esp32: make WiFi IRAM optimization configurable

With this feature, the WiFi IRAM optimization can be disabled/enabled via menuconfig.

components/esp32/CMakeLists.txt

@@ -72,6 +72,14 @@ else()
     register_component()
 
     target_link_libraries(esp32 "-L ${CMAKE_CURRENT_SOURCE_DIR}/lib")
+
+    # Add a different linker search path depending on WiFi optimisations
+    if (CONFIG_ESP32_WIFI_IRAM_OPT)
+        target_link_libraries(esp32 "-L ${CMAKE_CURRENT_SOURCE_DIR}/ld/wifi_iram_opt")
+    else()
+        target_link_libraries(esp32 "-L ${CMAKE_CURRENT_SOURCE_DIR}/ld/wifi_iram_noopt")
+    endif()
+
     if(NOT CONFIG_NO_BLOBS)
         target_link_libraries(esp32 coexist core espnow mesh net80211 phy pp rtc smartconfig wpa2 wpa wps)
     endif()

components/esp32/Kconfig

@@ -1152,7 +1152,14 @@ config ESP32_WIFI_SOFTAP_BEACON_MAX_LEN
         932 (752+36*5).
         
         Setting a longer beacon length also assists with debugging as the conflicting root nodes can be identified more quickly.
-        
+
+config ESP32_WIFI_IRAM_OPT
+    bool "WiFi IRAM speed optimization"
+    default y
+    help
+        Select this option to place frequently called Wi-Fi library functions in IRAM. When this option is disabled,
+        more than 10Kbytes of IRAM memory will be saved but Wi-Fi throughput will be reduced.
+
 endmenu  # Wi-Fi
 
 menu PHY

components/esp32/component.mk

@@ -18,6 +18,13 @@ endif
 #specifies its own scripts.
 LINKER_SCRIPTS += esp32.common.ld esp32.rom.ld esp32.peripherals.ld
 
+# Add a different linker search path depending on WiFi optimisations
+ifdef CONFIG_ESP32_WIFI_IRAM_OPT
+COMPONENT_ADD_LDFLAGS += -L $(COMPONENT_PATH)/ld/wifi_iram_opt
+else
+COMPONENT_ADD_LDFLAGS += -L $(COMPONENT_PATH)/ld/wifi_iram_noopt
+endif
+
 #Force pure functions from libgcc.a to be linked from ROM
 LINKER_SCRIPTS += esp32.rom.libgcc.ld
 

components/esp32/ld/esp32.common.ld

@@ -159,6 +159,7 @@ SECTIONS
     *libheap.a:multi_heap_poisoning.*(.literal .text .literal.* .text.*)
     *libesp32.a:panic.*(.literal .text .literal.* .text.*)
     *libesp32.a:core_dump.*(.literal .text .literal.* .text.*)
+    INCLUDE wifi_iram.ld
     *libapp_trace.a:(.literal .text .literal.* .text.*)
     *libxtensa-debug-module.a:eri.*(.literal .text .literal.* .text.*)
     *librtc.a:(.literal .text .literal.* .text.*)
@@ -326,6 +327,7 @@ SECTIONS
     _text_start = ABSOLUTE(.);
     *(.literal .text .literal.* .text.* .stub .gnu.warning .gnu.linkonce.literal.* .gnu.linkonce.t.*.literal .gnu.linkonce.t.*)
     *(.irom0.text) /* catch stray ICACHE_RODATA_ATTR */
+    *(.wifi0iram .wifi0iram.*) /* catch stray WIFI_IRAM_ATTR */
     *(.fini.literal)
     *(.fini)
     *(.gnu.version)

components/esp32/ld/wifi_iram_noopt/wifi_iram.ld

@@ -0,0 +1,2 @@
+/* This snippet does nothing, if WiFi IRAM optimisations
+   are disabled. */

components/esp32/ld/wifi_iram_opt/wifi_iram.ld

@@ -0,0 +1,4 @@
+/* Link WiFi library .wifi0iram sections to IRAM
+   if this snippet is included */
+*libnet80211.a:( .wifi0iram  .wifi0iram.*)
+*libpp.a:( .wifi0iram  .wifi0iram.*)