[Mellanox] Place FW binaries under platform directory instead of squashfs (#13837)

Fixes #13568

Upgrade from old image always requires squashfs mount to get the next image FW binary. This can be avoided if we put FW binary under platform directory which is easily accessible after installation:

admin@r-spider-05:~$ ls /host/image-fw-new-loc.0-dirty-20230208.193534/platform/fw-SPC.mfa
/host/image-fw-new-loc.0-dirty-20230208.193534/platform/fw-SPC.mfa
admin@r-spider-05:~$ ls -al /tmp/image-fw-new-loc.0-dirty-20230208.193534-fs/etc/mlnx/fw-SPC.mfa
lrwxrwxrwx 1 root root 66 Feb  8 17:57 /tmp/image-fw-new-loc.0-dirty-20230208.193534-fs/etc/mlnx/fw-SPC.mfa -> /host/image-fw-new-loc.0-dirty-20230208.193534/platform/fw-SPC.mfa

- Why I did it
202211 and above uses different squashfs compression type that 201911 kernel can not handle. Therefore, we avoid mounting squashfs altogether with this change.

- How I did it
Place FW binary under /host/image-/platform/mlnx/, soft links in /etc/mlnx are created to avoid breaking existing scripts/automation.
/etc/mlnx/fw-SPCX.mfa is a soft link always pointing to the FW that should be used in current image
mlnx-fw-upgrade.sh is updated to prefer /host/image-/platform/mlnx location and fallback to /etc/mlnx in squashfs in case new location does not exist. This is necessary to do image downgrade.

- How to verify it
Upgrade from 201911 to master
master to 201911 downgrade
master -> master reboot
ONIE -> master boot (First FW burn)
Which release branch to backport (provide reason below if selected)

files/build_templates/sonic_debian_extension.j2

@@ -928,10 +928,18 @@ sudo cp {{src}} $FILESYSTEM_ROOT/{{dst}}
 {% endfor -%}
 
 {% if sonic_asic_platform == "mellanox" %}
-sudo mkdir -p $FILESYSTEM_ROOT/etc/mlnx/
-sudo cp $files_path/$MLNX_SPC_FW_FILE $FILESYSTEM_ROOT/etc/mlnx/fw-SPC.mfa
-sudo cp $files_path/$MLNX_SPC2_FW_FILE $FILESYSTEM_ROOT/etc/mlnx/fw-SPC2.mfa
-sudo cp $files_path/$MLNX_SPC3_FW_FILE $FILESYSTEM_ROOT/etc/mlnx/fw-SPC3.mfa
+declare -rA FW_FILE_MAP=( \
+    [$MLNX_SPC_FW_FILE]="fw-SPC.mfa" \
+    [$MLNX_SPC2_FW_FILE]="fw-SPC2.mfa" \
+    [$MLNX_SPC3_FW_FILE]="fw-SPC3.mfa" \
+)
+sudo mkdir -p $FILESYSTEM_ROOT/$PLATFORM_DIR/fw/asic/
+sudo mkdir -p $FILESYSTEM_ROOT_ETC/mlnx/
+for fw_file_name in ${!FW_FILE_MAP[@]}; do
+    sudo cp $files_path/$fw_file_name $FILESYSTEM_ROOT/$PLATFORM_DIR/fw/asic/${FW_FILE_MAP[$fw_file_name]}
+    # Link old FW location to not break existing automation/scripts
+    sudo ln -s /host/image-$SONIC_IMAGE_VERSION/$PLATFORM_DIR/fw/asic/${FW_FILE_MAP[$fw_file_name]} $FILESYSTEM_ROOT/etc/mlnx/${FW_FILE_MAP[$fw_file_name]}
+done
 sudo cp $files_path/$ISSU_VERSION_FILE $FILESYSTEM_ROOT/etc/mlnx/issu-version
 sudo cp $files_path/$MLNX_FFB_SCRIPT $FILESYSTEM_ROOT/usr/bin/mlnx-ffb.sh
 sudo cp $files_path/$MLNX_ONIE_FW_UPDATE $FILESYSTEM_ROOT/usr/bin/$MLNX_ONIE_FW_UPDATE

platform/mellanox/mlnx-fw-upgrade.j2

@@ -32,9 +32,9 @@ declare -r UNKN_ASIC="unknown"
 declare -r UNKN_MST="unknown"
 
 declare -rA FW_FILE_MAP=( \
-    [$SPC1_ASIC]="/etc/mlnx/fw-SPC.mfa" \
-    [$SPC2_ASIC]="/etc/mlnx/fw-SPC2.mfa" \
-    [$SPC3_ASIC]="/etc/mlnx/fw-SPC3.mfa" \
+    [$SPC1_ASIC]="fw-SPC.mfa" \
+    [$SPC2_ASIC]="fw-SPC2.mfa" \
+    [$SPC3_ASIC]="fw-SPC3.mfa" \
 )
 
 IMAGE_UPGRADE="${NO_PARAM}"
@@ -221,17 +221,17 @@ function RunFwUpdateCmd() {
 }
 
 function UpgradeFW() {
-    local -r _FS_MOUNTPOINT="$1"
+    local -r _FW_BIN_PATH="$1"
 
     local -r _ASIC_TYPE="$(GetAsicType)"
     if [[ "${_ASIC_TYPE}" = "${UNKN_ASIC}" ]]; then
         ExitFailure "failed to detect ASIC type"
     fi
 
-    if [ ! -z "${_FS_MOUNTPOINT}" ]; then
-        local -r _FW_FILE="${_FS_MOUNTPOINT}/${FW_FILE_MAP[$_ASIC_TYPE]}"
+    if [ ! -z "${_FW_BIN_PATH}" ]; then
+        local -r _FW_FILE="${_FW_BIN_PATH}/${FW_FILE_MAP[$_ASIC_TYPE]}"
     else
-        local -r _FW_FILE="${FW_FILE_MAP[$_ASIC_TYPE]}"
+        local -r _FW_FILE="/etc/mlnx/${FW_FILE_MAP[$_ASIC_TYPE]}"
     fi
 
     if [ ! -f "${_FW_FILE}" ]; then
@@ -274,16 +274,29 @@ function UpgradeFWFromImage() {
     local -r _NEXT_SONIC_IMAGE="$(sonic-installer list | grep "Next: " | cut -f2 -d' ')"
     local -r _CURRENT_SONIC_IMAGE="$(sonic-installer list | grep "Current: " | cut -f2 -d' ')"
 
-    local -r _FS_PATH="/host/image-${_NEXT_SONIC_IMAGE#SONiC-OS-}/fs.squashfs"
-    local -r _FS_MOUNTPOINT="/tmp/image-${_NEXT_SONIC_IMAGE#SONiC-OS-}-fs"
-
     if [[ "${_CURRENT_SONIC_IMAGE}" == "${_NEXT_SONIC_IMAGE}" ]]; then
         ExitSuccess "firmware is up to date"
+    fi
+
+    # /host/image-<version>/platform/fw/asic is now the new location for FW binaries.
+    # Prefere this path and if it does not exist use squashfs as a fallback.
+    local -r _PLATFORM_FW_BIN_PATH="/host/image-${_NEXT_SONIC_IMAGE#SONiC-OS-}/platform/fw/asic/"
+
+    if [[ -d "${_PLATFORM_FW_BIN_PATH}" ]]; then
+        LogInfo "Using FW binaries from ${_PLATFORM_FW_BIN_PATH}"
+
+        UpgradeFW "${_PLATFORM_FW_BIN_PATH}"
     else
+        local -r _FS_PATH="/host/image-${_NEXT_SONIC_IMAGE#SONiC-OS-}/fs.squashfs"
+        local -r _FS_MOUNTPOINT="/tmp/image-${_NEXT_SONIC_IMAGE#SONiC-OS-}-fs"
+        local -r _FW_BIN_PATH="${_FS_MOUNTPOINT}/etc/mlnx/"
+
+        LogInfo "Using FW binaries from ${_FW_BIN_PATH}"
+
         mkdir -p "${_FS_MOUNTPOINT}"
         mount -t squashfs "${_FS_PATH}" "${_FS_MOUNTPOINT}"
 
-        UpgradeFW "${_FS_MOUNTPOINT}"
+        UpgradeFW "${_FW_BIN_PATH}"
 
         umount -rf "${_FS_MOUNTPOINT}"
         rm -rf "${_FS_MOUNTPOINT}"