apex: prebuilt_firmware installs in /etc/firmware

Installation path of prebuilt_firmware varies accoding to target
partitions. When it is for system, it installs a file in
/system/etc/firmware while it installs in /vendor/firmware for vendor.

We'd better be consistent about installation path when it is
for APEXes regardless of target partition. Otherwise, ueventd would need
to scan both /apex/*/etc/firmware and /apex/*/firmware.

Having /etc prefix for prebuilt modules helps module owners to predict
the layout of the contents.

Bug: 162701747
Bug: 167942098
Test: soong tests
Test: loading vibrator firmware from vibrator apex (sunfish)
Change-Id: I7a7105026426f8a7a156bc947304930f761c81f3

apex/apex_test.go

@@ -2282,30 +2282,40 @@ func TestVendorApex_use_vndk_as_stable(t *testing.T) {
 	ensureListContains(t, requireNativeLibs, ":vndk")
 }
 
-func TestVendorApex_withPrebuiltFirmware(t *testing.T) {
-	ctx, _ := testApex(t, `
-		apex {
-			name: "myapex",
-			key: "myapex.key",
-			prebuilts: ["myfirmware"],
-			vendor: true,
-		}
-		apex_key {
-			name: "myapex.key",
-			public_key: "testkey.avbpubkey",
-			private_key: "testkey.pem",
-		}
-		prebuilt_firmware {
-			name: "myfirmware",
-			src: "myfirmware.bin",
-			filename_from_src: true,
-			vendor: true,
-		}
-	`)
-
-	ensureExactContents(t, ctx, "myapex", "android_common_myapex_image", []string{
-		"firmware/myfirmware.bin",
-	})
+func TestApex_withPrebuiltFirmware(t *testing.T) {
+	testCases := []struct {
+		name           string
+		additionalProp string
+	}{
+		{"system apex with prebuilt_firmware", ""},
+		{"vendor apex with prebuilt_firmware", "vendor: true,"},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			ctx, _ := testApex(t, `
+				apex {
+					name: "myapex",
+					key: "myapex.key",
+					prebuilts: ["myfirmware"],
+					`+tc.additionalProp+`
+				}
+				apex_key {
+					name: "myapex.key",
+					public_key: "testkey.avbpubkey",
+					private_key: "testkey.pem",
+				}
+				prebuilt_firmware {
+					name: "myfirmware",
+					src: "myfirmware.bin",
+					filename_from_src: true,
+					`+tc.additionalProp+`
+				}
+			`)
+			ensureExactContents(t, ctx, "myapex", "android_common_myapex_image", []string{
+				"etc/firmware/myfirmware.bin",
+			})
+		})
+	}
 }
 
 func TestAndroidMk_UseVendorRequired(t *testing.T) {

etc/prebuilt_etc.go

@@ -172,13 +172,7 @@ func (p *PrebuiltEtc) SubDir() string {
 }
 
 func (p *PrebuiltEtc) BaseDir() string {
-	// If soc install dir was specified and SOC specific is set, set the installDirPath to the specified
-	// socInstallDirBase.
-	installBaseDir := p.installDirBase
-	if p.SocSpecific() && p.socInstallDirBase != "" {
-		installBaseDir = p.socInstallDirBase
-	}
-	return installBaseDir
+	return p.installDirBase
 }
 
 func (p *PrebuiltEtc) Installable() bool {
@@ -205,7 +199,13 @@ func (p *PrebuiltEtc) GenerateAndroidBuildActions(ctx android.ModuleContext) {
 		ctx.PropertyErrorf("sub_dir", "relative_install_path is set. Cannot set sub_dir")
 	}
 
-	p.installDirPath = android.PathForModuleInstall(ctx, p.BaseDir(), p.SubDir())
+	// If soc install dir was specified and SOC specific is set, set the installDirPath to the specified
+	// socInstallDirBase.
+	installBaseDir := p.installDirBase
+	if p.SocSpecific() && p.socInstallDirBase != "" {
+		installBaseDir = p.socInstallDirBase
+	}
+	p.installDirPath = android.PathForModuleInstall(ctx, installBaseDir, p.SubDir())
 
 	// This ensures that outputFilePath has the correct name for others to
 	// use, as the source file may have a different name.