Auto-configure display on Feather RP2350

This should be considered an RFC. Some bits should probably be
moved to common code & tidied up.

If connected to a HDMI monitor, an eeprom will be on the i2c bus
with address 0x50.

When it's found, configure the display to 320x240x16 (default), or to
user settings. Invalid user settings cause a safe mode with a misleading
error: "Heap allocation when VM not running." This is because
common_hal_picodvi_framebuffer_construct throws an exception for invalid
parameters (width, height, and color depth), but the circuitpy VM is not
running.

With the default framebuffer configuration, about 256KiB is left for the
CircuitPython VM.

When a display is configured (whether picodvi or not), board.DISPLAY
exits and can be retrieved. When there's no display (including after
`release_displays()`), accessing `board.DISPLAY` raises an AttributeError.
This behavior should maybe adapted everywhere, but I'm not sure how
much flash size it takes.

Author: jepler

ports/raspberrypi/Makefile

@@ -556,6 +556,7 @@ ifeq ($(CIRCUITPY_PICODVI),1)
 SRC_C += \
 	bindings/picodvi/__init__.c \
 	bindings/picodvi/Framebuffer.c \
+	common-hal/picodvi/__init__.c \
 	common-hal/picodvi/Framebuffer_$(CHIP_VARIANT).c \
 
 ifeq ($(CHIP_VARIANT),RP2040)

ports/raspberrypi/boards/adafruit_feather_rp2350/board.c

@@ -4,6 +4,28 @@
 //
 // SPDX-License-Identifier: MIT
 
+#include "py/obj.h"
 #include "supervisor/board.h"
 
+#include "shared-module/displayio/__init__.h"
+#include "common-hal/picodvi/__init__.h"
+
 // Use the MP_WEAK supervisor/shared/board.c versions of routines not defined here.
+
+
+extern void mp_module_board_attr(mp_obj_t self_in, qstr attr, mp_obj_t *dest);
+
+void mp_module_board_attr(mp_obj_t self_in, qstr attr, mp_obj_t *dest) {
+    if (attr == MP_QSTR_DISPLAY && dest[0] == MP_OBJ_NULL) {
+        mp_obj_base_t *first_display = &displays[0].display_base;
+        if (first_display->type != &mp_type_NoneType && first_display->type != NULL) {
+            dest[0] = MP_OBJ_FROM_PTR(first_display);
+        }
+    }
+}
+
+MP_REGISTER_MODULE_DELEGATION(board_module, mp_module_board_attr);
+
+void board_init(void) {
+    picodvi_autoconstruct();
+}

ports/raspberrypi/boards/adafruit_feather_rp2350/mpconfigboard.h

@@ -20,3 +20,15 @@
 #define DEFAULT_UART_BUS_TX (&pin_GPIO0)
 
 #define CIRCUITPY_PSRAM_CHIP_SELECT (&pin_GPIO8)
+
+#define DEFAULT_DVI_BUS_CLK_DN (&pin_GPIO15)
+#define DEFAULT_DVI_BUS_CLK_DP (&pin_GPIO14)
+#define DEFAULT_DVI_BUS_RED_DN (&pin_GPIO19)
+#define DEFAULT_DVI_BUS_RED_DP (&pin_GPIO18)
+#define DEFAULT_DVI_BUS_GREEN_DN (&pin_GPIO17)
+#define DEFAULT_DVI_BUS_GREEN_DP (&pin_GPIO16)
+#define DEFAULT_DVI_BUS_BLUE_DN (&pin_GPIO13)
+#define DEFAULT_DVI_BUS_BLUE_DP (&pin_GPIO12)
+
+// delegate board.DISPLAY attribute
+#define MICROPY_MODULE_ATTR_DELEGATION (1)

ports/raspberrypi/common-hal/picodvi/__init__.c

@@ -0,0 +1,71 @@
+// This file is part of the CircuitPython project: https://circuitpython.org
+//
+// SPDX-FileCopyrightText: Copyright (c) 2025 Jeff Epler for Adafruit Industries
+//
+// SPDX-License-Identifier: MIT
+
+#include "common-hal/picodvi/__init__.h"
+#include "common-hal/picodvi/Framebuffer.h"
+#include "bindings/picodvi/Framebuffer.h"
+#include "shared-bindings/busio/I2C.h"
+#include "shared-bindings/board/__init__.h"
+#include "shared-module/displayio/__init__.h"
+#include "shared-module/os/__init__.h"
+#include "supervisor/shared/safe_mode.h"
+#include "py/gc.h"
+#include "py/runtime.h"
+#include "supervisor/port_heap.h"
+
+void picodvi_autoconstruct(void) {
+    if (get_safe_mode() != SAFE_MODE_NONE) {
+        return;
+    }
+    #if defined(DEFAULT_DVI_BUS_CLK_DP)
+    // check if address 0x50 is live on the I2C bus -- return if not
+    busio_i2c_obj_t *i2c = common_hal_board_create_i2c(0);
+    if (!i2c) {
+        return;
+    }
+    if (!common_hal_busio_i2c_try_lock(i2c)) {
+        return;
+    }
+    bool probed = common_hal_busio_i2c_probe(i2c, 0x50);
+    common_hal_busio_i2c_unlock(i2c);
+    if (!probed) {
+        return;
+    }
+
+    mp_int_t width = 320;
+    mp_int_t height = 240;
+    mp_int_t color_depth = 16;
+
+    // TODO: User configuration can cause safe mode errors without a self-explanatory message.
+    common_hal_os_getenv_int("CIRCUITPY_DISPLAY_WIDTH", &width);
+    common_hal_os_getenv_int("CIRCUITPY_DISPLAY_HEIGHT", &height);
+    common_hal_os_getenv_int("CIRCUITPY_DISPLAY_COLOR_DEPTH", &color_depth);
+
+    // construct framebuffer and display
+
+    picodvi_framebuffer_obj_t *fb = &allocate_display_bus_or_raise()->picodvi;
+    fb->base.type = &picodvi_framebuffer_type;
+    common_hal_picodvi_framebuffer_construct(fb,
+        width, height,
+        DEFAULT_DVI_BUS_CLK_DP,
+        DEFAULT_DVI_BUS_CLK_DN,
+        DEFAULT_DVI_BUS_RED_DP,
+        DEFAULT_DVI_BUS_RED_DN,
+        DEFAULT_DVI_BUS_GREEN_DP,
+        DEFAULT_DVI_BUS_GREEN_DN,
+        DEFAULT_DVI_BUS_BLUE_DP,
+        DEFAULT_DVI_BUS_BLUE_DN,
+        color_depth);
+
+    framebufferio_framebufferdisplay_obj_t *display = &allocate_display()->framebuffer_display;
+    display->base.type = &framebufferio_framebufferdisplay_type;
+    common_hal_framebufferio_framebufferdisplay_construct(
+        display,
+        MP_OBJ_FROM_PTR(fb),
+        0,
+        true);
+    #endif
+}

ports/raspberrypi/common-hal/picodvi/__init__.h

@@ -0,0 +1,9 @@
+// This file is part of the CircuitPython project: https://circuitpython.org
+//
+// SPDX-FileCopyrightText: Copyright (c) 2025 Jeff Epler for Adafruit Industries
+//
+// SPDX-License-Identifier: MIT
+
+#pragma once
+
+extern void picodvi_autoconstruct(void);