expand edid override text

edid-override.md

@@ -41,7 +41,9 @@ Linux provides direct access to the EDID data as a file, per display output of t
 
 To remove the YUV mode, the EDID may be transformed to a human readable format, edited and transformed back by an appropriate tool, or the data may be edited directly with a hex editor.
 
-cros-chameleon is one such python tool that transforms edid data to human readable json and back.
+The `wxEDID` GUI application can be used to change all values of `YCbCr420`, `YCbCr444` and similar to `0`.
+
+Alternatively the `cros-chameleon` command line tool can transform edid data to human readable json and back.
 
 ```
 git clone https://github.com/rpavlik/cros-chameleon.git
@@ -64,6 +66,14 @@ and convert the fixed json back to edid data:
 
 #### Overriding the EDID
 
-Place the edid in /lib/firmware/edid/, for example `/lib/firmware/edid/override.edid`. You may need to regenerate your initramfs to include the firmware files.
+Create a directory in /lib/firmware for the edid `sudo mkdir -p /lib/firmware/edid/`.
+
+Place the edid file in `/lib/firmware/edid/`, for example `/lib/firmware/edid/override.edid`.
+
+You may need to regenerate your initramfs to include the firmware files. On Ubuntu this is done with `update-initramfs -u -k all`.
+
+Append `drm.edid_firmware=HDMI-A-1:edid/override.edid` to your kernel command line. Most default installations will use grub as boot loader. Edit `/etc/default/grub` and add the override string to `GRUB_CMDLINE_LINUX_DEFAULT` so it looks like `GRUB_CMDLINE_LINUX_DEFAULT="quiet drm.edid_firmware=HDMI-A-1:edid/override.edid"`. Replace HDMI-A-1 with the appropriate output name found in `/sys/class/drm/card*-*`.
+
+On kernels older than 4.13, replace `drm.edid_firmware=` with `drm_kms_helper.edid_firmware=`.
 
-Append `drm.edid_firmware=HDMI-A-1:edid/override.edid` to your kernel command line. Replace HDMI-A-1 with the appropriate output name found in `/sys/class/drm/card*-*`.
+Generate an updated grub configuration from the /etc/default/grub template: `sudo grub-mkconfig -o /boot/grub/grub.cfg` and reboot.