diff options
Diffstat (limited to 'docs/i945_backlight.html')
| -rw-r--r-- | docs/i945_backlight.html | 118 |
1 files changed, 118 insertions, 0 deletions
diff --git a/docs/i945_backlight.html b/docs/i945_backlight.html new file mode 100644 index 0000000..1ce0137 --- /dev/null +++ b/docs/i945_backlight.html @@ -0,0 +1,118 @@ +<!DOCTYPE html> +<html lang="en"> +<head> + <meta charset="utf-8"> + <title>i945 backlight in libreboot</title> + + <style type="text/css"> + body { + font-family: sans-serif; + font-size: 1em; + background: #fff; + color: #000; + } + + </style> + + <meta name="viewport" content="width=device-width, initial-scale=1.0"> + <meta name="author" content="glugman"> + <meta name="description" content="tutorials for libreboot, the reboot library."> + <meta name="robots" content="all"> +</head> + +<body> + + <header> + <h1 id="pagetop">i945 backlight controls on X60/T60</h1> + </header> + + <p> + <a href="index.html">back to index</a> + </p> + +<hr/> + + <h2>Contents</h2> + <ul> + <li><a href="#x60_native_notes">X60 native graphics initialization (backlight controls)</a></li> + <li><a href="#t60_native_notes">T60 native graphics initialization (backlight controls)</a></li> + </ul> + +<hr/> + + <h1 id="x60_native_notes">X60 native graphics initialization (with backlight controls)</h1> + <p> + <b>The fix below was done on 5320/6 (review.coreboot.org) under src/mainboard/lenovo/x60/devicetree.cb</b> + </p> + <p> + Works on the ThinkPad X60, X60s and X60 Tablet. This change is also included by default in libreboot 6th release. + </p> + <p> + <b>Add backlight controls:</b> in <i>src/mainboard/lenovo/x60/devicetree.cb</i>, change <b>gpu_backlight</b> to <b>0x879F879E</b> + </p> + <p> + That's all! <b>This was also backported into libreboot 5th release (line 1233 in src/mainboard/lenovo/x60/i915io.c)</b>. GNUtoo (Denis Carikli) + told me about the register <b>BLC_PWM_CTL</b> and that you could set it to control backlight. I read that address using devmem2 while running the VBIOS:<br/> + <b># devmem2 0xe4361254 w</b> + </p> + <p> + When doing this, it gave back that value. The same trick was used to get backlight controls for T60 (see <a href="#t60_native_notes">#t60_native_notes</a>). + </p> + + <h2>Further notes (as of 6th libreboot release, initial revision)</h2> + <p> + Reading <b>0xe4361254</b> (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 <b>lspci -vv</b> 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. + <b>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.</b>. + </p> + <p> + Intel-gpu-tools may prove useful for further debugging: <a href="http://cgit.freedesktop.org/xorg/app/intel-gpu-tools/">http://cgit.freedesktop.org/xorg/app/intel-gpu-tools/</a> + </p> + <p> + 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. + </p> + <p> + 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. + <b>Note: this may not be correct; he says his understanding is based on how the Lenote yeeloong works</b>. + </p> + <p> + 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 + </p> + <p> + phcoder (Vladimir Serbinenko) who is author of 5320 (review.coreboot.org) talks about 'duty cycle limit' and 'flickering frequency'. + </p> + + <p><a href="#pagetop">Back to top of page</a></p> + +<hr/> + + <h1 id="t60_native_notes">T60 native graphics initialization (with backlight controls)</h1> + <p> + <b>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.</b> + </p> + <p> + This change is also included by default in libreboot 6th release. + </p> + <p> + <b>Add backlight controls:</b> in <i>src/mainboard/lenovo/t60/devicetree.cb</i>, change <b>gpu_backlight</b> to <b>0x58BF58BE</b> + </p> + + <p><a href="#pagetop">Back to top of page</a></p> + +<hr/> + + <p> + Copyright © 2014 Francis Rowe, All Rights Reserved.<br/> + See <a href="license.html">license.html</a> for license conditions. + </p> + +</body> +</html> + |