feat(draw): add configurable thread priority for all drawing units (#8162)

Co-authored-by: Liam Howatt <30486941+liamHowatt@users.noreply.github.com>

Kconfig

@@ -207,6 +207,23 @@ menu "LVGL configuration"
 			help
 				If FreeType or ThorVG is enabled, it is recommended to set it to 32KB or more.
 
+		config LV_DRAW_THREAD_PRIO
+			int "Thread priority for the drawing thread"
+			range 0 4
+			default 3
+			depends on LV_USE_OS > 0
+			help
+				Thread priority controls the relative importance of the drawing threads.
+				Values correspond to lv_thread_prio_t enum in lv_os.h:
+				0: LV_THREAD_PRIO_LOWEST
+				1: LV_THREAD_PRIO_LOW
+				2: LV_THREAD_PRIO_MID (default)
+				3: LV_THREAD_PRIO_HIGH
+				4: LV_THREAD_PRIO_HIGHEST
+
+				Higher priority can improve rendering performance but might cause
+				starvation of lower priority tasks.
+
 		config LV_USE_DRAW_SW
 			bool "Enable software rendering"
 			default y

docs/src/details/main-modules/draw/draw_pipeline.rst

@@ -113,6 +113,19 @@ For an example of how draw-unit cration and initialization is done, see
 :cpp:func:`lv_draw_sw_init` in lv_draw_sw.c_ or the other draw units whose ``init``
 functions are optionally called in :cpp:func:`lv_init`.
 
+Thread Priority 
+--------------- 
+
+All draw units operate with a configurable thread priority which can be set using the 
+:c:macro:`LV_DRAW_THREAD_PRIO` configuration option in ``lv_conf.h``. This allows you 
+to fine-tune the priority level across all drawing units, which is especially useful for 
+systems with limited priority levels. 
+
+By default, draw units use :c:macro:`LV_THREAD_PRIO_HIGH` as their thread priority. 
+This consistent approach ensures that all drawing units (software rendering, hardware 
+accelerators like STM32 DMA2D, NXP VGLite, etc.) use the same priority level unless 
+explicitly configured otherwise. 
+
 .. _lv_draw_sw.c:  https://github.com/lvgl/lvgl/blob/master/src/draw/sw/lv_draw_sw.c
 
 
@@ -196,4 +209,4 @@ API
     lv_draw_task_t
     LV_DRAW_TRANSFORM_USE_MATRIX
     lv_draw_unit_t
-    LV_USE_DRAW_OPENGLES
+    LV_USE_DRAW_OPENGLES

lv_conf_template.h

@@ -156,6 +156,15 @@
  */
 #define LV_DRAW_THREAD_STACK_SIZE    (8 * 1024)         /**< [bytes]*/
 
+/** Thread priority of the drawing task.
+ *  Higher values mean higher priority.
+ *  Can use values from lv_thread_prio_t enum in lv_os.h: LV_THREAD_PRIO_LOWEST,
+ *  LV_THREAD_PRIO_LOW, LV_THREAD_PRIO_MID, LV_THREAD_PRIO_HIGH, LV_THREAD_PRIO_HIGHEST
+ *  Make sure the priority value aligns with the OS-specific priority levels.
+ *  On systems with limited priority levels (e.g., FreeRTOS), a higher value can improve
+ *  rendering performance but might cause other tasks to starve. */
+#define LV_DRAW_THREAD_PRIO LV_THREAD_PRIO_HIGH
+
 #define LV_USE_DRAW_SW 1
 #if LV_USE_DRAW_SW == 1
     /*

src/draw/dma2d/lv_draw_dma2d.c

@@ -69,7 +69,7 @@ void lv_draw_dma2d_init(void)
 #if LV_DRAW_DMA2D_ASYNC
     g_unit = draw_dma2d_unit;
 
-    lv_result_t res = lv_thread_init(&draw_dma2d_unit->thread, "dma2d", LV_THREAD_PRIO_HIGH, thread_cb, 2 * 1024,
+    lv_result_t res = lv_thread_init(&draw_dma2d_unit->thread, "dma2d", LV_DRAW_THREAD_PRIO, thread_cb, 2 * 1024,
                                      draw_dma2d_unit);
     LV_ASSERT(res == LV_RESULT_OK);
 #endif

src/draw/nema_gfx/lv_draw_nema_gfx.c

@@ -119,7 +119,7 @@ void lv_draw_nema_gfx_init(void)
 
 
 #if LV_USE_OS
-    lv_thread_init(&draw_nema_gfx_unit->thread, "nemagfx", LV_THREAD_PRIO_HIGH, nema_gfx_render_thread_cb, 2 * 1024,
+    lv_thread_init(&draw_nema_gfx_unit->thread, "nemagfx", LV_DRAW_THREAD_PRIO, nema_gfx_render_thread_cb, 2 * 1024,
                    draw_nema_gfx_unit);
 #endif
 }

src/draw/nxp/g2d/lv_draw_g2d.c

@@ -78,7 +78,7 @@ void lv_draw_g2d_init(void)
         LV_LOG_ERROR("g2d_open fail.\n");
     }
 #if LV_USE_G2D_DRAW_THREAD
-    lv_thread_init(&draw_g2d_unit->thread, "g2ddraw", LV_THREAD_PRIO_HIGH, _g2d_render_thread_cb, 2 * 1024, draw_g2d_unit);
+    lv_thread_init(&draw_g2d_unit->thread, "g2ddraw", LV_DRAW_THREAD_PRIO, _g2d_render_thread_cb, 2 * 1024, draw_g2d_unit);
 #endif
 }
 

src/draw/nxp/pxp/lv_draw_pxp.c

@@ -95,7 +95,7 @@ void lv_draw_pxp_init(void)
     draw_pxp_unit->base_unit.name = "NXP_PXP";
 
 #if LV_USE_PXP_DRAW_THREAD
-    lv_thread_init(&draw_pxp_unit->thread, "pxpdraw", LV_THREAD_PRIO_HIGH, _pxp_render_thread_cb, 2 * 1024, draw_pxp_unit);
+    lv_thread_init(&draw_pxp_unit->thread, "pxpdraw", LV_DRAW_THREAD_PRIO, _pxp_render_thread_cb, 2 * 1024, draw_pxp_unit);
 #endif
 #endif /*LV_USE_DRAW_PXP*/
 }

src/draw/nxp/vglite/lv_draw_vglite.c

@@ -118,7 +118,7 @@ void lv_draw_vglite_init(void)
     draw_vglite_unit->base_unit.name = "NXP_VGLITE";
 
 #if LV_USE_VGLITE_DRAW_THREAD
-    lv_thread_init(&draw_vglite_unit->thread, "vglitedraw", LV_THREAD_PRIO_HIGHEST, _vglite_render_thread_cb, 4 * 1024,
+    lv_thread_init(&draw_vglite_unit->thread, "vglitedraw", LV_DRAW_THREAD_PRIO, _vglite_render_thread_cb, 4 * 1024,
                    draw_vglite_unit);
 #endif
 }

src/draw/renesas/dave2d/lv_draw_dave2d.c

@@ -99,7 +99,7 @@ void lv_draw_dave2d_init(void)
     lv_ll_init(&_ll_Dave2D_Tasks, 4);
 
 #if LV_USE_OS
-    lv_thread_init(&draw_dave2d_unit->thread, "dave2d", LV_THREAD_PRIO_HIGH, _dave2d_render_thread_cb, 8 * 1024,
+    lv_thread_init(&draw_dave2d_unit->thread, "dave2d", LV_DRAW_THREAD_PRIO, _dave2d_render_thread_cb, 8 * 1024,
                    draw_dave2d_unit);
 #endif
 

src/draw/sw/lv_draw_sw.c

@@ -91,7 +91,7 @@ void lv_draw_sw_init(void)
         lv_draw_sw_thread_dsc_t * thread_dsc = &draw_sw_unit->thread_dscs[i];
         thread_dsc->idx = i;
         thread_dsc->draw_unit = (void *) draw_sw_unit;
-        lv_thread_init(&thread_dsc->thread, "swdraw", LV_THREAD_PRIO_HIGH, render_thread_cb,
+        lv_thread_init(&thread_dsc->thread, "swdraw", LV_DRAW_THREAD_PRIO, render_thread_cb,
                        LV_DRAW_THREAD_STACK_SIZE, thread_dsc);
     }
 #endif

src/lv_conf_internal.h

@@ -377,6 +377,21 @@
     #endif
 #endif
 
+/** Thread priority of the drawing task.
+ *  Higher values mean higher priority.
+ *  Can use values from lv_thread_prio_t enum in lv_os.h: LV_THREAD_PRIO_LOWEST,
+ *  LV_THREAD_PRIO_LOW, LV_THREAD_PRIO_MID, LV_THREAD_PRIO_HIGH, LV_THREAD_PRIO_HIGHEST
+ *  Make sure the priority value aligns with the OS-specific priority levels.
+ *  On systems with limited priority levels (e.g., FreeRTOS), a higher value can improve
+ *  rendering performance but might cause other tasks to starve. */
+#ifndef LV_DRAW_THREAD_PRIO
+    #ifdef CONFIG_LV_DRAW_THREAD_PRIO
+        #define LV_DRAW_THREAD_PRIO CONFIG_LV_DRAW_THREAD_PRIO
+    #else
+        #define LV_DRAW_THREAD_PRIO LV_THREAD_PRIO_HIGH
+    #endif
+#endif
+
 #ifndef LV_USE_DRAW_SW
     #ifdef LV_KCONFIG_PRESENT
         #ifdef CONFIG_LV_USE_DRAW_SW