Merge branch 'feat/dsi_bridge_new_feat' into 'master'

feat(dsi): More DPHY Clock sources supported on ESP32-P4 ECO5

Closes IDF-13537 and IDF-13538

See merge request espressif/esp-idf!41766

Author: suda-morris

.pre-commit-config.yaml

@@ -31,6 +31,7 @@ repos:
             .*.pb-c.c|
             .*.yuv|
             .*.rgb|
+            .*.gray|
             .*COPYING.*|
             docs/sphinx-known-warnings\.txt
           )$

components/esp_lcd/Kconfig

@@ -1,10 +1,4 @@
 menu "ESP-Driver:LCD Controller Configurations"
-    config LCD_ENABLE_DEBUG_LOG
-        bool "Enable debug log"
-        default n
-        help
-            whether to enable the debug log message for LCD driver.
-            Note that, this option only controls the LCD driver log, won't affect other drivers.
 
     if SOC_LCD_RGB_SUPPORTED
         config LCD_RGB_ISR_IRAM_SAFE
@@ -28,14 +22,37 @@ menu "ESP-Driver:LCD Controller Configurations"
     endif # SOC_LCD_RGB_SUPPORTED
 
     if SOC_MIPI_DSI_SUPPORTED
-        config LCD_DSI_ISR_IRAM_SAFE
-            bool "DSI LCD ISR IRAM-Safe"
-            default n
+        config LCD_DSI_ISR_HANDLER_IN_IRAM
+            bool "Place DSI ISR handler in IRAM to reduce latency"
+            default y
+            select LCD_DSI_OBJ_FORCE_INTERNAL
+            help
+                Place DSI ISR handler in IRAM to reduce latency caused by cache miss.
+
+        config LCD_DSI_ISR_CACHE_SAFE
+            bool "Allow DSI ISR to execute when cache is disabled" if !SPI_FLASH_AUTO_SUSPEND
+            select LCD_DSI_ISR_HANDLER_IN_IRAM
             select DW_GDMA_ISR_IRAM_SAFE # relies on DW_GDMA Full trans done interrupt
+            default n
             help
-                Ensure the LCD interrupt is IRAM-Safe by allowing the interrupt handler to be
-                executable when the cache is disabled (e.g. SPI Flash write).
-                If you want the LCD driver to keep flushing the screen even when cache ops disabled,
-                you can enable this option. Note, this will also increase the IRAM usage.
+                Enable this option to allow the DSI Interrupt Service Routine (ISR)
+                to execute even when the cache is disabled. This can be useful in scenarios where the cache
+                might be turned off, but the DSI functionality is still required to operate correctly.
+
+        config LCD_DSI_OBJ_FORCE_INTERNAL
+            bool
+            default n
+            help
+                This will ensure the DSI driver object will always be allocated in internal RAM.
     endif # SOC_MIPI_DSI_SUPPORTED
+
+    config LCD_ENABLE_DEBUG_LOG
+        bool "Force enable debug log"
+        default n
+        help
+            If enabled, LCD driver component will:
+            1. ignore the global logging settings
+            2. compile all log messages into the binary
+            3. set the runtime log level to VERBOSE
+            Please enable this option by caution, as it will increase the binary size.
 endmenu

components/esp_lcd/dsi/esp_lcd_mipi_dsi_bus.c

@@ -1,19 +1,12 @@
 /*
- * SPDX-FileCopyrightText: 2023-2024 Espressif Systems (Shanghai) CO LTD
+ * SPDX-FileCopyrightText: 2023-2025 Espressif Systems (Shanghai) CO LTD
  *
  * SPDX-License-Identifier: Apache-2.0
  */
-#include "freertos/FreeRTOS.h"
-#include "freertos/task.h"
-#include "soc/soc_caps.h"
-#include "esp_check.h"
 #include "esp_lcd_mipi_dsi.h"
 #include "esp_clk_tree.h"
-#include "esp_private/esp_clk_tree_common.h"
 #include "mipi_dsi_priv.h"
 
-static const char *TAG = "lcd.dsi.bus";
-
 #define MIPI_DSI_DEFAULT_TIMEOUT_CLOCK_FREQ_MHZ 10
 // TxClkEsc frequency must be configured between 2 and 20 MHz
 #define MIPI_DSI_DEFAULT_ESCAPE_CLOCK_FREQ_MHZ  18
@@ -38,25 +31,31 @@ esp_err_t esp_lcd_new_dsi_bus(const esp_lcd_dsi_bus_config_t *bus_config, esp_lc
     dsi_bus->bus_id = bus_id;
 
     // Enable the APB clock for accessing the DSI host and bridge registers
-    DSI_RCC_ATOMIC() {
+    PERIPH_RCC_ATOMIC() {
         mipi_dsi_ll_enable_bus_clock(bus_id, true);
         mipi_dsi_ll_reset_register(bus_id);
     }
 
     // if the clock source is not assigned, fallback to the default clock source
-    mipi_dsi_phy_clock_source_t phy_clk_src = bus_config->phy_clk_src;
+    mipi_dsi_phy_pllref_clock_source_t phy_clk_src = bus_config->phy_clk_src;
     if (phy_clk_src == 0) {
-        phy_clk_src = MIPI_DSI_PHY_CLK_SRC_DEFAULT;
+#if SOC_IS(ESP32P4) && HAL_CONFIG(CHIP_SUPPORT_MIN_REV) < 300
+        phy_clk_src = MIPI_DSI_PHY_PLLREF_CLK_SRC_DEFAULT_LEGACY;
+#else
+        phy_clk_src = MIPI_DSI_PHY_PLLREF_CLK_SRC_DEFAULT;
+#endif
     }
     ESP_GOTO_ON_ERROR(esp_clk_tree_enable_src((soc_module_clk_t)phy_clk_src, true), err, TAG, "clock source enable failed");
     // enable the clock source for DSI PHY
-    DSI_CLOCK_SRC_ATOMIC() {
-        // set clock source for DSI PHY
-        mipi_dsi_ll_set_phy_clock_source(bus_id, phy_clk_src);
+    PERIPH_RCC_ATOMIC() {
+        // set the DSI PHY configuration clock
         // the configuration clock is used for all modes except the shutdown mode
+        mipi_dsi_ll_set_phy_config_clock_source(bus_id, MIPI_DSI_PHY_CFG_CLK_SRC_DEFAULT);
         mipi_dsi_ll_enable_phy_config_clock(bus_id, true);
-        // enable the clock for generating the serial clock
-        mipi_dsi_ll_enable_phy_reference_clock(bus_id, true);
+        // set the DSI PHY PLL reference clock
+        mipi_dsi_ll_set_phy_pllref_clock_source(bus_id, phy_clk_src);
+        mipi_dsi_ll_set_phy_pll_ref_clock_div(bus_id, 1); // no division
+        mipi_dsi_ll_enable_phy_pllref_clock(bus_id, true);
     }
 
 #if CONFIG_PM_ENABLE
@@ -135,12 +134,12 @@ esp_err_t esp_lcd_del_dsi_bus(esp_lcd_dsi_bus_handle_t bus)
     ESP_RETURN_ON_FALSE(bus, ESP_ERR_INVALID_ARG, TAG, "invalid argument");
     int bus_id = bus->bus_id;
     // disable the clock source for DSI PHY
-    DSI_CLOCK_SRC_ATOMIC() {
-        mipi_dsi_ll_enable_phy_reference_clock(bus_id, false);
+    PERIPH_RCC_ATOMIC() {
+        mipi_dsi_ll_enable_phy_pllref_clock(bus_id, false);
         mipi_dsi_ll_enable_phy_config_clock(bus_id, false);
     }
     // disable the APB clock for accessing the DSI peripheral registers
-    DSI_RCC_ATOMIC() {
+    PERIPH_RCC_ATOMIC() {
         mipi_dsi_ll_enable_bus_clock(bus_id, false);
     }
 #if CONFIG_PM_ENABLE
@@ -152,3 +151,11 @@ esp_err_t esp_lcd_del_dsi_bus(esp_lcd_dsi_bus_handle_t bus)
     free(bus);
     return ESP_OK;
 }
+
+#if CONFIG_LCD_ENABLE_DEBUG_LOG
+__attribute__((constructor))
+static void mipi_dsi_override_default_log_level(void)
+{
+    esp_log_level_set(TAG, ESP_LOG_VERBOSE);
+}
+#endif

components/esp_lcd/dsi/esp_lcd_panel_dpi.c

@@ -4,11 +4,6 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 #include <sys/param.h>
-#include "freertos/FreeRTOS.h"
-#include "freertos/task.h"
-#include "freertos/semphr.h"
-#include "soc/soc_caps.h"
-#include "esp_check.h"
 #include "esp_lcd_panel_interface.h"
 #include "esp_lcd_mipi_dsi.h"
 #include "esp_clk_tree.h"
@@ -17,13 +12,8 @@
 #include "esp_async_fbcpy.h"
 #include "esp_memory_utils.h"
 #include "esp_private/dw_gdma.h"
-#include "esp_private/esp_clk_tree_common.h"
-#include "hal/cache_hal.h"
-#include "hal/cache_ll.h"
 #include "hal/color_hal.h"
 
-static const char *TAG = "lcd.dsi.dpi";
-
 typedef struct esp_lcd_dpi_panel_t esp_lcd_dpi_panel_t;
 
 static esp_err_t dpi_panel_del(esp_lcd_panel_t *panel);
@@ -77,8 +67,7 @@ static bool async_fbcpy_done_cb(esp_async_fbcpy_handle_t mcp, esp_async_fbcpy_ev
     return need_yield;
 }
 
-IRAM_ATTR
-static bool dma_trans_done_cb(dw_gdma_channel_handle_t chan, const dw_gdma_trans_done_event_data_t *event_data, void *user_data)
+bool mipi_dsi_dma_trans_done_cb(dw_gdma_channel_handle_t chan, const dw_gdma_trans_done_event_data_t *event_data, void *user_data)
 {
     bool yield_needed = false;
     esp_lcd_dpi_panel_t *dpi_panel = (esp_lcd_dpi_panel_t *)user_data;
@@ -152,7 +141,7 @@ static esp_err_t dpi_panel_create_dma_link(esp_lcd_dpi_panel_t *dpi_panel)
 
     // register DMA ISR callbacks
     dw_gdma_event_callbacks_t dsi_dma_cbs = {
-        .on_full_trans_done = dma_trans_done_cb,
+        .on_full_trans_done = mipi_dsi_dma_trans_done_cb,
     };
     ESP_RETURN_ON_ERROR(dw_gdma_channel_register_event_callbacks(dma_chan, &dsi_dma_cbs, dpi_panel), TAG, "register DMA callbacks failed");
 
@@ -177,28 +166,42 @@ esp_err_t esp_lcd_new_panel_dpi(esp_lcd_dsi_bus_handle_t bus, const esp_lcd_dpi_
     }
     ESP_RETURN_ON_FALSE(num_fbs <= DPI_PANEL_MAX_FB_NUM, ESP_ERR_INVALID_ARG, TAG, "num_fbs not within [1,%d]", DPI_PANEL_MAX_FB_NUM);
 
-    size_t bits_per_pixel = 0;
-    switch (panel_config->pixel_format) {
-    case LCD_COLOR_PIXEL_FORMAT_RGB565:
-        bits_per_pixel = 16;
-        break;
-    case LCD_COLOR_PIXEL_FORMAT_RGB666:
-        // RGB data in the memory must be constructed in 6-6-6 (18 bits) for each pixel
-        bits_per_pixel = 18;
-        break;
-    case LCD_COLOR_PIXEL_FORMAT_RGB888:
-        bits_per_pixel = 24;
-        break;
-    }
-    lcd_color_format_t in_color_format = COLOR_TYPE_ID(COLOR_SPACE_RGB, panel_config->pixel_format);
-    // if user sets the in_color_format, it can override the pixel format setting
+    // by default, use RGB888 as the input color format
+    lcd_color_format_t in_color_format = LCD_COLOR_FMT_RGB888;
+    size_t bits_per_pixel = 24;
+    // the deprecated way to set the pixel format
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
+    bool has_pixel_fmt = panel_config->pixel_format != 0;
+    bool has_in_fmt = panel_config->in_color_format != 0;
+    ESP_RETURN_ON_FALSE(has_pixel_fmt ^ has_in_fmt, ESP_ERR_INVALID_ARG, TAG,
+                        "must set exactly one of pixel_format or in_color_format");
+    if (panel_config->pixel_format) {
+        switch (panel_config->pixel_format) {
+        case LCD_COLOR_PIXEL_FORMAT_RGB565:
+            bits_per_pixel = 16;
+            break;
+        case LCD_COLOR_PIXEL_FORMAT_RGB666:
+            // RGB data in the memory must be constructed in 6-6-6 (18 bits) for each pixel
+            bits_per_pixel = 18;
+            break;
+        case LCD_COLOR_PIXEL_FORMAT_RGB888:
+            bits_per_pixel = 24;
+            break;
+        }
+        in_color_format = COLOR_TYPE_ID(COLOR_SPACE_RGB, panel_config->pixel_format);
+    }
+#pragma GCC diagnostic pop
+    // the recommended way to set the input color format
     if (panel_config->in_color_format) {
+        in_color_format = panel_config->in_color_format;
+        // if user sets the in_color_format, it can override the pixel format setting
         color_space_pixel_format_t in_color_id = {
-            .color_type_id = panel_config->in_color_format,
+            .color_type_id = in_color_format,
         };
         bits_per_pixel = color_hal_pixel_format_get_bit_depth(in_color_id);
-        in_color_format = panel_config->in_color_format;
     }
+    // by default, out_color_format is the same as in_color_format (i.e. no color format conversion)
     lcd_color_format_t out_color_format = in_color_format;
     if (panel_config->out_color_format) {
         out_color_format = panel_config->out_color_format;
@@ -218,20 +221,16 @@ esp_err_t esp_lcd_new_panel_dpi(esp_lcd_dsi_bus_handle_t bus, const esp_lcd_dpi_
     dpi_panel->num_fbs = num_fbs;
 
     // allocate frame buffer from PSRAM
-    uint32_t cache_line_size = cache_hal_get_cache_line_size(CACHE_LL_LEVEL_EXT_MEM, CACHE_TYPE_DATA);
-    // DMA doesn't have requirement on the buffer alignment, but the cache does
-    uint32_t alignment = cache_line_size;
     size_t fb_size = panel_config->video_timing.h_size * panel_config->video_timing.v_size * bits_per_pixel / 8;
-    uint8_t *frame_buffer = NULL;
     for (int i = 0; i < num_fbs; i++) {
-        frame_buffer = heap_caps_aligned_calloc(alignment, 1, fb_size, MALLOC_CAP_SPIRAM | MALLOC_CAP_8BIT);
+        uint8_t *frame_buffer = heap_caps_calloc(1, fb_size, MALLOC_CAP_SPIRAM | MALLOC_CAP_8BIT | MALLOC_CAP_DMA);
         ESP_GOTO_ON_FALSE(frame_buffer, ESP_ERR_NO_MEM, err, TAG, "no memory for frame buffer");
         dpi_panel->fbs[i] = frame_buffer;
         ESP_LOGD(TAG, "fb[%d] @%p", i, frame_buffer);
         // preset the frame buffer with black color
-        // the frame buffer address alignment is ensured by `heap_caps_aligned_calloc`
+        // the frame buffer address alignment is ensured by `heap_caps_calloc`
         // while the value of the fb_size may not be aligned to the cache line size
-        // but that's not a problem because the `heap_caps_aligned_calloc` internally allocated a buffer whose size is aligned up to the cache line size
+        // but that's not a problem because the `heap_caps_calloc` internally allocated a buffer whose size is aligned up to the cache line size
         ESP_GOTO_ON_ERROR(esp_cache_msync(frame_buffer, fb_size, ESP_CACHE_MSYNC_FLAG_DIR_C2M | ESP_CACHE_MSYNC_FLAG_UNALIGNED),
                           err, TAG, "cache write back failed");
     }
@@ -264,7 +263,7 @@ esp_err_t esp_lcd_new_panel_dpi(esp_lcd_dsi_bus_handle_t bus, const esp_lcd_dpi_
     uint32_t dpi_div = mipi_dsi_hal_host_dpi_calculate_divider(hal, dpi_clk_src_freq_hz / 1000 / 1000, panel_config->dpi_clock_freq_mhz);
     ESP_GOTO_ON_ERROR(esp_clk_tree_enable_src((soc_module_clk_t)dpi_clk_src, true), err, TAG, "clock source enable failed");
     // set the clock source, set the divider, and enable the dpi clock
-    DSI_CLOCK_SRC_ATOMIC() {
+    PERIPH_RCC_ATOMIC() {
         mipi_dsi_ll_set_dpi_clock_source(bus_id, dpi_clk_src);
         mipi_dsi_ll_set_dpi_clock_div(bus_id, dpi_div);
         mipi_dsi_ll_enable_dpi_clock(bus_id, true);
@@ -283,7 +282,7 @@ esp_err_t esp_lcd_new_panel_dpi(esp_lcd_dsi_bus_handle_t bus, const esp_lcd_dpi_
     ESP_GOTO_ON_ERROR(dpi_panel_create_dma_link(dpi_panel), err, TAG, "initialize DMA link failed");
 
     mipi_dsi_host_ll_dpi_set_vcid(hal->host, panel_config->virtual_channel);
-    mipi_dsi_hal_host_dpi_set_color_coding(hal, out_color_format, 0);
+    mipi_dsi_host_ll_dpi_set_color_coding(hal->host, out_color_format, 0);
     // these signals define how the DPI interface interacts with the controller
     mipi_dsi_host_ll_dpi_set_timing_polarity(hal->host, false, false, false, false, false);
 
@@ -321,8 +320,9 @@ esp_err_t esp_lcd_new_panel_dpi(esp_lcd_dsi_bus_handle_t bus, const esp_lcd_dpi_
                                               panel_config->video_timing.vsync_front_porch);
     mipi_dsi_brg_ll_set_num_pixel_bits(hal->bridge, panel_config->video_timing.h_size * panel_config->video_timing.v_size * bits_per_pixel);
     mipi_dsi_brg_ll_set_underrun_discard_count(hal->bridge, panel_config->video_timing.h_size);
-    // set input color space
-    mipi_dsi_brg_ll_set_input_color_space(hal->bridge, COLOR_SPACE_TYPE(in_color_format));
+    // set the in/out color formats in the DSI bridge
+    mipi_dsi_brg_ll_set_input_color_format(hal->bridge, in_color_format);
+    mipi_dsi_brg_ll_set_output_color_format(hal->bridge, out_color_format, 0);
     // use the DW_GDMA as the flow controller
     mipi_dsi_brg_ll_set_flow_controller(hal->bridge, MIPI_DSI_LL_FLOW_CONTROLLER_DMA);
     mipi_dsi_brg_ll_set_multi_block_number(hal->bridge, DPI_PANEL_MIN_DMA_NODES_PER_LINK);
@@ -352,7 +352,7 @@ static esp_err_t dpi_panel_del(esp_lcd_panel_t *panel)
     int bus_id = bus->bus_id;
     mipi_dsi_hal_context_t *hal = &bus->hal;
     // disable the DPI clock
-    DSI_CLOCK_SRC_ATOMIC() {
+    PERIPH_RCC_ATOMIC() {
         mipi_dsi_ll_enable_dpi_clock(bus_id, false);
     }
     // disable the DSI bridge
@@ -574,6 +574,7 @@ esp_err_t esp_lcd_dpi_panel_set_color_conversion(esp_lcd_panel_handle_t panel, c
     if (dpi_panel->in_color_format == COLOR_TYPE_ID(COLOR_SPACE_YUV, COLOR_PIXEL_YUV422)
             && COLOR_SPACE_TYPE(dpi_panel->out_color_format) == LCD_COLOR_SPACE_RGB) {
         // YUV422->RGB
+        mipi_dsi_brg_ll_set_input_color_range(hal->bridge, config->in_color_range);
         mipi_dsi_brg_ll_set_yuv_convert_std(hal->bridge, config->spec.yuv.conv_std);
         mipi_dsi_brg_ll_set_yuv422_pack_order(hal->bridge, config->spec.yuv.yuv422.in_pack_order);
     } else {
@@ -611,7 +612,7 @@ esp_err_t esp_lcd_dpi_panel_register_event_callbacks(esp_lcd_panel_handle_t pane
 {
     ESP_RETURN_ON_FALSE(panel && cbs, ESP_ERR_INVALID_ARG, TAG, "invalid argument");
     esp_lcd_dpi_panel_t *dpi_panel = __containerof(panel, esp_lcd_dpi_panel_t, base);
-#if CONFIG_LCD_DSI_ISR_IRAM_SAFE
+#if CONFIG_LCD_DSI_ISR_HANDLER_IN_IRAM
     if (cbs->on_color_trans_done) {
         ESP_RETURN_ON_FALSE(esp_ptr_in_iram(cbs->on_color_trans_done), ESP_ERR_INVALID_ARG, TAG, "on_color_trans_done callback not in IRAM");
     }
@@ -621,7 +622,7 @@ esp_err_t esp_lcd_dpi_panel_register_event_callbacks(esp_lcd_panel_handle_t pane
     if (user_ctx) {
         ESP_RETURN_ON_FALSE(esp_ptr_internal(user_ctx), ESP_ERR_INVALID_ARG, TAG, "user context not in internal RAM");
     }
-#endif // CONFIG_LCD_RGB_ISR_IRAM_SAFE
+#endif // CONFIG_LCD_DSI_ISR_HANDLER_IN_IRAM
     dpi_panel->on_color_trans_done = cbs->on_color_trans_done;
     dpi_panel->on_refresh_done = cbs->on_refresh_done;
     dpi_panel->user_ctx = user_ctx;

components/esp_lcd/dsi/esp_lcd_panel_io_dbi.c

@@ -1,18 +1,12 @@
 /*
- * SPDX-FileCopyrightText: 2023-2024 Espressif Systems (Shanghai) CO LTD
+ * SPDX-FileCopyrightText: 2023-2025 Espressif Systems (Shanghai) CO LTD
  *
  * SPDX-License-Identifier: Apache-2.0
  */
-#include "freertos/FreeRTOS.h"
-#include "freertos/task.h"
-#include "soc/soc_caps.h"
-#include "esp_check.h"
 #include "esp_lcd_panel_io_interface.h"
 #include "esp_lcd_mipi_dsi.h"
 #include "mipi_dsi_priv.h"
 
-static const char *TAG = "lcd.dsi.dbi";
-
 typedef struct esp_lcd_dbi_io_t esp_lcd_dbi_io_t;
 
 struct esp_lcd_dbi_io_t {

components/esp_lcd/dsi/include/esp_lcd_mipi_dsi.h

@@ -23,7 +23,7 @@ extern "C" {
 typedef struct {
     int bus_id;                              /*!< Select which DSI controller, index from 0 */
     uint8_t num_data_lanes;                  /*!< Number of data lanes, if set to 0, the driver will fallback to use maximum number of lanes */
-    mipi_dsi_phy_clock_source_t phy_clk_src; /*!< MIPI DSI PHY clock source */
+    mipi_dsi_phy_pllref_clock_source_t phy_clk_src; /*!< The clock source for the PHY PLL */
     uint32_t lane_bit_rate_mbps;             /*!< Lane bit rate in Mbps */
 } esp_lcd_dsi_bus_config_t;
 
@@ -84,14 +84,15 @@ typedef struct {
     uint8_t virtual_channel;                   /*!< Virtual channel ID, index from 0 */
     mipi_dsi_dpi_clock_source_t dpi_clk_src;   /*!< MIPI DSI DPI clock source */
     uint32_t dpi_clock_freq_mhz;               /*!< DPI clock frequency in MHz */
-    lcd_color_rgb_pixel_format_t pixel_format; /*!< Pixel format that used by the MIPI LCD device */
     lcd_color_format_t in_color_format;        /*!< Format of the input data (color space and pixel format),
                                                     which is the format stored in the frame buffer */
     lcd_color_format_t out_color_format;       /*!< Format of the output data (color space and pixel format),
                                                     which is the format that the panel can accept */
     uint8_t num_fbs;                           /*!< Number of screen-sized frame buffers that allocated by the driver
                                                     By default (set to either 0 or 1) only one frame buffer will be created */
     esp_lcd_video_timing_t video_timing;       /*!< Video timing */
+    /** @deprecated Duplicate of in_color_format; use in_color_format instead. */
+    lcd_color_rgb_pixel_format_t pixel_format __attribute__((deprecated("pixel_format is deprecated, use in_color_format instead"))); /*!< Pixel format that used by the MIPI LCD device */
     /// Extra configuration flags for MIPI DSI DPI panel
     struct extra_dpi_panel_flags {
         uint32_t use_dma2d: 1; /*!< Use DMA2D to copy user buffer to the frame buffer when necessary */