|Subject:||Re: [Libreboot] X60 tablet: screen whine after 1400x1050 screen swap|
|Date:||Mon, 6 Apr 2015 02:07:52 -0400|
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BLC_PWM_CTL is in src/mainboard/lenovo/x60/devicetree.cb, see
gpu_brightness or gpu_backlight or something like that. You can change
the value there.
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On 06/04/15 05:54, Charles Devereaux wrote:
> On my X60 tablet, after a screen swap for a 1400x1050 screen, I
> started noticing a whine. The noise is proportional to the
> reduction of the backlight and doesn't happen at full brightness. I
> never noticed it before.
> It happens regardless of how I change the backlight (fn+home/end,
> xbacklight, custom script reading and writing to
> /sys/class/backlight/intel_backlight/brightness) so I suspect a
> coreboot issue.
> I am currently using an old libreboot based on head
> 8ffc085e1affaabbe3dca8ac6a89346b71dfc02e with #5345, #7050, #7051,
> but not #6731 and #7049 (since they were dropped and I do not need
> acpi backlight) that works just fine, so I am a bit reluctant to
> change it.
> Apparently #6731 and #7049 had the same problem: "some lower
> brightness levels make the high-pitched noise", which was fixed cf
> After looking at the code, I see a note explaining how: "Francis
> tested that like my noise issue it doesn't occur with a lower PWM
> If we compute the frequency as (0x61 << 8) + (0x61 << 6) + 1 (the 1
> is to allow legacy backlight brightness which the VGA ROM allows
> and I don't know if it should be enabled) and duty cycle as (x <<
> 8) + (x << 6) for x in 0xf, ..., 0x61, then both our issues are
> I don't know if the resulting value (0x79417940) gives low enough
> frequency to cause flickering for other users: "
> I do not fully understand where or how the PWM frequency is set in
> src/northbridge/intel/i945/gma.c. I never see that 0x79417940
> either. the only thing I see in
> write32(pmmio + BLC_PWM_CTL, 0x6100610);
> In the source of my libreboot, it is still:
> write32(pmmio + BLC_PWM_CTL, conf->gpu_backlight);
> With src/mainboard/lenovo/x60/devicetree.cb setting it with:
> register "gpu_backlight" = "0x879F879E"
> Should it get changed to:
> write32(pmmio + BLC_PWM_CTL, 0x79417940) The other thing I noticed
> were kernel warnings on wakeup from suspend2ram: [54557.710112]
> [drm:intel_pipe_config_compare] *ERROR* mismatch in
> gmch_pfit.pgm_ratios (expected 24183152, found 24117616)
> [54557.710114] ------------[ cut here ]------------ [54557.710121]
> WARNING: CPU: 1 PID: 1432 at
> check_crtc_state+0x759/0xe31() [54557.710122] pipe state doesn't
> It may be related. Which coreboot head/patches is libreboot on the
> X60 presently using?
> Thanks Charles
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