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Document os_prefix, overlay_prefix, upstream_kernel #1433

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merged 3 commits into from
Mar 19, 2020
Merged

Document os_prefix, overlay_prefix, upstream_kernel #1433

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29c53e2
Document os_prefix, overlay_prefix, upstream_kernel
Mar 13, 2020
edca9bb
Make it clear that os_prefix is optional
Mar 19, 2020
8905bde
Clarification of upstream_kernel semantics
Mar 19, 2020
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4 changes: 2 additions & 2 deletions configuration/config-txt/boot.md
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Expand Up @@ -128,8 +128,8 @@ Be aware that output is likely to interfere with Bluetooth operation unless it i
## upstream_kernel
<a name="upstream_kernel">

If `upstream_kernel=1` is used, the firmware will choose the upstream Linux names for DTBs (`bcm2835-rpi-b.dtb` instead of `bcm2708-rpi-b.dtb`, for example). It will also set [`os_prefix`](#os_prefix) to "upstream/", unless it has been explicitly set to something else, but like other `os_prefix` values it will be ignored if the required kernel and .dtb file can't be found when using the prefix.
If `upstream_kernel=1` is used, the firmware sets [`os_prefix`](#os_prefix) to "upstream/", unless it has been explicitly set to something else, but like other `os_prefix` values it will be ignored if the required kernel and .dtb file can't be found when using the prefix.

To allow a common DTB to be used, if the upstream file isn't found the firmware will load the downstream variant instead and automatically apply the "upstream" overlay.
The firmware will also prefer upstream Linux names for DTBs (`bcm2837-rpi-3-b.dtb` instead of `bcm2710-rpi-3-b.dtb`, for example). If the upstream file isn't found the firmware will load the downstream variant instead and automatically apply the "upstream" overlay to make some adjustments. Note that this process happens _after_ the `os_prefix` has been finalised.
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Does the "upstream overlay" have a specific filename that could be mentioned here, or is it more complex than that?

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Yes, upstream.

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Not upstream.dtbo ?

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Don't confuse the name of the overlay with the name of the file.

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That's kinda what I was getting at - perhaps it should say:
and automatically apply the "upstream" overlay (upstream.dtbo) to make some adjustments.

?

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I don't see the point of emphasising the filename - overlays are referred to by name, not by filename. The overlay filename convention has changed before, but the names of the overlays didn't have to.

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Fair enough - as somebody unfamiliar with DeviceTree, I had no clue what apply the "upstream" overlay was inferring. But I guess others are probably less clueless than me 😁


*This article uses content from the eLinux wiki page [RPiconfig](http://elinux.org/RPiconfig), which is shared under the [Creative Commons Attribution-ShareAlike 3.0 Unported license](http://creativecommons.org/licenses/by-sa/3.0/)*