Add non-DMA SPI support.

This fixes SPI with PSRAM allocated buffers. DMA with SPI2 was
attempted but produced junk output. This manual copy is less than
2x slower than DMA when not interrupted.

Fixes #3339

Author: tannewt

ports/esp32s2/common-hal/busio/SPI.c

@@ -183,9 +183,6 @@ void common_hal_busio_spi_construct(busio_spi_obj_t *self,
 
     // spi_hal_init clears the given hal context so set everything after.
     spi_hal_init(hal, host_id);
-    hal->dmadesc_tx = &self->tx_dma;
-    hal->dmadesc_rx = &self->rx_dma;
-    hal->dmadesc_n = 1;
 
     // We don't use native CS.
     // hal->cs_setup = 0;
@@ -196,7 +193,6 @@ void common_hal_busio_spi_construct(busio_spi_obj_t *self,
     hal->half_duplex = 0;
     // hal->tx_lsbfirst = 0;
     // hal->rx_lsbfirst = 0;
-    hal->dma_enabled = 1;
     hal->no_compensate = 1;
     // Ignore CS bits
 
@@ -315,16 +311,34 @@ bool common_hal_busio_spi_transfer(busio_spi_obj_t *self, const uint8_t *data_ou
     hal->rcv_buffer = NULL;
     // Reset timing_conf in case we've moved since the last time we used it.
     hal->timing_conf = &self->timing_conf;
+    lldesc_t tx_dma __attribute__((aligned(16)));
+    lldesc_t rx_dma __attribute__((aligned(16)));
+    hal->dmadesc_tx = &tx_dma;
+    hal->dmadesc_rx = &rx_dma;
+    hal->dmadesc_n = 1;
+
+    size_t burst_length;
+    // If both of the incoming pointers are DMA capable then use DMA. Otherwise, do
+    // bursts the size of the SPI data buffer without DMA.
+    if ((data_out == NULL || esp_ptr_dma_capable(data_out)) &&
+        (data_in == NULL || esp_ptr_dma_capable(data_out))) {
+        hal->dma_enabled = 1;
+        burst_length = LLDESC_MAX_NUM_PER_DESC;
+    } else {
+        hal->dma_enabled = 0;
+        burst_length = sizeof(hal->hw->data_buf);
+    }
+
     // This rounds up.
-    size_t dma_count = (len + LLDESC_MAX_NUM_PER_DESC - 1) / LLDESC_MAX_NUM_PER_DESC;
-    for (size_t i = 0; i < dma_count; i++) {
-        size_t offset = LLDESC_MAX_NUM_PER_DESC * i;
-        size_t dma_len = len - offset;
-        if (dma_len > LLDESC_MAX_NUM_PER_DESC) {
-            dma_len = LLDESC_MAX_NUM_PER_DESC;
+    size_t burst_count = (len + burst_length - 1) / burst_length;
+    for (size_t i = 0; i < burst_count; i++) {
+        size_t offset = burst_length * i;
+        size_t this_length = len - offset;
+        if (this_length > burst_length) {
+            this_length = burst_length;
         }
-        hal->tx_bitlen = dma_len * self->bits;
-        hal->rx_bitlen = dma_len * self->bits;
+        hal->tx_bitlen = this_length * self->bits;
+        hal->rx_bitlen = this_length * self->bits;
         if (data_out != NULL) {
             hal->send_buffer = (uint8_t*) data_out + offset;
         }
@@ -341,6 +355,9 @@ bool common_hal_busio_spi_transfer(busio_spi_obj_t *self, const uint8_t *data_ou
         }
         spi_hal_fetch_result(hal);
     }
+    hal->dmadesc_tx = NULL;
+    hal->dmadesc_rx = NULL;
+    hal->dmadesc_n = 0;
 
     return true;
 }

ports/esp32s2/common-hal/busio/SPI.h

@@ -44,10 +44,6 @@ typedef struct {
     spi_hal_context_t hal_context;
     spi_hal_timing_conf_t timing_conf;
     intr_handle_t interrupt;
-    // IDF allocates these in DMA accessible memory so they may need to move when
-    // we use external RAM for CircuitPython.
-    lldesc_t tx_dma;
-    lldesc_t rx_dma;
     uint32_t target_frequency;
     int32_t real_frequency;
     uint8_t polarity;