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Add information on setting up Touch Display 2 on Compute Modules #4072

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3b82220
Add information on setting up TD2 on Compute modules
JamesH65 Apr 16, 2025
e8a4aa7
Updated from review comments
JamesH65 Apr 17, 2025
6d5f683
Updated after review comments
JamesH65 Apr 22, 2025
7066020
Fix xref URL
lurch Apr 23, 2025
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4 changes: 4 additions & 0 deletions documentation/asciidoc/accessories/display/display_intro.adoc
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Expand Up @@ -159,3 +159,7 @@ To specify these options, add them, separated by commas, to your `dtoverlay` lin
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dtoverlay=vc4-kms-dsi-7inch,sizex=400,invx,invy
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=== Installation on Compute Module based devices.

All Raspberry Pi SBCs auto-detect the official Touch Displays as the circuitry connecting it to the DSI connector is fixed; this autodetection ensures the correct Device Tree entries are passed to the kernel. However, Compute Modules are intended for industrial applications where the integrator can use any and all GPIOs and interfaces for whatever purposes they require. Autodetection is therefore not feasible, and hence is disabled on Compute Module devices. This means that the Device Tree fragments required to set up the display need to be loaded via some other mechanism, which can be either with a dtoverlay entry in config.txt as described above, via a custom base DT file, or if present, a HAT EEPROM.
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IMHO "All Raspberry Pi SBCs auto-detect the official Touch Displays as the circuitry connecting it to the DSI connector is fixed;" makes it sound like it's the circuitry between the Touch Display and the DSI connector which is fixed? Which is obviously also true for the CMs 😉
Perhaps "All Raspberry Pi SBCs auto-detect the official Touch Displays as the circuitry connected to the DSI connector on the Raspberry Pi board is fixed;" ?

7 changes: 7 additions & 0 deletions documentation/asciidoc/accessories/touch-display-2/about.adoc
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Expand Up @@ -127,3 +127,10 @@ To specify these options, add them, separated by commas, to your `dtoverlay` lin
----
dtoverlay=vc4-kms-dsi-ili9881-7inch,sizex=400,invx,invy
----

=== Installation and software setup on Compute Module based devices.

All Raspberry Pi SBCs auto-detect the official Touch Displays as the circuitry connecting it to the DSI connector is fixed; this autodetection ensures the correct Device Tree entries are passed to the kernel. However, Compute Modules are intended for industrial applications where the integrator can use any and all GPIOs and interfaces for whatever purposes they require. Autodetection is therefore not feasible, and hence is disabled on Compute Module devices. This means that the Device Tree fragments required to set up the display need to be loaded via some other mechanism, which can be either with a dtoverlay entry in config.txt, via a custom base DT file, or if present, a HAT EEPROM.

Creating a custom base Device tree file is beyond the scope of this documentation, however, it is simple to add an appropriate device tree entry via `config.txt`. See this xref:../computers/compute-module.adoc#attaching-the-touch-display-2-lcd-panel[page] for configuration details.

18 changes: 18 additions & 0 deletions documentation/asciidoc/computers/compute-module/cmio-display.adoc
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Expand Up @@ -61,3 +61,21 @@ To entirely ignore the display when connected, add the following line to `/boot/
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ignore_lcd=1
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== Attaching the Touch Display 2 LCD panel

Touch Display 2 is a 720x1280 7" LCD display designed specifically for Raspberry Pi devices (see https://www.raspberrypi.com/products/touch-display-2/). It connects in much the same way as the original touch display, but the software setup on Compute Modules is slightly different as it uses a different display driver. See xref:../accessories/touch-display-2.adoc[Touch Display 2] for connection details.

Edit the /boot/firmware/config.txt file and add the following to enable Touch Display 2 on DSI1.

[source,ini]
----
dtoverlay=vc4-kms-dsi-ili9881-7inch
----

To use DSI0 use the following:

[source,ini]
----
dtoverlay=vc4-kms-dsi-ili9881-7inch,dsi0
----
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