From cee90ae0fce6d6aee8d78969b60c952c8890abd6 Mon Sep 17 00:00:00 2001 From: Francis Rowe Date: Fri, 11 Jul 2014 08:53:00 +0000 Subject: Libreboot release 6 beta 1. --- docs/i945_backlight.html | 118 +++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 118 insertions(+) create mode 100644 docs/i945_backlight.html (limited to 'docs/i945_backlight.html') diff --git a/docs/i945_backlight.html b/docs/i945_backlight.html new file mode 100644 index 00000000..1ce01373 --- /dev/null +++ b/docs/i945_backlight.html @@ -0,0 +1,118 @@ + + + + + i945 backlight in libreboot + + + + + + + + + + + +

i945 backlight controls on X60/T60

+ +

+ back to index +

+ +

X60 native graphics initialization (backlight controls)
T60 native graphics initialization (backlight controls)

+ +

X60 native graphics initialization (with backlight controls)

+ The fix below was done on 5320/6 (review.coreboot.org) under src/mainboard/lenovo/x60/devicetree.cb +

+ Works on the ThinkPad X60, X60s and X60 Tablet. This change is also included by default in libreboot 6th release. +

+ Add backlight controls: in src/mainboard/lenovo/x60/devicetree.cb, change gpu_backlight to 0x879F879E +

+ That's all! This was also backported into libreboot 5th release (line 1233 in src/mainboard/lenovo/x60/i915io.c). GNUtoo (Denis Carikli) + told me about the register BLC_PWM_CTL and that you could set it to control backlight. I read that address using devmem2 while running the VBIOS:
+ # devmem2 0xe4361254 w +

+ When doing this, it gave back that value. The same trick was used to get backlight controls for T60 (see #t60_native_notes). +

+ +

Further notes (as of 6th libreboot release, initial revision)

+ Reading 0xe4361254 (address) in Lenovo BIOS always yields FFFFFFFF, even when writing to it (and writing to it doesn't affect brightness controls). + 'mtjm' on IRC found that the buttons (Fn keys) control /sys/class/backlight/acpi_video0 which has no affect on 61254 (BLC_PWM_CTL). He says + intel_backlight has different values and uses the register. devmem2 works, needs checking lspci -vv for where the memory is mapped, + which is different than on coreboot; mtjm found that it was 0xec061254 on his machine (X60 Tablet), and the register value is different too. + This is relevant, because we still don't know how backlight controls are actually handled. We got it working by accident. We need to know more.. +

+ Intel-gpu-tools may prove useful for further debugging: http://cgit.freedesktop.org/xorg/app/intel-gpu-tools/ +

+ mtjm says 0xe4300000 is an MMIO region of the gpu (lspci -vv shows it), 0x61254 (BLC_PWM_CTL) is a documented register. Searching the kernel driver for backlight + shows that in intel_panel.c this register is used (there is an XXX comment about finding the right value, where recent kernels get it from. +

+ What we want to do is calculate a good value, instead of setting it in devicetree.cb. mtjm says about backlight physics: + it has a light source , uses pulse width modulation (PWM) to turn it on/off, dimming is done by spending less time on. + Note: this may not be correct; he says his understanding is based on how the Lenote yeeloong works. +

+ mtjm goes on to say, that the register specifies the frequency used for PWM in its depending on the GPU core frequency, so it + might be possible to calculate it without hardcoded laptop-specific values. Therefore, I am supposed to find out the 'display core frequency' + (mtjm says there might be a register for it; also, it might be in 5320 or the replay code) and the PWM modulation frequency. + https://en.wikipedia.org/wiki/Backlight#Flicker_due_to_backlight_dimming +

+ phcoder (Vladimir Serbinenko) who is author of 5320 (review.coreboot.org) talks about 'duty cycle limit' and 'flickering frequency'. +

+ +

T60 native graphics initialization (with backlight controls)

+ The fix below was done on an earlier version of 5345 (review.coreboot.org) cherry-picked on top of 5320 checkout, but also works on the current version. +

+ This change is also included by default in libreboot 6th release. +

+ Add backlight controls: in src/mainboard/lenovo/t60/devicetree.cb, change gpu_backlight to 0x58BF58BE +

+ +

+ + + + -- cgit v1.2.3-70-g09d2

Contents

X60 native graphics initialization (with backlight controls)

Further notes (as of 6th libreboot release, initial revision)

T60 native graphics initialization (with backlight controls)