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	<title>LCD compatibility on GM45 laptops</title>
</head>

<body>

	<div class="section">
		<h1 id="pagetop">LCD compatibility on GM45 laptops</h1>
			
			<p>
				On the T400 and T500 (maybe others), some of the higher resolution panels
				(e.g. 1440x900, 1680x1050, 1920x1200) fail in libreboot.
			</p>

			<p>
				It is currently unknown, whether there exist any compatibility issues on the ThinkPad R500.
			</p>

			<p>
				<b>All X200/X200S/X200T LCD panels are believed to be compatible.</b>
			</p>
			
			<p>
				<a href="index.html">Back to previous index</a>.
			</p>
	</div>

	<div class="section">
		<h1>The problem</h1>
			<p>
				In some cases, backlight turns on during boot, sometimes not. In all cases,
				no display is shown in GRUB, nor in GNU/Linux.
			</p>
		<h1>
			Current workaround:
		</h1>
			<p>
				T500/R400 are clones of the T400. See <b>coreboot/src/mainboard/lenovo/t400/devicetree.cb</b> in libreboot,
				and note that <b>register "gfx.lvds_dual_channel" = "0"</b> - in other words, single channel LVDS mode is
				enforced. This works on the lower resolution panels (1280x800), but not on the higher ones.
			</p>
			<p>
				For the high-res panels, re-compiling with <b>register "gfx.lvds_dual_channel" = "1"</b> partially solves
				the problem for those displays; there is still no display in GRUB, but once the kernel takes over, there
				is a display.
			</p>
			<p>
				Linux (kernel) has its own init code (including EDID parsing). The current suspicion is that coreboot's
				own initialization code has buggy EDID parsing in some way, such that the proper settings for the panel
				are not used, leading to the failure. The actual graphics initialization does work.
			</p>

			<p>
				The i915 module in the Linux kernel also provides an option to set the LVDS link configuration.
				lvds_channel_mode:Specify LVDS channel mode (0=probe BIOS [default], 1=single-channel, 2=dual-channel) (int)
				- from /sbin/modinfo i915
			</p>
	</div>

	<div class="section">
		<h1>Differences in dmesg (kernel parameter added: )</h1>
			<p>
				<a href="https://01.org/linuxgraphics/documentation/how-report-bugs">https://01.org/linuxgraphics/documentation/how-report-bugs</a>
			</p>
			<p>
				These panels all work in the original firmware, so the idea is to see what differences there are in how coreboot handles them.
			</p>
			<p>
				<a href="http://www.coreboot.org/pipermail/coreboot/attachments/20150712/d2e214bb/attachment-0002.txt">dmesg with coreboot-libre</a> (coreboot) - 
				See: <i>[drm:intel_lvds_init] detected single-link lvds configuration</i>
			</p>
			<p>
				<a href="http://www.coreboot.org/pipermail/coreboot/attachments/20150712/d2e214bb/attachment-0003.txt">dmesg with lenovobios</a> (lenovobios) - 
				For the same line, it says dual-channel lvds configuration.
			</p>
	</div>
	
	<div class="section">

		<h2 id="edid">EDID</h2>

		<p>
			One T500 had a screen (1920x1200) that is currently incompatible. Working to fix it. EDID:
		</p>
<pre>
user@user-ThinkPad-T500:~/Desktop$ sudo i2cdump -y 2 0x50
No size specified (using byte-data access)
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f    0123456789abcdef
00: XX ff ff ff ff ff ff 00 30 ae 55 40 00 00 00 00    X.......0?U@....
10: 00 11 01 03 80 21 15 78 ea ba 70 98 59 52 8c 28    .????!?x??p?YR?(
20: 25 50 54 00 00 00 01 01 01 01 01 01 01 01 01 01    %PT...??????????
30: 01 01 01 01 01 01 e7 3a 80 8c 70 b0 14 40 1e 50    ???????:??p??@?P
40: 24 00 4b cf 10 00 00 19 16 31 80 8c 70 b0 14 40    $.K??..??1??p??@
50: 1e 50 24 00 4b cf 10 00 00 19 00 00 00 0f 00 d1    ?P$.K??..?...?.?
60: 0a 32 d1 0a 28 11 01 00 32 0c 00 00 00 00 00 fe    ?2??(??.2?.....?
70: 00 4c 50 31 35 34 57 55 31 2d 54 4c 42 31 00 9a    .LP154WU1-TLB1.?
80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................
90: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................
a0: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................
b0: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................
c0: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................
d0: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................
e0: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................
f0: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................
</pre>
		<p>
			What happens: backlight turns on at boot, then turns off. At no point is there
			a working visual display.
		</p>

		<p>
			Another incompatible screen (EDID) 1680 x 1050 with the same issue:
		</p>
<pre>
EDID:
00 ff ff ff ff ff ff 00 30 ae 53 40 00 00 00 00 
00 11 01 03 80 21 15 78 ea cd 75 91 55 4f 8b 26 
21 50 54 00 00 00 01 01 01 01 01 01 01 01 01 01 
01 01 01 01 01 01 a8 2f 90 e0 60 1a 10 40 20 40 
13 00 4b cf 10 00 00 19 b7 27 90 e0 60 1a 10 40 
20 40 13 00 4b cf 10 00 00 19 00 00 00 0f 00 b3 
0a 32 b3 0a 28 14 01 00 4c a3 50 33 00 00 00 fe 
00 4c 54 4e 31 35 34 50 33 2d 4c 30 32 0a 00 7e 
Extracted contents:
header:          00 ff ff ff ff ff ff 00
serial number:   30 ae 53 40 00 00 00 00 00 11
version:         01 03
basic params:    80 21 15 78 ea
chroma info:     cd 75 91 55 4f 8b 26 21 50 54
established:     00 00 00
standard:        01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01
descriptor 1:    a8 2f 90 e0 60 1a 10 40 20 40 13 00 4b cf 10 00 00 19
descriptor 2:    b7 27 90 e0 60 1a 10 40 20 40 13 00 4b cf 10 00 00 19
descriptor 3:    00 00 00 0f 00 b3 0a 32 b3 0a 28 14 01 00 4c a3 50 33
descriptor 4:    00 00 00 fe 00 4c 54 4e 31 35 34 50 33 2d 4c 30 32 0a
extensions:      00
checksum:        7e

Manufacturer: LEN Model 4053 Serial Number 0
Made week 0 of 2007
EDID version: 1.3
Digital display
Maximum image size: 33 cm x 21 cm
Gamma: 220%
Check DPMS levels
DPMS levels: Standby Suspend Off
Supported color formats: RGB 4:4:4, YCrCb 4:2:2
First detailed timing is preferred timing
Established timings supported:
Standard timings supported:
Detailed timings
Hex of detail: a82f90e0601a1040204013004bcf10000019
Did detailed timing
Detailed mode (IN HEX): Clock 122000 KHz, 14b mm x cf mm
               0690 06b0 06f0 0770 hborder 0
               041a 041b 041e 042a vborder 0
               -hsync -vsync 
Hex of detail: b72790e0601a1040204013004bcf10000019
Detailed mode (IN HEX): Clock 122000 KHz, 14b mm x cf mm
               0690 06b0 06f0 0770 hborder 0
               041a 041b 041e 042a vborder 0
               -hsync -vsync 
Hex of detail: 0000000f00b30a32b30a281401004ca35033
Manufacturer-specified data, tag 15
Hex of detail: 000000fe004c544e31353450332d4c30320a
ASCII string: LTN154P3-L02
Checksum
Checksum: 0x7e (valid)
WARNING: EDID block does NOT fully conform to EDID 1.3.
        Missing name descriptor
        Missing monitor ranges
bringing up panel at resolution 1680 x 1050
Borders 0 x 0
Blank 224 x 16
Sync 64 x 3
Front porch 32 x 1
Spread spectrum clock
Single channel
Polarities 1, 1
Data M1=2132104, N1=8388608
Link frequency 270000 kHz
Link M1=236900, N1=524288
Pixel N=9, M1=24, M2=8, P1=1
Pixel clock 243809 kHz
waiting for panel powerup
panel powered up
</pre>

		<p>
			Another incompatible (T400) screen:
		</p>
<pre>
No size specified (using byte-data access)
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f    0123456789abcdef
00: XX ff ff ff ff ff ff 00 30 ae 33 40 00 00 00 00    X.......0?3@....
10: 00 0f 01 03 80 1e 13 78 ea cd 75 91 55 4f 8b 26    .??????x??u?UO?&amp;
20: 21 50 54 00 00 00 01 01 01 01 01 01 01 01 01 01    !PT...??????????
30: 01 01 01 01 01 01 b0 27 a0 60 51 84 2d 30 30 20    ???????'?`Q?-00 
40: 36 00 2f be 10 00 00 19 d5 1f a0 40 51 84 1a 30    6./??..????@Q??0
50: 30 20 36 00 2f be 10 00 00 19 00 00 00 0f 00 90    0 6./??..?...?.?
60: 0a 32 90 0a 28 14 01 00 4c a3 42 44 00 00 00 fe    ?2??(??.L?BD...?
70: 00 4c 54 4e 31 34 31 57 44 2d 4c 30 35 0a 00 32    .LTN141WD-L05?.2
80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................
90: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................
a0: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................
b0: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................
c0: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................
d0: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................
e0: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................
f0: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................

</pre>

		<p>
			For comparison, here is a working display (T400 screen, but was
			connected to a T500. Some T500 displays also work, but no EDID
			available on this page yet):
		</p>
<pre>
EDID:
00 ff ff ff ff ff ff 00 30 ae 31 40 00 00 00 00 
00 12 01 03 80 1e 13 78 ea b3 85 95 58 53 8a 28 
25 50 54 00 00 00 01 01 01 01 01 01 01 01 01 01 
01 01 01 01 01 01 26 1b 00 7d 50 20 16 30 30 20 
36 00 30 be 10 00 00 18 8b 16 00 7d 50 20 16 30 
30 20 36 00 30 be 10 00 00 18 00 00 00 0f 00 81 
0a 32 81 0a 28 14 01 00 30 e4 28 01 00 00 00 fe 
00 4c 50 31 34 31 57 58 33 2d 54 4c 52 31 00 d8 
Extracted contents:
header:          00 ff ff ff ff ff ff 00
serial number:   30 ae 31 40 00 00 00 00 00 12
version:         01 03
basic params:    80 1e 13 78 ea
chroma info:     b3 85 95 58 53 8a 28 25 50 54
established:     00 00 00
standard:        01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01
descriptor 1:    26 1b 00 7d 50 20 16 30 30 20 36 00 30 be 10 00 00 18
descriptor 2:    8b 16 00 7d 50 20 16 30 30 20 36 00 30 be 10 00 00 18
descriptor 3:    00 00 00 0f 00 81 0a 32 81 0a 28 14 01 00 30 e4 28 01
descriptor 4:    00 00 00 fe 00 4c 50 31 34 31 57 58 33 2d 54 4c 52 31
extensions:      00
checksum:        d8

Manufacturer: LEN Model 4031 Serial Number 0
Made week 0 of 2008
EDID version: 1.3
Digital display
Maximum image size: 30 cm x 19 cm
Gamma: 220%
Check DPMS levels
DPMS levels: Standby Suspend Off
Supported color formats: RGB 4:4:4, YCrCb 4:2:2
First detailed timing is preferred timing
Established timings supported:
Standard timings supported:
Detailed timings
Hex of detail: 261b007d502016303020360030be10000018
Did detailed timing
Detailed mode (IN HEX): Clock 69500 KHz, 130 mm x be mm
               0500 0530 0550 057d hborder 0
               0320 0323 0329 0336 vborder 0
               -hsync -vsync 
Hex of detail: 8b16007d502016303020360030be10000018
Detailed mode (IN HEX): Clock 69500 KHz, 130 mm x be mm
               0500 0530 0550 057d hborder 0
               0320 0323 0329 0336 vborder 0
               -hsync -vsync 
Hex of detail: 0000000f00810a32810a2814010030e42801
Manufacturer-specified data, tag 15
Hex of detail: 000000fe004c503134315758332d544c5231
ASCII string: LP141WX3-TLR1
Checksum
Checksum: 0xd8 (valid)
WARNING: EDID block does NOT fully conform to EDID 1.3.
        Missing name descriptor
        Missing monitor ranges
bringing up panel at resolution 1280 x 800
Borders 0 x 0
Blank 125 x 22
Sync 32 x 6
Front porch 48 x 3
Spread spectrum clock
Single channel
Polarities 1, 1
Data M1=1214600, N1=8388608
Link frequency 270000 kHz
Link M1=134955, N1=524288
Pixel N=10, M1=14, M2=11, P1=1
Pixel clock 138857 kHz
waiting for panel powerup
panel powered up
</pre>

		<p>
			Another compatible T400 screen:
		</p>
<pre>
trisquel@trisquel:~$ sudo i2cdump -y 2 0x50
No size specified (using byte-data access)
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f    0123456789abcdef
00: 00 ff ff ff ff ff ff 00 30 ae 31 40 00 00 00 00    ........0?1@....
10: 00 12 01 03 80 1e 13 78 ea b3 85 95 58 53 8a 28    .??????x????XS?(
20: 25 50 54 00 00 00 01 01 01 01 01 01 01 01 01 01    %PT...??????????
30: 01 01 01 01 01 01 26 1b 00 7d 50 20 16 30 30 20    ??????&?.}P ?00 
40: 36 00 30 be 10 00 00 18 8b 16 00 7d 50 20 16 30    6.0??..???.}P ?0
50: 30 20 36 00 30 be 10 00 00 18 00 00 00 0f 00 81    0 6.0??..?...?.?
60: 0a 32 81 0a 28 14 01 00 30 e4 28 01 00 00 00 fe    ?2??(??.0?(?...?
70: 00 4c 50 31 34 31 57 58 33 2d 54 4c 52 31 00 d8    .LP141WX3-TLR1.?
80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................
90: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................
a0: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................
b0: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................
c0: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................
d0: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................
e0: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................
f0: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff    ................
</pre>

	</div>

	<div class="section">

		<p>
			Copyright &copy;  2015 Francis Rowe &lt;info@gluglug.org.uk&gt;<br/>
			Permission is granted to copy, distribute and/or modify this document
			under the terms of the GNU Free Documentation License, Version 1.3
			or any later version published by the Free Software Foundation;
			with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.
			A copy of the license can be found at <a href="../gfdl-1.3.txt">../gfdl-1.3.txt</a>
		</p>

		<p>
			Updated versions of the license (when available) can be found at
			<a href="https://www.gnu.org/licenses/licenses.html">https://www.gnu.org/licenses/licenses.html</a>
		</p>

		<p>
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