drivers: serial: uart_xlnx_ps: Fix interrupt mode issues

This driver had some issues with interrupt-driven operation, which
manifested by the console breaking when enabling the Zephyr shell on the
kv260_r5 target for example. Fixed the following:

-Ensure device is fully hardware reset during initialization

-Changed poll_out to be more consistent with other drivers, i.e. only
wait for the UART to accept the character, not for it to be fully
transmitted.

-Added implementation for err_check function, as otherwise there was no
way to detect or clear the error interrupts enabled by irq_err_enable.

-Fixed logic for enabling/disabling interrupts. This should only be done
by explicit enable/disable calls, not as part of fifo_fill etc.

-This hardware does not produce interrupts for TX FIFO empty or RX FIFO
threshold when enabling them if the TX FIFO is already empty or RX FIFO
already contains data. When enabling interrupts in these cases, use a
timer to trigger a user callback to match the normal UART API usage,
similar to the xlnx_uartlite driver.

-Other minor cleanups to interrupt-driven functions.

Signed-off-by: Robert Hancock <robert.hancock@calian.com>

Author: robhancocksed

drivers/serial/uart_xlnx_ps.c

@@ -158,6 +158,8 @@ struct uart_xlnx_ps_dev_data_t {
 	uint32_t flowctrl;
 
 #ifdef CONFIG_UART_INTERRUPT_DRIVEN
+	const struct device *dev;
+	struct k_timer timer;
 	uart_irq_callback_user_data_t user_cb;
 	void *user_data;
 #endif
@@ -270,6 +272,25 @@ static void set_baudrate(const struct device *dev, uint32_t baud_rate)
 	}
 }
 
+#ifdef CONFIG_UART_INTERRUPT_DRIVEN
+
+/**
+ * @brief Trigger a UART callback based on a timer.
+ *
+ * @param timer Timer that triggered the callback
+ */
+static void uart_xlnx_ps_soft_isr(struct k_timer *timer)
+{
+	struct uart_xlnx_ps_dev_data_t *data =
+		CONTAINER_OF(timer, struct uart_xlnx_ps_dev_data_t, timer);
+
+	if (data->user_cb) {
+		data->user_cb(data->dev, data->user_data);
+	}
+}
+
+#endif
+
 /**
  * @brief Initialize individual UART port
  *
@@ -290,16 +311,18 @@ static int uart_xlnx_ps_init(const struct device *dev)
 	DEVICE_MMIO_MAP(dev, K_MEM_CACHE_NONE);
 	uintptr_t reg_base = DEVICE_MMIO_GET(dev);
 
-	/* Disable RX/TX before changing any configuration data */
-	xlnx_ps_disable_uart(reg_base);
-
 #ifdef CONFIG_PINCTRL
 	err = pinctrl_apply_state(dev_cfg->pincfg, PINCTRL_STATE_DEFAULT);
 	if (err < 0) {
 		return err;
 	}
 #endif
 
+	/* Set RX/TX reset and disable RX/TX */
+	sys_write32(XUARTPS_CR_STOPBRK | XUARTPS_CR_TX_DIS | XUARTPS_CR_RX_DIS | XUARTPS_CR_TXRST |
+			    XUARTPS_CR_RXRST,
+		    reg_base + XUARTPS_CR_OFFSET);
+
 	/* Set initial character length / start/stop bit / parity configuration */
 	reg_val = sys_read32(reg_base + XUARTPS_MR_OFFSET);
 	reg_val &= (~(XUARTPS_MR_CHARLEN_MASK | XUARTPS_MR_STOPMODE_MASK | XUARTPS_MR_PARITY_MASK));
@@ -316,10 +339,14 @@ static int uart_xlnx_ps_init(const struct device *dev)
 	set_baudrate(dev, dev_cfg->baud_rate);
 
 #ifdef CONFIG_UART_INTERRUPT_DRIVEN
+	struct uart_xlnx_ps_dev_data_t *dev_data = dev->data;
 
 	/* Clear any pending interrupt flags */
 	sys_write32(XUARTPS_IXR_MASK, reg_base + XUARTPS_ISR_OFFSET);
 
+	dev_data->dev = dev;
+	k_timer_init(&dev_data->timer, &uart_xlnx_ps_soft_isr, NULL);
+
 	/* Attach to & unmask the corresponding interrupt vector */
 	dev_cfg->irq_config_func(dev);
 
@@ -354,7 +381,7 @@ static int uart_xlnx_ps_poll_in(const struct device *dev, unsigned char *c)
 /**
  * @brief Output a character in polled mode.
  *
- * Checks if the transmitter is empty. If empty, a character is written to
+ * Checks if the transmitter has available TX FIFO space. If so, a character is written to
  * the data register.
  *
  * If the hardware flow control is enabled then the handshake signal CTS has to
@@ -368,18 +395,54 @@ static int uart_xlnx_ps_poll_in(const struct device *dev, unsigned char *c)
 static void uart_xlnx_ps_poll_out(const struct device *dev, unsigned char c)
 {
 	uintptr_t reg_base = DEVICE_MMIO_GET(dev);
-	uint32_t reg_val;
 
-	/* wait for transmitter to ready to accept a character */
-	do {
-		reg_val = sys_read32(reg_base + XUARTPS_SR_OFFSET);
-	} while ((reg_val & XUARTPS_SR_TXEMPTY) == 0);
+	/* wait for transmitter to be ready to accept a character */
+	while ((sys_read32(reg_base + XUARTPS_SR_OFFSET) & XUARTPS_SR_TXFULL) != 0) {
+	}
 
 	sys_write32((uint32_t)(c & 0xFF), reg_base + XUARTPS_FIFO_OFFSET);
+}
+
+/**
+ * Check for pending TX/TX errors on the port.
+ *
+ * @param dev UART device struct
+ * @return 0 if no errors, UART_ERROR_* flags otherwise
+ */
+static int uart_xlnx_ps_err_check(const struct device *dev)
+{
+	uintptr_t reg_base = DEVICE_MMIO_GET(dev);
+	uint32_t reg_val = sys_read32(reg_base + XUARTPS_ISR_OFFSET);
+	int err = 0;
+
+	if (reg_val & XUARTPS_IXR_RBRK) {
+		err |= UART_BREAK;
+	}
 
-	do {
-		reg_val = sys_read32(reg_base + XUARTPS_SR_OFFSET);
-	} while ((reg_val & XUARTPS_SR_TXEMPTY) == 0);
+	if (reg_val & XUARTPS_IXR_TOVR) {
+		err |= UART_ERROR_OVERRUN;
+	}
+
+	if (reg_val & XUARTPS_IXR_TOUT) {
+		err |= UART_ERROR_NOISE;
+	}
+
+	if (reg_val & XUARTPS_IXR_PARITY) {
+		err |= UART_ERROR_PARITY;
+	}
+
+	if (reg_val & XUARTPS_IXR_FRAMING) {
+		err |= UART_ERROR_FRAMING;
+	}
+
+	if (reg_val & XUARTPS_IXR_RXOVR) {
+		err |= UART_ERROR_OVERRUN;
+	}
+	sys_write32(reg_val & (XUARTPS_IXR_RBRK | XUARTPS_IXR_TOVR | XUARTPS_IXR_TOUT |
+			       XUARTPS_IXR_PARITY | XUARTPS_IXR_FRAMING | XUARTPS_IXR_RXOVR),
+		    reg_base + XUARTPS_ISR_OFFSET);
+
+	return err;
 }
 
 /**
@@ -826,17 +889,14 @@ static int uart_xlnx_ps_config_get(const struct device *dev, struct uart_config
 static int uart_xlnx_ps_fifo_fill(const struct device *dev, const uint8_t *tx_data, int size)
 {
 	uintptr_t reg_base = DEVICE_MMIO_GET(dev);
-	uint32_t data_iter = 0;
+	int count = 0;
 
-	sys_write32(XUARTPS_IXR_TXEMPTY, reg_base + XUARTPS_IDR_OFFSET);
-	while (size--) {
-		while ((sys_read32(reg_base + XUARTPS_SR_OFFSET) & XUARTPS_SR_TXFULL) != 0) {
-		}
-		sys_write32((uint32_t)tx_data[data_iter++], reg_base + XUARTPS_FIFO_OFFSET);
+	while (count < size &&
+	       (sys_read32(reg_base + XUARTPS_SR_OFFSET) & XUARTPS_SR_TXFULL) == 0) {
+		sys_write32((uint32_t)tx_data[count++], reg_base + XUARTPS_FIFO_OFFSET);
 	}
-	sys_write32(XUARTPS_IXR_TXEMPTY, reg_base + XUARTPS_IER_OFFSET);
 
-	return data_iter;
+	return count;
 }
 
 /**
@@ -851,16 +911,14 @@ static int uart_xlnx_ps_fifo_fill(const struct device *dev, const uint8_t *tx_da
 static int uart_xlnx_ps_fifo_read(const struct device *dev, uint8_t *rx_data, const int size)
 {
 	uintptr_t reg_base = DEVICE_MMIO_GET(dev);
-	uint32_t reg_val = sys_read32(reg_base + XUARTPS_SR_OFFSET);
-	int inum = 0;
+	int count = 0;
 
-	while (inum < size && (reg_val & XUARTPS_SR_RXEMPTY) == 0) {
-		rx_data[inum] = (uint8_t)sys_read32(reg_base + XUARTPS_FIFO_OFFSET);
-		inum++;
-		reg_val = sys_read32(reg_base + XUARTPS_SR_OFFSET);
+	while (count < size &&
+	       (sys_read32(reg_base + XUARTPS_SR_OFFSET) & XUARTPS_SR_RXEMPTY) == 0) {
+		rx_data[count++] = (uint8_t)sys_read32(reg_base + XUARTPS_FIFO_OFFSET);
 	}
 
-	return inum;
+	return count;
 }
 
 /**
@@ -870,9 +928,20 @@ static int uart_xlnx_ps_fifo_read(const struct device *dev, uint8_t *rx_data, co
  */
 static void uart_xlnx_ps_irq_tx_enable(const struct device *dev)
 {
+	struct uart_xlnx_ps_dev_data_t *dev_data = dev->data;
 	uintptr_t reg_base = DEVICE_MMIO_GET(dev);
 
 	sys_write32((XUARTPS_IXR_TTRIG | XUARTPS_IXR_TXEMPTY), reg_base + XUARTPS_IER_OFFSET);
+	if ((sys_read32(reg_base + XUARTPS_SR_OFFSET) & (XUARTPS_SR_TTRIG | XUARTPS_SR_TXEMPTY)) !=
+	    0) {
+		/*
+		 * Enabling TX empty interrupts does not cause an interrupt
+		 * if the FIFO is already empty.
+		 * Generate a soft interrupt and have it call the
+		 * callback function in timer isr context.
+		 */
+		k_timer_start(&dev_data->timer, K_NO_WAIT, K_NO_WAIT);
+	}
 }
 
 /**
@@ -918,11 +987,7 @@ static int uart_xlnx_ps_irq_tx_complete(const struct device *dev)
 	uintptr_t reg_base = DEVICE_MMIO_GET(dev);
 	uint32_t reg_val = sys_read32(reg_base + XUARTPS_SR_OFFSET);
 
-	if ((reg_val & XUARTPS_SR_TXEMPTY) == 0) {
-		return 0;
-	} else {
-		return 1;
-	}
+	return (reg_val & XUARTPS_SR_TXEMPTY) != 0;
 }
 
 /**
@@ -932,9 +997,19 @@ static int uart_xlnx_ps_irq_tx_complete(const struct device *dev)
  */
 static void uart_xlnx_ps_irq_rx_enable(const struct device *dev)
 {
+	struct uart_xlnx_ps_dev_data_t *dev_data = dev->data;
 	uintptr_t reg_base = DEVICE_MMIO_GET(dev);
 
 	sys_write32(XUARTPS_IXR_RTRIG, reg_base + XUARTPS_IER_OFFSET);
+	if ((sys_read32(reg_base + XUARTPS_SR_OFFSET) & XUARTPS_SR_RXEMPTY) == 0) {
+		/*
+		 * Enabling RX trigger interrupts does not cause an interrupt
+		 * if the FIFO already contains RX data.
+		 * Generate a soft interrupt and have it call the
+		 * callback function in timer isr context.
+		 */
+		k_timer_start(&dev_data->timer, K_NO_WAIT, K_NO_WAIT);
+	}
 }
 
 /**
@@ -959,14 +1034,9 @@ static void uart_xlnx_ps_irq_rx_disable(const struct device *dev)
 static int uart_xlnx_ps_irq_rx_ready(const struct device *dev)
 {
 	uintptr_t reg_base = DEVICE_MMIO_GET(dev);
-	uint32_t reg_val = sys_read32(reg_base + XUARTPS_ISR_OFFSET);
+	uint32_t reg_val = sys_read32(reg_base + XUARTPS_SR_OFFSET);
 
-	if ((reg_val & XUARTPS_IXR_RTRIG) == 0) {
-		return 0;
-	} else {
-		sys_write32(XUARTPS_IXR_RTRIG, reg_base + XUARTPS_ISR_OFFSET);
-		return 1;
-	}
+	return (reg_val & XUARTPS_SR_RXEMPTY) == 0;
 }
 
 /**
@@ -978,7 +1048,8 @@ static void uart_xlnx_ps_irq_err_enable(const struct device *dev)
 {
 	uintptr_t reg_base = DEVICE_MMIO_GET(dev);
 
-	sys_write32(XUARTPS_IXR_TOVR              /* [12] Transmitter FIFO Overflow */
+	sys_write32(XUARTPS_IXR_RBRK              /* [13] Receiver Break */
+			    | XUARTPS_IXR_TOVR    /* [12] Transmitter FIFO Overflow */
 			    | XUARTPS_IXR_TOUT    /* [8]  Receiver Timerout */
 			    | XUARTPS_IXR_PARITY  /* [7]  Parity Error */
 			    | XUARTPS_IXR_FRAMING /* [6]  Receiver Framing Error */
@@ -997,7 +1068,8 @@ static void uart_xlnx_ps_irq_err_disable(const struct device *dev)
 {
 	uintptr_t reg_base = DEVICE_MMIO_GET(dev);
 
-	sys_write32(XUARTPS_IXR_TOVR              /* [12] Transmitter FIFO Overflow */
+	sys_write32(XUARTPS_IXR_RBRK              /* [13] Receiver Break */
+			    | XUARTPS_IXR_TOVR    /* [12] Transmitter FIFO Overflow */
 			    | XUARTPS_IXR_TOUT    /* [8]  Receiver Timerout */
 			    | XUARTPS_IXR_PARITY  /* [7]  Parity Error */
 			    | XUARTPS_IXR_FRAMING /* [6]  Receiver Framing Error */
@@ -1034,7 +1106,11 @@ static int uart_xlnx_ps_irq_is_pending(const struct device *dev)
  */
 static int uart_xlnx_ps_irq_update(const struct device *dev)
 {
-	ARG_UNUSED(dev);
+	uintptr_t reg_base = DEVICE_MMIO_GET(dev);
+
+	/* Clear RX/TX interrupts */
+	sys_write32(XUARTPS_IXR_TTRIG | XUARTPS_IXR_TXEMPTY | XUARTPS_IXR_RTRIG,
+		    reg_base + XUARTPS_ISR_OFFSET);
 	return 1;
 }
 
@@ -1073,6 +1149,7 @@ static void uart_xlnx_ps_isr(const struct device *dev)
 static DEVICE_API(uart, uart_xlnx_ps_driver_api) = {
 	.poll_in = uart_xlnx_ps_poll_in,
 	.poll_out = uart_xlnx_ps_poll_out,
+	.err_check = uart_xlnx_ps_err_check,
 #ifdef CONFIG_UART_USE_RUNTIME_CONFIGURE
 	.configure = uart_xlnx_ps_configure,
 	.config_get = uart_xlnx_ps_config_get,