edge: add post for generic sm7150 migration

Signed-off-by: Jens Reidel <adrian@travitia.xyz>

content/edge/2025-03-09-sm7150-generic-migration.md

+title: "Existing SM7150 device packages removed in favour of generic package"
+date: 2025-03-09
+---
+
+## Summary
+
+The device packages for the Xiaomi SM7150 devices in the community category
+(xiaomi-davinci and xiaomi-surya) have been removed in favor of a generic device
+package. Migration requires manual intervention and, in most cases, a reinstall
+from scratch. This is due to the switch to U-Boot as a second stage bootloader
+and a new partition scheme.
+
+## Details
+
+In the past, these devices had device-specific packages that defined which
+devicetree blob would be appended to the kernel and included firmware specific
+to the device, necessitating the packaging of firmware and device package for
+every supported device.
+
+Support for Qualcomm chipsets and devices in U-Boot has been
+[rapidly improving](https://www.linaro.org/blog/initial-u-boot-release-for-qualcomm-platforms/),
+to the point where it is now possible to build and boot U-Boot for SM7150
+devices with very few patches.
+
+The switch to U-Boot as the bootloader for postmarketOS comes with several
+advantages. Most importantly, U-Boot comes with an EFI implementation that lets
+us boot the Linux kernel with systemd-boot and have U-Boot pick the correct
+devicetree blob instead of appending it to the kernel.
+
+This means that as long as a device is supported by the SM7150 Linux kernel fork
+and U-Boot, it can boot postmarketOS with _no changes_ needed in postmarketOS!
+
+Thanks to
+[recent changes in msm-firmware-loader](https://gitlab.postmarketos.org/postmarketOS/msm-firmware-loader/-/tags/1.6.0),
+these devices can now load their firmware from the Android partitions and don't
+require it to be packaged anymore.
+
+This requires some major changes to the partition layout. A default install of
+postmarketOS as found in the prebuilt edge images for these devices currently
+looks something like this:
+
+- The `boot` partition contains an Android boot image with the kernel and
+  devicetree
+- `userdata` or `system` contain the rootfs partition and the boot partition as
+  subpartitions
+
+Going forward, it will look as follows:
+
+- `boot` contains an Android boot image with U-Boot disguised as a Linux kernel
+- `cache` (or any other partition >256MB in size that does not contain firmware)
+  contains the boot partition with the EFI system partition containing U-Boot,
+  the Linux kernel and devicetree blobs for supported devices
+- `userdata` serves as the rootfs partition
+
+These two partition setups are entirely incompatible with each other and there
+is no way to migrate from one to the other without taking a backup and
+performing a fresh install.
+
+Since the SM7150 devices never made it to a stable release, this was deemed
+acceptable and worth the upsides of this migration.
+
+## Performing a fresh install
+
+The steps for performing a new install of a supported SM7150 device are as
+follows (they can also be found
+[in the Wiki](https://wiki.postmarketos.org/wiki/Generic_SM7150_(qcom-sm7150)#Installation)):
+
+1. Reboot the device into fastboot by holding the `Volume Down` and `Power`
+   buttons
+
+2. If you're coming from Android, run `fastboot erase dtbo`. If you were on
+   postmarketOS before, you don't need to run this again.
+
+3. Download the U-Boot image for your device from
+   [the latest release](https://github.com/sm7150-mainline/u-boot/releases/tag/2025-03-09).
+   If your device has multiple options available, consult the postmarketOS Wiki
+   for the steps to determine your panel variant.
+
+4. Flash the U-Boot image:
+   `fastboot flash boot u-boot-sm7150-[vendor]-[device].img`
+
+5. Download a
+   [postmarketOS edge build](https://images.postmarketos.org/bpo/edge/qcom-sm7150/)
+   for the generic SM7150 target and decompress the images with `unxz`.
+
+6. Flash the boot partition to `cache`:
+   `fastboot flash cache <decompressed boot.img>` (this partition may not exist
+   on A/B-partitioned devices, in which case we need to flash to a different
+   partition, check your device's Wiki page for details)
+
+7. Flash the rootfs to `userdata`:
+   `fastboot flash userdata <decompressed qcom-sm7150.img>`
+
+8. Reboot the device: `fastboot reboot`