async_spi: report Zephyr transfer errors, wait without background tasks

The driver's result reaches the await as an exception. cancel() and
deinit() wait for the transfer without running background tasks, since
they may run from a finalizer during GC. async_spi needs asyncio, not
only async/await, so raspberrypi enables it with MICROPY_PY_ASYNCIO.

Author: lynt-smitka

ports/raspberrypi/mpconfigport.mk

@@ -7,7 +7,7 @@ CIRCUITPY_WIFI_RADIO_SETTABLE_MAC_ADDRESS = 0
 
 CIRCUITPY_RP2PIO ?= 1
 CIRCUITPY_BUSIO_SPI_ASYNC ?= 1
-CIRCUITPY_ASYNC_SPI ?= $(call enable-if-all,$(MICROPY_PY_ASYNC_AWAIT) $(CIRCUITPY_BUSIO_SPI) $(CIRCUITPY_BUSIO_SPI_ASYNC))
+CIRCUITPY_ASYNC_SPI ?= $(call enable-if-all,$(MICROPY_PY_ASYNCIO) $(CIRCUITPY_BUSIO_SPI) $(CIRCUITPY_BUSIO_SPI_ASYNC))
 # The 24 KB stack has room for a larger display refresh buffer.
 CIRCUITPY_DISPLAY_AREA_BUFFER_SIZE ?= 2048
 CIRCUITPY_NEOPIXEL_WRITE ?= $(CIRCUITPY_RP2PIO)

ports/zephyr-cp/common-hal/async_spi/SPI.c

@@ -28,8 +28,8 @@ static void apply_config(async_spi_spi_obj_t *self, uint32_t frequency, uint16_t
 
 static void transfer_done(const struct device *dev, int result, void *userdata) {
     ARG_UNUSED(dev);
-    ARG_UNUSED(result);
     async_spi_spi_obj_t *self = userdata;
+    self->result = result;
     CIRCUITPY_ASYNC_FLAG_SET(self->done);
     // A configure() that waited for this transfer.
     if (self->idle_done != NULL) {
@@ -40,13 +40,14 @@ static void transfer_done(const struct device *dev, int result, void *userdata)
     port_wake_main_task_from_isr();
 }
 
-// Zephyr cannot stop a transfer, so this waits for it; deinit() waits too. Does not allocate.
+// Zephyr cannot stop a transfer, so cancel and deinit wait for it. No background tasks: this
+// also runs from a finalizer during GC.
 static void wait_done(async_spi_spi_obj_t *self) {
     if (self->done == NULL) {
         return;
     }
     while (!CIRCUITPY_ASYNC_FLAG_IS_SET(self->done)) {
-        RUN_BACKGROUND_TASKS;
+        port_task_sleep_ms(1);
     }
     self->done = NULL;
 }
@@ -154,6 +155,7 @@ static void start(async_spi_spi_obj_t *self, const uint8_t *data_out, uint8_t *d
     wait_done(self);
     CIRCUITPY_ASYNC_FLAG_INIT(done);
     self->done = done;
+    self->result = 0;
     if (len == 0) {
         CIRCUITPY_ASYNC_FLAG_SET(done);
         return;
@@ -203,14 +205,21 @@ void common_hal_async_spi_spi_write_readinto_start(async_spi_spi_obj_t *self,
     start(self, data_out, data_in, len, done);
 }
 
+// Called once done is set.
 mp_obj_t common_hal_async_spi_spi_transfer_end(void *context, circuitpy_async_flag_t *done) {
     async_spi_spi_obj_t *self = context;
     if (self->done == done) {
-        wait_done(self);
+        self->done = NULL;
+        if (self->result != 0) {
+            raise_zephyr_error(self->result);
+        }
     }
     return mp_const_none;
 }
 
 void common_hal_async_spi_spi_transfer_cancel(void *context, circuitpy_async_flag_t *done) {
-    common_hal_async_spi_spi_transfer_end(context, done);
+    async_spi_spi_obj_t *self = context;
+    if (self->done == done) {
+        wait_done(self);
+    }
 }

ports/zephyr-cp/common-hal/async_spi/SPI.h

@@ -23,6 +23,7 @@ typedef struct {
     const mcu_pin_obj_t *mosi;
     const mcu_pin_obj_t *miso;
     circuitpy_async_flag_t *done;       // of the running transfer, NULL when none
+    int result;                         // of the last transfer, from the driver
     struct spi_buf tx_buf;              // the running transfer's buffers
     struct spi_buf rx_buf;
     struct spi_buf_set tx;