main/linux-postmarketos-qcom-msm8916: build for armv7 (!828)

Unfortunately, early firmware versions on MSM8916 (used together with
Android 4.4) are not capable of booting aarch64 kernels. MSM8916 was
Qualcomm's first 64-bit capable CPU, and back when it was introduced
Android did not even support aarch64 yet. So the aarch64 capable
hardware was usually used together with armv7 binaries.

To make things worse, this firmware is also signed (usually per-device),
making it (currently) impossible to update it without help from the manufacturer.
This means that we are currently unable to run mainline on devices
that never received an update to Android 5.0
(e.g. the Samsung Galaxy S4 Mini Value Edition).

One way to circumvent this limitation is to build mainline for armv7.
This works surprisingly well with some additional fixes.
Devices with this firmware limitation are still unable to use aarch64
binaries, but at least we can run mainline on them!

main/linux-postmarketos-qcom-msm8916/APKBUILD

@@ -6,14 +6,19 @@ pkgname="linux-${_flavor}"
 pkgver=5.5_rc3
 pkgrel=0
 pkgdesc="Mainline kernel fork for Qualcomm MSM8916 devices"
-arch="aarch64"
-_carch="arm64"
+arch="aarch64 armv7"
 url="https://github.com/msm8916-mainline/linux"
 license="GPL-2.0-only"
 options="!strip !check !tracedeps"
 depends_dev="perl gmp-dev elfutils-dev bash flex bison"
 makedepends="$depends_dev sed installkernel bc linux-headers openssl-dev dtbtool"
 
+# Architecture
+case "$CARCH" in
+	aarch64) _carch="arm64" ;;
+	arm*)    _carch="arm" ;;
+esac
+
 # Compiler: latest GCC from Alpine
 HOSTCC="${CC:-gcc}"
 HOSTCC="${HOSTCC#${CROSS_COMPILE}}"
@@ -22,13 +27,14 @@ HOSTCC="${HOSTCC#${CROSS_COMPILE}}"
 _tag=v${pkgver//_/-}-msm8916
 source="
 	$pkgname-$_tag.tar.gz::$url/archive/$_tag.tar.gz
-	config-$_flavor.$arch
+	config-$_flavor.aarch64
+	config-$_flavor.armv7
 "
 builddir="$srcdir/linux-${_tag#v}"
 
 prepare() {
 	default_prepare
-	cp "$srcdir/config-$_flavor.$arch" .config
+	cp "$srcdir/config-$_flavor.$CARCH" .config
 }
 
 build() {
@@ -50,9 +56,10 @@ package() {
 		"$pkgdir"/usr/share/kernel/$_flavor/kernel.release
 
 	# Master DTB (deviceinfo_bootimg_qcdt)
-	dtbTool -p scripts/dtc/ -o arch/arm64/boot/dt.img arch/arm64/boot/
-	install -Dm644 arch/arm64/boot/dt.img "$pkgdir"/boot/dt.img
+	dtbTool -p scripts/dtc/ -o "arch/$_carch/boot"/dt.img "arch/$_carch/boot/"
+	install -Dm644 "arch/$_carch/boot"/dt.img "$pkgdir"/boot/dt.img
 }
 
 sha512sums="f812b03b83d77b51ee4d99ed22b955bd8a6ae714e4dd171d7798975cf0e5ce30067748655ff5ae052aeb8941d9f4d6a9c10b8bccd997a8f5cff9b16553fd3ea7  linux-postmarketos-qcom-msm8916-v5.5-rc3-msm8916.tar.gz
-ef2a21d00e781a69cc6f800b6097a36b8a4bd656bd3d72ccb999a4fb6f7123adaf5c24511089b98545d3e46746353b30025cd174dc7eff98f793362e4331aa7c  config-postmarketos-qcom-msm8916.aarch64"
+ef2a21d00e781a69cc6f800b6097a36b8a4bd656bd3d72ccb999a4fb6f7123adaf5c24511089b98545d3e46746353b30025cd174dc7eff98f793362e4331aa7c  config-postmarketos-qcom-msm8916.aarch64
+8dc4f6242a3f2022f38741113bfc9b4737c6e94b4544914c8f441c4c83ca91c56e31258077bdb4fdb1e5fa80a79b62bb28e1cbbb43042df4e75ec6fe5bc1caef  config-postmarketos-qcom-msm8916.armv7"