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

[Daniel Vetter <daniel@ffwll.ch>]

On Mon, Apr 23, 2012 at 03:15:02PM +0200, Carsten Emde wrote:
> 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)

Ok, let's try something funny. Please boot with kms enabled and try out
what the following values for CTL1 do:

# intel_reg_write 0x61250 0x80000000
# intel_reg_write 0x61250 0xa0000000
# intel_reg_write 0x61250 0x90000000
# intel_reg_write 0x61250 0xb0000000

Thanks, Daniel
-- 
Daniel Vetter
Mail: daniel@ffwll.ch
Mobile: +41 (0)79 365 57 48