New patch to review for coreboot: WIP Documentation/backlight-pwm: Gather backlight PWM infos

[Nico Huber]

Nico Huber ([e-mail]) just uploaded a new patch set to gerrit, which you can find at https://review.coreboot.org/18250

-gerrit

commit 96e2f885c196913cd1aebe43f6fc9c0f0b31df78
Author: Nico Huber 
Date:   Fri Jan 27 15:55:28 2017 +0100

WIP Documentation/backlight-pwm: Gather backlight PWM infos

Change-Id: I3a3456cee8ed053db13b4b9d2d3f5a8fc04bb7ff
    Signed-off-by: Nico Huber 
---
 Documentation/backlight-pwm.md | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/Documentation/backlight-pwm.md b/Documentation/backlight-pwm.md
new file mode 100644
index 0000000..970646f
--- /dev/null
+++ b/Documentation/backlight-pwm.md
@@ -0,0 +1,25 @@
+# PWM frequencies for display backlights
+
+## Values found in use by vendors
+
+* `Lenovo ThinkPad X60`: 0x879e/180Hz (@200MHz CDClk)
+
+* `Lenovo ThinkPad X200s`: 0x0cf8/753Hz (@320MHz CDClk)
+  LED backlight, panel:
+    Manufacturer: LEN Model 4014 Serial Number 0
+    ASCII string: LTD121EQ3B
+
+* `Lenovo ThinkPad X301`: 0x24fc/264Hz (@320MHz CDClk)
+  LED backlight, panel:
+    Manufacturer: LEN Model 4074 Serial Number 0
+    ASCII string: LTD133EQ1B
+
+## Often copy-pasted constants
+
+* `0x0610 for gm45`: First seen in commit 6481e10
+  "gma45: Ensure that brightness register in gma contains a sane vaule"
+  Depending on the CDClk frequency (222MHz .. 333MHz) 1.12kHz .. 1.61kHz
+
+* `0x0128 for i945`: First seen for lenovo/x60 in commit 26ca08c
+  "i945: Replace video gfx init."
+  With a CDClk of 200MHz it gives a 21.1kHz PWM.