v3/ec/docs: update docs with new functionality

Update the main README to remove notes about some of the chips on
the I2C_1 bus, and to clarify that `stm32reset` will be going away
on Proto 1.
Update the videomux documentation to show the DisplayPort to IT68051
functionality working.

BUG=b:162915510
TEST=Build the firmware as directed in README and flash to the board.
Do the steps in the "DisplayPort to IT68051" section of videomux to
see it working.

Change-Id: I8d4ac7cdfb127177fb223af12e7f35cd1b42983a
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/chameleon/+/2743530
Tested-by: Paul Fagerburg <pfagerburg@chromium.org>
Reviewed-by: Alexandru M Stan <amstan@chromium.org>
Commit-Queue: Paul Fagerburg <pfagerburg@chromium.org>
diff --git a/v3/ec/doc/README.md b/v3/ec/doc/README.md
index d0eacc8..3fae21e 100644
--- a/v3/ec/doc/README.md
+++ b/v3/ec/doc/README.md
@@ -58,7 +58,7 @@
 
 To use the serial bootloader to update the STM32's firmware, you must install
 `stm32flash` and build `stm32reset`. For now all of these things have to do be done outside
-the chroot and some commands (eg. stm32reset) might be deprecated beyond proto0.
+the chroot and some commands (eg. stm32reset) will be deprecated beyond proto0.
 
 ```
 sudo apt-get install stm32flash gpiod libgpiod-dev
@@ -425,8 +425,3 @@
 70: -- -- -- 73 -- -- -- --
 1 devices found on I2C_1
 ```
-
-If you set the I2C switch to 0 or 1, only the MAX7637 shows up in the scan.
-I don't know why the PS8468, PS8469, and MCDP2900 do not respond to the scan
-right now; they might be held in reset because I haven't gotten to the code
-to manage those chips yet.
diff --git a/v3/ec/doc/images/PXL_20210309_192958100_small.png b/v3/ec/doc/images/PXL_20210309_192958100_small.png
new file mode 100644
index 0000000..cbf6237
--- /dev/null
+++ b/v3/ec/doc/images/PXL_20210309_192958100_small.png
Binary files differ
diff --git a/v3/ec/doc/images/PXL_20210309_193029591_small.png b/v3/ec/doc/images/PXL_20210309_193029591_small.png
new file mode 100644
index 0000000..dc42948
--- /dev/null
+++ b/v3/ec/doc/images/PXL_20210309_193029591_small.png
Binary files differ
diff --git a/v3/ec/doc/images/Screenshot_20210309_122751_small.png b/v3/ec/doc/images/Screenshot_20210309_122751_small.png
new file mode 100644
index 0000000..62317b0
--- /dev/null
+++ b/v3/ec/doc/images/Screenshot_20210309_122751_small.png
Binary files differ
diff --git a/v3/ec/doc/videomux.md b/v3/ec/doc/videomux.md
index 880a048..b376c0d 100644
--- a/v3/ec/doc/videomux.md
+++ b/v3/ec/doc/videomux.md
@@ -81,3 +81,50 @@
 HDMI1: n/c
 HDMI2: FPGA
 ```
+
+## DisplayPort to IT68051
+
+The Proto 0 board can connect either DisplayPort connector to the IT68051
+HDMI receiver IC. By default, DP2 is enabled.
+
+Connect a USB-C DisplayPort adapter to a Chromebook
+
+![USB-C DisplayPort adapter](images/PXL_20210309_192958100_small.png "USB-C DisplayPort adapter")
+
+Connect the DisplayPort cable to DP2 (furthest from the USB-C connectors)
+
+![DisplayPort cable connected to DP2](images/PXL_20210309_193029591_small.png "DisplayPort cable connected to DP2")
+
+The Chromebook will recognizes an external display named "ITE6802" with
+various resolutions available up to 4K.
+
+![ITE6802 'Monitor'](images/Screenshot_20210309_122751_small.png "ITE6802 'Monitor'")
+
+To switch to the other DisplayPort, type the following commands in the
+EC shell:
+```
+videomux dp1 rx
+it68051 select 1
+it68051 hpd 1 1
+```
+
+To switch back to DisplayPort 2, type the following commands:
+```
+videomux dp1 rx
+it68051 select 0
+it68051 hpd 0 1
+```
+**Note**: The IT68051 numbers its ports 0 and 1, while the DisplayPort
+connectors are numbered 1 and 2. DP1 connects to the IT68051's port 1, and
+DP2 connects to the IT68051's port **0**.
+
+To hold the IT68051 in reset (disabling the external display),
+```
+io set IT68051_RST_L 0
+```
+
+To release reset and re-initialize the IT68051,
+```
+io set IT68051_RST_L 1
+it68051 init
+```