concern i965gm and gm45 (and mostly Acer) afaics.
>>>>
>>>> So lets drop the quirk and use the bit instead.
>>>>
>>>> Also clean up the BLC register definitions a bit by correctly
>>>> grouping the CTL and CTL2 definitions together.
>>>> [..]
>>>> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
>>>> index 4c844c6..5d215f0 100644
>>>> --- a/drivers/gpu/drm/i915/intel_display.c
>>>> +++ b/drivers/gpu/drm/i915/intel_display.c
>>>> @@ -6482,9 +6482,6 @@ static struct intel_quirk intel_quirks[] = {
>>>>
>>>>   	/* Sony Vaio Y cannot use SSC on LVDS */
>>>>   	{ 0x0046, 0x104d, 0x9076, quirk_ssc_force_disable },
>>>> -
>>>> -	/* Acer Aspire 5734Z must invert backlight brightness */
>>>> -	{ 0x2a42, 0x1025, 0x0459, quirk_invert_brightness },
>>> Made a first test with these lines removed and the new mechanism
>>> added.  Unfortunately, the screen is now dark again. Works after
>>> re-adding the quirk.
>>>
>>>> +	/* gen4 has a polarity bit */
>>>> +	if (IS_GEN4(dev) && (I915_READ(BLC_PWM_CTL2) & BLM_POLARITY_I965))
>>>> +			return intel_panel_get_max_backlight(dev) - val;
>>>> +
>>> Apparently, these conditions are not met on the Acer Aspire 5734Z.
>>> Will add some debug output and evaluate further. For the time being,
>>> please leave the quirk in place.
>>
>> Hm, I've tried this and when I set this bit, panel brightness is inverted
>> on my gm45. Can you install intel-gpu-tools and read out the 2 backlight
>> control registers with
>>
>> # intel_reg_read 0x61254
>> # intel_reg_read 0x61250
>
> I've forgotten to add: Also please grab these register values when booting
> with nomodeset, so that we can compare the values the bios sets with
> whatever i915 sets.

Without nomodeset:
# intel_reg_read 0x61254
0x61254 : 0xB4A0B4A
# intel_reg_read 0x61250
0x61250 : 0xE0000000

With nomodeset:
# intel_reg_read 0x61254
0x61254 : 0xB4A0B4A
# intel_reg_read 0x61250
0x61250 : 0xE0000000

Thus, (I915_READ(BLC_PWM_CTL2) & BLM_POLARITY_I965) is never set. But 
bit 29 would work, so we could add another conditional such as:
#define BLM_POLARITY_PCH_I965 (1 << 29) /* PCH only */
if (PCH)
   try (I915_READ(BLC_PWM_CTL2) & BLM_POLARITY_PCH_I965)

	-Carsten.