rp2/rp2_dma: Properly close DMA channels.

Clears the control registers and aborts the closed channel upon a call to
`.close()` and `.__del__()` (GC collect).

Fixes issue micropython#18446.

Signed-off-by: Dryw Wade <[email protected]>

Author: sfe-SparkFro

ports/rp2/rp2_dma.c

@@ -427,6 +427,14 @@ static mp_obj_t rp2_dma_close(mp_obj_t self_in) {
     uint8_t channel = self->channel;
 
     if (channel != CHANNEL_CLOSED) {
+        // Reset this channel's registers to their default values (zeros).
+        dma_channel_config config = { .ctrl = 0 };
+        dma_channel_configure(channel, &config, NULL, NULL, 0, false);
+
+        // Abort this channel. Must be done after clearing EN bit in control
+        // register due to errata RP2350-E5.
+        dma_channel_abort(channel);
+
         // Clean up interrupt handler to ensure garbage collection
         mp_irq_obj_t *irq = MP_STATE_PORT(rp2_dma_irq_obj[channel]);
         MP_STATE_PORT(rp2_dma_irq_obj[channel]) = MP_OBJ_NULL;