rp2/machine_uart: Fix unintended UART buffer allocation on init().

The buffer was be reset on every call to uart.init().  If no sizes were
given, the buffer was set to the default size 256.  That made problems e.g.
with PPP.

This commit fixes it, keeping the buffer size if not deliberately changed
and allocating new buffers only if the size was changed.

Signed-off-by: robert-hh <robert@hammelrath.com>

Author: robert-hh

ports/rp2/machine_uart.c

@@ -116,8 +116,10 @@ typedef struct _machine_uart_obj_t {
     uint16_t timeout_char;  // timeout waiting between chars (in ms)
     uint8_t invert;
     uint8_t flow;
+    uint16_t rxbuf_len;
     ringbuf_t read_buffer;
     mutex_t *read_mutex;
+    uint16_t txbuf_len;
     ringbuf_t write_buffer;
     mutex_t *write_mutex;
     uint16_t mp_irq_trigger;   // user IRQ trigger mask
@@ -128,10 +130,10 @@ typedef struct _machine_uart_obj_t {
 static machine_uart_obj_t machine_uart_obj[] = {
     {{&machine_uart_type}, uart0, 0, 0, DEFAULT_UART_BITS, UART_PARITY_NONE, DEFAULT_UART_STOP,
      MICROPY_HW_UART0_TX, MICROPY_HW_UART0_RX, MICROPY_HW_UART0_CTS, MICROPY_HW_UART0_RTS,
-     0, 0, 0, 0, {NULL, 1, 0, 0}, &read_mutex_0, {NULL, 1, 0, 0}, &write_mutex_0, 0, 0, NULL},
+     0, 0, 0, 0, 0, {NULL, 1, 0, 0}, &read_mutex_0, 0, {NULL, 1, 0, 0}, &write_mutex_0, 0, 0, NULL},
     {{&machine_uart_type}, uart1, 1, 0, DEFAULT_UART_BITS, UART_PARITY_NONE, DEFAULT_UART_STOP,
      MICROPY_HW_UART1_TX, MICROPY_HW_UART1_RX, MICROPY_HW_UART1_CTS, MICROPY_HW_UART1_RTS,
-     0, 0, 0, 0, {NULL, 1, 0, 0}, &read_mutex_1, {NULL, 1, 0, 0}, &write_mutex_1},
+     0, 0, 0, 0, 0, {NULL, 1, 0, 0}, &read_mutex_1, 0, {NULL, 1, 0, 0}, &write_mutex_1, 0, 0, NULL},
 };
 
 static const char *_parity_name[] = {"None", "0", "1"};
@@ -252,7 +254,7 @@ static void mp_machine_uart_print(const mp_print_t *print, mp_obj_t self_in, mp_
     mp_printf(print, "UART(%u, baudrate=%u, bits=%u, parity=%s, stop=%u, tx=%d, rx=%d, "
         "txbuf=%d, rxbuf=%d, timeout=%u, timeout_char=%u, invert=%s, irq=%d)",
         self->uart_id, self->baudrate, self->bits, _parity_name[self->parity],
-        self->stop, self->tx, self->rx, self->write_buffer.size - 1, self->read_buffer.size - 1,
+        self->stop, self->tx, self->rx, self->txbuf_len, self->rxbuf_len,
         self->timeout, self->timeout_char, _invert_name[self->invert], self->mp_irq_trigger);
 }
 
@@ -365,25 +367,33 @@ static void mp_machine_uart_init_helper(machine_uart_obj_t *self, size_t n_args,
     }
 
     // Set the RX buffer size if configured.
-    size_t rxbuf_len = DEFAULT_BUFFER_SIZE;
     if (args[ARG_rxbuf].u_int > 0) {
-        rxbuf_len = args[ARG_rxbuf].u_int;
+        size_t rxbuf_len = args[ARG_rxbuf].u_int;
         if (rxbuf_len < MIN_BUFFER_SIZE) {
             rxbuf_len = MIN_BUFFER_SIZE;
         } else if (rxbuf_len > MAX_BUFFER_SIZE) {
             mp_raise_ValueError(MP_ERROR_TEXT("rxbuf too large"));
         }
+        // Force re-allocting of the buffer if the size changed
+        if (rxbuf_len != self->rxbuf_len) {
+            self->read_buffer.buf = NULL;
+            self->rxbuf_len = rxbuf_len;
+        }
     }
 
     // Set the TX buffer size if configured.
-    size_t txbuf_len = DEFAULT_BUFFER_SIZE;
     if (args[ARG_txbuf].u_int > 0) {
-        txbuf_len = args[ARG_txbuf].u_int;
+        size_t txbuf_len = args[ARG_txbuf].u_int;
         if (txbuf_len < MIN_BUFFER_SIZE) {
             txbuf_len = MIN_BUFFER_SIZE;
         } else if (txbuf_len > MAX_BUFFER_SIZE) {
             mp_raise_ValueError(MP_ERROR_TEXT("txbuf too large"));
         }
+        // Force re-allocting of the buffer if the size changed
+        if (txbuf_len != self->txbuf_len) {
+            self->write_buffer.buf = NULL;
+            self->txbuf_len = txbuf_len;
+        }
     }
 
     // Initialise the UART peripheral if any arguments given, or it was not initialised previously.
@@ -423,11 +433,14 @@ static void mp_machine_uart_init_helper(machine_uart_obj_t *self, size_t n_args,
         uart_set_hw_flow(self->uart, self->flow & UART_HWCONTROL_CTS, self->flow & UART_HWCONTROL_RTS);
 
         // Allocate the RX/TX buffers.
-        ringbuf_alloc(&(self->read_buffer), rxbuf_len + 1);
-        MP_STATE_PORT(rp2_uart_rx_buffer[self->uart_id]) = self->read_buffer.buf;
-
-        ringbuf_alloc(&(self->write_buffer), txbuf_len + 1);
-        MP_STATE_PORT(rp2_uart_tx_buffer[self->uart_id]) = self->write_buffer.buf;
+        if (self->read_buffer.buf == NULL) {
+            ringbuf_alloc(&(self->read_buffer), self->rxbuf_len + 1);
+            MP_STATE_PORT(rp2_uart_rx_buffer[self->uart_id]) = self->read_buffer.buf;
+        }
+        if (self->write_buffer.buf == NULL) {
+            ringbuf_alloc(&(self->write_buffer), self->txbuf_len + 1);
+            MP_STATE_PORT(rp2_uart_tx_buffer[self->uart_id]) = self->write_buffer.buf;
+        }
 
         // Set the irq handler.
         if (self->uart_id == 0) {
@@ -454,6 +467,10 @@ static mp_obj_t mp_machine_uart_make_new(const mp_obj_type_t *type, size_t n_arg
 
     // Get static peripheral object.
     machine_uart_obj_t *self = (machine_uart_obj_t *)&machine_uart_obj[uart_id];
+    self->rxbuf_len = DEFAULT_BUFFER_SIZE;
+    self->read_buffer.buf = NULL;
+    self->txbuf_len = DEFAULT_BUFFER_SIZE;
+    self->write_buffer.buf = NULL;
 
     // Initialise the UART peripheral.
     mp_map_t kw_args;