[RFC PATCH] serial: 8250_omap: provide complete custom startup & shutdown callbacks

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

The currently in-use port->startup and port->shutdown are "okay". The
startup part for instance does the tiny omap extra part and invokes
serial8250_do_startup() for the remaining pieces. The workflow in
serial8250_do_startup() is okay except for the part where UART_RX is
read without a check if there is something to read. I tried to
workaround it in commit 0aa525d1 ("tty: serial: 8250_core: read only
RX if there is something in the FIFO") but then reverted it later in
commit ca8bb4aefb9 ("serial: 8250: Revert "tty: serial: 8250_core: read
only RX if there is something in the FIFO"").

This is the second attempt to get it to work on older OMAPs without
breaking other chips this time :)
Peter Hurley suggested to pull in the few needed lines from
serial8250_do_startup() and drop everything else that is not required
including makeing it simpler like using just request_irq() instead the
chain handler like it is doing now.
So lets try that.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
Peter is this what you had in mind? If so I will repost it without the
RFC. And I think tony would like a stable + fixes tag for it.

 drivers/tty/serial/8250/8250_omap.c | 81 ++++++++++++++++++++++++++++++++-----
 1 file changed, 72 insertions(+), 9 deletions(-)

diff --git a/drivers/tty/serial/8250/8250_omap.c b/drivers/tty/serial/8250/8250_omap.c
index 9289999cb7c6..7fd02a03c1ed 100644
--- a/drivers/tty/serial/8250/8250_omap.c
+++ b/drivers/tty/serial/8250/8250_omap.c
@@ -562,12 +562,36 @@ static irqreturn_t omap_wake_irq(int irq, void *dev_id)
 	return IRQ_NONE;
 }
 
+#ifdef CONFIG_SERIAL_8250_DMA
+static int omap_8250_dma_handle_irq(struct uart_port *port);
+#endif
+
+static irqreturn_t omap8250_irq(int irq, void *dev_id)
+{
+	struct uart_port *port = dev_id;
+	struct uart_8250_port *up = up_to_u8250p(port);
+	unsigned int iir;
+	int ret;
+
+#ifdef CONFIG_SERIAL_8250_DMA
+	if (up->dma) {
+		ret = omap_8250_dma_handle_irq(port);
+		return IRQ_RETVAL(ret);
+	}
+#endif
+
+	serial8250_rpm_get(up);
+	iir = serial_port_in(port, UART_IIR);
+	ret = serial8250_handle_irq(port, iir);
+	serial8250_rpm_put(up);
+
+	return IRQ_RETVAL(ret);
+}
+
 static int omap_8250_startup(struct uart_port *port)
 {
-	struct uart_8250_port *up =
-		container_of(port, struct uart_8250_port, port);
+	struct uart_8250_port *up = up_to_u8250p(port);
 	struct omap8250_priv *priv = port->private_data;
-
 	int ret;
 
 	if (priv->wakeirq) {
@@ -580,10 +604,31 @@ static int omap_8250_startup(struct uart_port *port)
 
 	pm_runtime_get_sync(port->dev);
 
-	ret = serial8250_do_startup(port);
-	if (ret)
+	up->mcr = 0;
+	serial_out(up, UART_FCR, UART_FCR_CLEAR_RCVR | UART_FCR_CLEAR_XMIT);
+
+	serial_port_out(port, UART_LCR, UART_LCR_WLEN8);
+
+	up->lsr_saved_flags = 0;
+	up->msr_saved_flags = 0;
+
+	if (up->dma) {
+		ret = serial8250_request_dma(up);
+		if (ret) {
+			dev_warn_ratelimited(port->dev,
+					     "failed to request DMA\n");
+			up->dma = NULL;
+		}
+	}
+
+	ret = request_irq(port->irq, omap8250_irq, IRQF_SHARED,
+			  dev_name(port->dev), port);
+	if (ret < 0)
 		goto err;
 
+	up->ier = UART_IER_RLSI | UART_IER_RDI;
+	serial_port_out(port, UART_IER, up->ier);
+
 #ifdef CONFIG_PM
 	up->capabilities |= UART_CAP_RPM;
 #endif
@@ -610,8 +655,7 @@ static int omap_8250_startup(struct uart_port *port)
 
 static void omap_8250_shutdown(struct uart_port *port)
 {
-	struct uart_8250_port *up =
-		container_of(port, struct uart_8250_port, port);
+	struct uart_8250_port *up = up_to_u8250p(port);
 	struct omap8250_priv *priv = port->private_data;
 
 	flush_work(&priv->qos_work);
@@ -621,11 +665,24 @@ static void omap_8250_shutdown(struct uart_port *port)
 	pm_runtime_get_sync(port->dev);
 
 	serial_out(up, UART_OMAP_WER, 0);
-	serial8250_do_shutdown(port);
+
+	up->ier = 0;
+	serial_port_out(port, UART_IER, 0);
+
+	if (up->dma)
+		serial8250_release_dma(up);
+
+	/*
+	 * Disable break condition and FIFOs
+	 */
+	if (up->lcr & UART_LCR_SBC)
+		serial_port_out(port, UART_LCR, up->lcr & ~UART_LCR_SBC);
+	serial_out(up, UART_FCR, UART_FCR_CLEAR_RCVR | UART_FCR_CLEAR_XMIT);
 
 	pm_runtime_mark_last_busy(port->dev);
 	pm_runtime_put_autosuspend(port->dev);
 
+	free_irq(port->irq, port);
 	if (priv->wakeirq)
 		free_irq(priv->wakeirq, port);
 }
@@ -974,6 +1031,12 @@ static inline int omap_8250_rx_dma(struct uart_8250_port *p, unsigned int iir)
 }
 #endif
 
+static int omap8250_no_handle_irq(struct uart_port *port)
+{
+	WARN_ONCE(1, "This shouldn't be used\n");
+	return 0;
+}
+
 static int omap8250_probe(struct platform_device *pdev)
 {
 	struct resource *regs = platform_get_resource(pdev, IORESOURCE_MEM, 0);
@@ -1075,6 +1138,7 @@ static int omap8250_probe(struct platform_device *pdev)
 	pm_runtime_get_sync(&pdev->dev);
 
 	omap_serial_fill_features_erratas(&up, priv);
+	up.port.handle_irq = omap8250_no_handle_irq;
 #ifdef CONFIG_SERIAL_8250_DMA
 	if (pdev->dev.of_node) {
 		/*
@@ -1088,7 +1152,6 @@ static int omap8250_probe(struct platform_device *pdev)
 		ret = of_property_count_strings(pdev->dev.of_node, "dma-names");
 		if (ret == 2) {
 			up.dma = &priv->omap8250_dma;
-			up.port.handle_irq = omap_8250_dma_handle_irq;
 			priv->omap8250_dma.fn = the_no_dma_filter_fn;
 			priv->omap8250_dma.tx_dma = omap_8250_tx_dma;
 			priv->omap8250_dma.rx_dma = omap_8250_rx_dma;
-- 
2.1.4