EDID

Reading EDID

• Install necessary software

sudo apt install read-edid i2c-dev

• Get the devices

sudo get-edid|grep 'buses found'

2 potential busses found: 6 7

Query the interesting bus and get it human readable

sudo get-edid -b 7 | parse-edid

Yes, that's the one!

• Dump the edid

sudo get-edid -b 7 > fosdem_usbc_portable_screen.bin

Dumped edid information for all ms2131 devices we have can be found in the repo.

Finding the edid in the firmware

• Convert the binary edid dump we just made to something more human readable.

xxd edid_hagibis.bin > edid_hagibis.hex

• Dump the device flash and make it human readable

sudo ./cli --log-level=7 read FLASH 0 --filename=/tmp/hagibis_flash_full.bin
xxd /tmp/hagibis_flash_full.bin

• Grep around for the edid info. Find something promising at 0x005a. Dump it from flash.

sudo ./cli --log-level=7 read FLASH 0x005a 256 --filename=/tmp/hagibis_flash_edid.bin

• Compare the edid tool to the 256 bytes from flash. Yay! We have it!

diff edid_hagibis.bin hagibis_flash_edid.bin

Editing EDID

• wxedid
  • Debian: 0.21
  • upstream: 0.29
  • limited
• https://www.analogway.com/emea/products/software-tools/aw-edid-editor/ (non-free)

Getting the device to use a modified EDID

• Naively trying to write the modified EDID to RAM where we found it at 0x1b33:

sudo ./cli write-file RAM 0x1b33 /home/mark/Downloads/edid_hagibis_modified.bin

• This does not yield the expected result:

sudo ./cli read RAM 0x1b33 256 --filename=/tmp/edid_hagibis_modified_reread_from_ram.bin

• Dump the modified EDID into the flash we dumped:

dd if=edid_hagibis_modified.bin of=hagibis_flash_modified_nocrc.bin bs=1 seek=90 conv=notrunc

• Use the firmware checksum update function built by our in-house professional Go programmer to update this ms213x-status binary.

./ms213x-status firmware --filename hagibis_flash_modified_nocrc.bin --mode write

• Check the new crc in the binary:

./ms213x-status firmware --filename hagibis_flash_modified_nocrc.bin

• Upload the new firmware to the device:

sudo ./cli --log-level=7 write-file --verify FLASH 0 /home/mark/Downloads/hagibis_flash_modified_goodcrc.bin