rp2/machine_spi: Detect RX overrun when using DMA transfers.

Fixes bug where SPI can freeze if another DMA channel is
tranferring to/from PSRAM.

Signed-off-by: Dryw Wade <dryw.wade@sparkfun.com>

Author: sfe-SparkFro

ports/rp2/machine_spi.c

@@ -273,6 +273,7 @@ static void machine_spi_transfer(mp_obj_base_t *self_in, size_t len, const uint8
     bool use_dma = chan_rx >= 0 && chan_tx >= 0;
     // note src is guaranteed to be non-NULL
     bool write_only = dest == NULL;
+    bool success = true;
 
     if (use_dma) {
         uint8_t dev_null;
@@ -297,8 +298,16 @@ static void machine_spi_transfer(mp_obj_base_t *self_in, size_t len, const uint8
             false);
 
         dma_start_channel_mask((1u << chan_rx) | (1u << chan_tx));
-        dma_channel_wait_for_finish_blocking(chan_rx);
         dma_channel_wait_for_finish_blocking(chan_tx);
+
+        // Fix for #18471. Wait for SPI to finish then check for RX overrun
+        while (spi_is_busy(self->spi_inst) || spi_is_readable(self->spi_inst)) {
+        }
+        if (spi_get_const_hw(self->spi_inst)->ris & SPI_SSPRIS_RORRIS_BITS) {
+            // RX overrun occurred, RX DMA channel needs to be manually aborted
+            success = false;
+            dma_channel_abort(chan_rx);
+        }
     }
 
     // If we have claimed only one channel successfully, we should release immediately
@@ -317,6 +326,11 @@ static void machine_spi_transfer(mp_obj_base_t *self_in, size_t len, const uint8
             spi_write_read_blocking(self->spi_inst, src, dest, len);
         }
     }
+
+    // Raise OSError if something went wrong
+    if (!success) {
+        mp_raise_OSError(MP_EIO);
+    }
 }
 
 // Buffer protocol implementation for SPI.