libreboot tutorials
Author: glugman
Description: tutorials for libreboot, the reboot library.

# Development notes (old/obsolete notes)

For current notes, see index.html.

These are old (obsolete) notes that mare kept because they might become useful again in the future.

# Table of contents

- X60 native graphics initialization (backlight controls)
- T60 native graphics initialization (backlight controls)
- i945: 3D fix (based on 5927) for kernel 3.12+ on 5320
- i945/x60: coreboot 5927 testing (3D fix for kernel 3.12+ on replay code)

# X60 native graphics initialization (with backlight controls)

This is now obsolete. A better way was found (included in libreboot): http://review.coreboot.org/#/c/6731/

Also check #5320_kernel312fix (to fix 3D on kernel 3.12/higher)

The fix below was done on 5320/6 (from review.coreboot.org) but should work just fine on later versions of 5320.

Native gpu init + backlight controls! (Fn keys). Also confirmed on X60 Tablet (1024x768) and X60 Tablet (1400x1050)

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

That's all! This has also been 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

The change is also included in libreboot 6.

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

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'.

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# T60 native graphics initialization (with backlight controls)

This is now obsolete. A better way was found (included in libreboot): http://review.coreboot.org/#/c/6731/

Also check #5320_kernel312fix (to fix 3D on kernel 3.12/higher)

The fix below was done on an earlier version of 5345 changeset (review.coreboot.org), but should work on the current version. it is included in libreboot 6

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

Hold on! Check ../misc/index.html#get_edid_panelname to know what LCD panel you have. This is important for the next step!

## Supported panels

../hcl/index.html#supported_t60_list.

See index.html#lcd_i945_incompatibility.

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# i945: 3D fix (based on 5927) for kernel 3.12+ on 5320

This is now obsolete. Merged in coreboot: http://review.coreboot.org/#/c/5927/

This needs to be rewritten (or better organized, or deleted?). This is also now included in libreboot 6 (using the proper way, not the 7c0000 method which was a hack)

This was done on 5320/6 so far. The fix below is for 5320/6 which is now obsolete. This needs to be re-done for the latest version of 5320. The fix below is (in practise) only for reference, therefore.

See #x60_cb5927_testing for the original (and current) fix, for the replay code. Now we want to implement that on top of http://review.coreboot.org/#/c/5320 which is the current code for native graphics initialization on i945.

src/northbridge/intel/i945/gma.c (using the 7c0000 hack) on 5320: 5320_7c0000_gma.c (rename it to gma.c, replacing the current one).

The above is a hack (as is the original). A better (more correct) method is implemented in later versions of 5927, so that should also be adapted for 5320. For now, you can use the above fix.

The correct way to do it is to set gtt address to (end of stolen memory - gtt size), which is what later versions of 5927 do (successfully).

Here is some debugging output using intel_gpu_tools v1.2-1 (from trisquel repositories) using tool "intel_gtt":

- Trisquel 6. kernel 3.14.4:
  - with libreboot 5th release (using the 7c0000 gtt hack from 5927/3): http://paste.debian.net/104306
  - with coreboot+vgarom: http://paste.debian.net/104309
- Trisquel 6. kernel 3.2.0-60 (from Trisquel repositories):
  - with coreboot (no vbios or native init): http://paste.debian.net/104341

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# i945/X60: Coreboot 5927 testing (3D fix for kernel 3.12+ on replay code)

This is now obsolete. Merged in coreboot: http://review.coreboot.org/#/c/5927/

The latest version as-is (5927/11) has not been tested by me yet. Always boot with 'drm.debug=0x06' kernel parameter when testing this.

This is the fix for 3D on kernel 3.12 and higher on i945 (ThinkPad X60 in this case). This is for the replay code. Libreboot 5th release has a version of this backported already (based on 5927/3 using the '7c0000' hack).

The replay code is obsolete (see 5320 changeset on review.coreboot.org for better version which supports more machines/screens, and then 5345 for T60). Information here for reference since that is where the fix was first applied.

Read the information on http://review.coreboot.org/#/c/5927/.

For historical purposes, here is a collection of IRC logs that once existed on this page, related to the issue: kernel312_irc.

PGETBL_CTL differs between VBIOS (-) and native graphics init (+).
- PGETBL_CTL: 0x3ffc0001
+ PGETBL_CTL: 0x3f800001

GTT (graphics translation table) size is PGETBL_save, max 256 KiB. BSM (Base of Stolen Memory) is given by the bios.

- 5927/7: 5927_7.tar.gz (GRUB graphics are correct now, and 3D still works)
- 5927/6: 5927_6.tar.gz (GRUB graphics still corrupt, 3D/everything still works after GRUB)
- 5927/5: 5927_5.tar.gz (GRUB graphics corrupt, 3D/everything still works after GRUB)
- 5927/3: 5927_3.tar.gz (3D still works! kernel 3.14.4) - the '7c0000' hack
- 5927/2: 5927_2.tar.gz (3D works! kernel 3.14.4) - the '7c0000' hack
- 5927/1 (didn't fix the 3D issue):
  - cbmem -c
  - /sys/class/drm/card0/error
  - .config

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Copyright © 2014, 2015 Francis Rowe <info@gluglug.org.uk>
This document is released under the Creative Commons Attribution-ShareAlike 4.0 International Public License and all future versions. A copy of the license can be found at ../license.txt.

This document is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See ../license.txt for more information.