serial: tegra: Add PIO mode support

Add PIO mode support in receive and transmit path with RX interrupt
trigger of 16 bytes for Tegra194 and older chips.

Signed-off-by: Shardar Shariff Md <smohammed@nvidia.com>
Signed-off-by: Krishna Yarlagadda <kyarlagadda@nvidia.com>
Link: https://lore.kernel.org/r/1567572187-29820-13-git-send-email-kyarlagadda@nvidia.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/serial-tegra.c

@@ -139,6 +139,8 @@ struct tegra_uart_port {
 	int					n_adjustable_baud_rates;
 	int					required_rate;
 	int					configured_rate;
+	bool					use_rx_pio;
+	bool					use_tx_pio;
 };
 
 static void tegra_uart_start_next_tx(struct tegra_uart_port *tup);
@@ -567,7 +569,7 @@ static void tegra_uart_start_next_tx(struct tegra_uart_port *tup)
 	if (!count)
 		return;
 
-	if (count < TEGRA_UART_MIN_DMA)
+	if (tup->use_tx_pio || count < TEGRA_UART_MIN_DMA)
 		tegra_uart_start_pio_tx(tup, count);
 	else if (BYTES_TO_ALIGN(tail) > 0)
 		tegra_uart_start_pio_tx(tup, BYTES_TO_ALIGN(tail));
@@ -800,6 +802,18 @@ static void tegra_uart_handle_modem_signal_change(struct uart_port *u)
 		uart_handle_cts_change(&tup->uport, msr & UART_MSR_CTS);
 }
 
+static void do_handle_rx_pio(struct tegra_uart_port *tup)
+{
+	struct tty_struct *tty = tty_port_tty_get(&tup->uport.state->port);
+	struct tty_port *port = &tup->uport.state->port;
+
+	tegra_uart_handle_rx_pio(tup, port);
+	if (tty) {
+		tty_flip_buffer_push(port);
+		tty_kref_put(tty);
+	}
+}
+
 static irqreturn_t tegra_uart_isr(int irq, void *data)
 {
 	struct tegra_uart_port *tup = data;
@@ -813,7 +827,7 @@ static irqreturn_t tegra_uart_isr(int irq, void *data)
 	while (1) {
 		iir = tegra_uart_read(tup, UART_IIR);
 		if (iir & UART_IIR_NO_INT) {
-			if (is_rx_int) {
+			if (!tup->use_rx_pio && is_rx_int) {
 				tegra_uart_handle_rx_dma(tup);
 				if (tup->rx_in_progress) {
 					ier = tup->ier_shadow;
@@ -841,7 +855,7 @@ static irqreturn_t tegra_uart_isr(int irq, void *data)
 		case 4: /* End of data */
 		case 6: /* Rx timeout */
 		case 2: /* Receive */
-			if (!is_rx_int) {
+			if (!tup->use_rx_pio && !is_rx_int) {
 				is_rx_int = true;
 				/* Disable Rx interrupts */
 				ier = tup->ier_shadow;
@@ -851,6 +865,8 @@ static irqreturn_t tegra_uart_isr(int irq, void *data)
 					UART_IER_RTOIE | TEGRA_UART_IER_EORD);
 				tup->ier_shadow = ier;
 				tegra_uart_write(tup, ier, UART_IER);
+			} else {
+				do_handle_rx_pio(tup);
 			}
 			break;
 
@@ -869,6 +885,7 @@ static irqreturn_t tegra_uart_isr(int irq, void *data)
 static void tegra_uart_stop_rx(struct uart_port *u)
 {
 	struct tegra_uart_port *tup = to_tegra_uport(u);
+	struct tty_port *port = &tup->uport.state->port;
 	struct dma_tx_state state;
 	unsigned long ier;
 
@@ -886,9 +903,13 @@ static void tegra_uart_stop_rx(struct uart_port *u)
 	tup->ier_shadow = ier;
 	tegra_uart_write(tup, ier, UART_IER);
 	tup->rx_in_progress = 0;
-	dmaengine_terminate_all(tup->rx_dma_chan);
+	if (tup->rx_dma_chan && !tup->use_rx_pio) {
-	dmaengine_tx_status(tup->rx_dma_chan, tup->rx_cookie, &state);
+		dmaengine_terminate_all(tup->rx_dma_chan);
-	tegra_uart_rx_buffer_push(tup, state.residue);
+		dmaengine_tx_status(tup->rx_dma_chan, tup->rx_cookie, &state);
+		tegra_uart_rx_buffer_push(tup, state.residue);
+	} else {
+		tegra_uart_handle_rx_pio(tup, port);
+	}
 }
 
 static void tegra_uart_hw_deinit(struct tegra_uart_port *tup)
@@ -939,8 +960,10 @@ static void tegra_uart_hw_deinit(struct tegra_uart_port *tup)
 	tup->rx_in_progress = 0;
 	tup->tx_in_progress = 0;
 
-	tegra_uart_dma_channel_free(tup, true);
+	if (!tup->use_rx_pio)
-	tegra_uart_dma_channel_free(tup, false);
+		tegra_uart_dma_channel_free(tup, true);
+	if (!tup->use_tx_pio)
+		tegra_uart_dma_channel_free(tup, false);
 
 	clk_disable_unprepare(tup->uart_clk);
 }
@@ -985,10 +1008,14 @@ static int tegra_uart_hw_init(struct tegra_uart_port *tup)
 	 */
 	tup->fcr_shadow = UART_FCR_ENABLE_FIFO;
 
-	if (tup->cdata->max_dma_burst_bytes == 8)
+	if (tup->use_rx_pio) {
-		tup->fcr_shadow |= UART_FCR_R_TRIG_10;
+		tup->fcr_shadow |= UART_FCR_R_TRIG_11;
-	else
+	} else {
-		tup->fcr_shadow |= UART_FCR_R_TRIG_01;
+		if (tup->cdata->max_dma_burst_bytes == 8)
+			tup->fcr_shadow |= UART_FCR_R_TRIG_10;
+		else
+			tup->fcr_shadow |= UART_FCR_R_TRIG_01;
+	}
 
 	tup->fcr_shadow |= TEGRA_UART_TX_TRIG_16B;
 	tegra_uart_write(tup, tup->fcr_shadow, UART_FCR);
@@ -1016,19 +1043,23 @@ static int tegra_uart_hw_init(struct tegra_uart_port *tup)
 	 * (115200, N, 8, 1) so that the receive DMA buffer may be
 	 * enqueued
 	 */
-	tup->lcr_shadow = TEGRA_UART_DEFAULT_LSR;
 	ret = tegra_set_baudrate(tup, TEGRA_UART_DEFAULT_BAUD);
 	if (ret < 0) {
 		dev_err(tup->uport.dev, "Failed to set baud rate\n");
 		return ret;
 	}
-	tup->fcr_shadow |= UART_FCR_DMA_SELECT;
+	if (!tup->use_rx_pio) {
-	tegra_uart_write(tup, tup->fcr_shadow, UART_FCR);
+		tup->lcr_shadow = TEGRA_UART_DEFAULT_LSR;
+		tup->fcr_shadow |= UART_FCR_DMA_SELECT;
+		tegra_uart_write(tup, tup->fcr_shadow, UART_FCR);
 
-	ret = tegra_uart_start_rx_dma(tup);
+		ret = tegra_uart_start_rx_dma(tup);
-	if (ret < 0) {
+		if (ret < 0) {
-		dev_err(tup->uport.dev, "Not able to start Rx DMA\n");
+			dev_err(tup->uport.dev, "Not able to start Rx DMA\n");
-		return ret;
+			return ret;
+		}
+	} else {
+		tegra_uart_write(tup, tup->fcr_shadow, UART_FCR);
 	}
 	tup->rx_in_progress = 1;
 
@@ -1050,7 +1081,12 @@ static int tegra_uart_hw_init(struct tegra_uart_port *tup)
 	 * both the EORD as well as RX_TIMEOUT - SW sees RX_TIMEOUT first
 	 * then the EORD.
 	 */
-	tup->ier_shadow = UART_IER_RLSI | UART_IER_RTOIE | TEGRA_UART_IER_EORD;
+	if (!tup->use_rx_pio)
+		tup->ier_shadow = UART_IER_RLSI | UART_IER_RTOIE |
+			TEGRA_UART_IER_EORD;
+	else
+		tup->ier_shadow = UART_IER_RLSI | UART_IER_RTOIE | UART_IER_RDI;
+
 	tegra_uart_write(tup, tup->ier_shadow, UART_IER);
 	return 0;
 }
@@ -1145,16 +1181,22 @@ static int tegra_uart_startup(struct uart_port *u)
 	struct tegra_uart_port *tup = to_tegra_uport(u);
 	int ret;
 
-	ret = tegra_uart_dma_channel_allocate(tup, false);
+	if (!tup->use_tx_pio) {
-	if (ret < 0) {
+		ret = tegra_uart_dma_channel_allocate(tup, false);
-		dev_err(u->dev, "Tx Dma allocation failed, err = %d\n", ret);
+		if (ret < 0) {
-		return ret;
+			dev_err(u->dev, "Tx Dma allocation failed, err = %d\n",
+				ret);
+			return ret;
+		}
 	}
 
-	ret = tegra_uart_dma_channel_allocate(tup, true);
+	if (!tup->use_rx_pio) {
-	if (ret < 0) {
+		ret = tegra_uart_dma_channel_allocate(tup, true);
-		dev_err(u->dev, "Rx Dma allocation failed, err = %d\n", ret);
+		if (ret < 0) {
-		goto fail_rx_dma;
+			dev_err(u->dev, "Rx Dma allocation failed, err = %d\n",
+				ret);
+			goto fail_rx_dma;
+		}
 	}
 
 	ret = tegra_uart_hw_init(tup);
@@ -1172,9 +1214,11 @@ static int tegra_uart_startup(struct uart_port *u)
 	return 0;
 
 fail_hw_init:
-	tegra_uart_dma_channel_free(tup, true);
+	if (!tup->use_rx_pio)
+		tegra_uart_dma_channel_free(tup, true);
 fail_rx_dma:
-	tegra_uart_dma_channel_free(tup, false);
+	if (!tup->use_tx_pio)
+		tegra_uart_dma_channel_free(tup, false);
 	return ret;
 }
 
@@ -1378,7 +1422,6 @@ static int tegra_uart_parse_dt(struct platform_device *pdev,
 	int count;
 	int n_entries;
 
-
 	port = of_alias_get_id(np, "serial");
 	if (port < 0) {
 		dev_err(&pdev->dev, "failed to get alias id, errno %d\n", port);
@@ -1388,6 +1431,18 @@ static int tegra_uart_parse_dt(struct platform_device *pdev,
 
 	tup->enable_modem_interrupt = of_property_read_bool(np,
 					"nvidia,enable-modem-interrupt");
+
+	index = of_property_match_string(np, "dma-names", "rx");
+	if (index < 0) {
+		tup->use_rx_pio = true;
+		dev_info(&pdev->dev, "RX in PIO mode\n");
+	}
+	index = of_property_match_string(np, "dma-names", "tx");
+	if (index < 0) {
+		tup->use_tx_pio = true;
+		dev_info(&pdev->dev, "TX in PIO mode\n");
+	}
+
 	n_entries = of_property_count_u32_elems(np, "nvidia,adjust-baud-rates");
 	if (n_entries > 0) {
 		tup->n_adjustable_baud_rates = n_entries / 3;