[PATCHv3 4/6] serial: mxs-auart: fix IRQ registration ordering and manage console clock

[Rosen Penev]

Move the main UART IRQ registration after uart_add_one_port so that
s->port.state and s->port.lock are initialized before the interrupt
handler can run. Mask all UART interrupts before adding the port to
prevent spurious IRQs left by the bootloader.

After probe succeeds, disable the module clock for non-console ports
since startup will re-enable it on port open. For console ports, keep
the clock prepared so auart_console_write() can safely call
clk_enable() from atomic context.

Guard the IRQ handler and get_mctrl with clk_enable/clk_disable since
GPIO IRQs and serial-core status queries can fire while the clock is
disabled for non-console ports.

In remove, disable the clock for console ports to balance the enable
done in probe, preventing a clock leak on unbind.

Assisted-by: opencode:big-pickle
---
 drivers/tty/serial/mxs-auart.c | 49 +++++++++++++++++++++++++++-------
 1 file changed, 39 insertions(+), 10 deletions(-)

diff --git a/drivers/tty/serial/mxs-auart.c b/drivers/tty/serial/mxs-auart.c
index 4499e3206e85..e2b656638ab3 100644
--- a/drivers/tty/serial/mxs-auart.c
+++ b/drivers/tty/serial/mxs-auart.c
@@ -738,9 +738,13 @@ static u32 mxs_auart_modem_status(struct mxs_auart_port *s, u32 mctrl)
 static u32 mxs_auart_get_mctrl(struct uart_port *u)
 {
 	struct mxs_auart_port *s = to_auart_port(u);
-	u32 stat = mxs_read(s, REG_STAT);
+	u32 stat;
 	u32 mctrl = 0;
 
+	clk_enable(s->clk);
+	stat = mxs_read(s, REG_STAT);
+	clk_disable(s->clk);
+
 	if (stat & AUART_STAT_CTS)
 		mctrl |= TIOCM_CTS;
 
@@ -1079,6 +1083,7 @@ static irqreturn_t mxs_auart_irq_handle(int irq, void *context)
 	struct mxs_auart_port *s = context;
 	u32 mctrl_temp = s->mctrl_prev;
 
+	clk_enable(s->clk);
 	uart_port_lock(&s->port);
 
 	stat = mxs_read(s, REG_STAT);
@@ -1118,6 +1123,7 @@ static irqreturn_t mxs_auart_irq_handle(int irq, void *context)
 	}
 
 	uart_port_unlock(&s->port);
+	clk_disable(s->clk);
 
 	return IRQ_HANDLED;
 }
@@ -1603,10 +1609,6 @@ static int mxs_auart_probe(struct platform_device *pdev)
 	}
 
 	s->port.irq = irq;
-	ret = devm_request_irq(&pdev->dev, irq, mxs_auart_irq_handle, 0,
-			       dev_name(&pdev->dev), s);
-	if (ret)
-		goto out_disable_clk;
 
 	platform_set_drvdata(pdev, s);
 
@@ -1627,9 +1629,28 @@ static int mxs_auart_probe(struct platform_device *pdev)
 
 	mxs_auart_reset_deassert(s);
 
+	/* Mask all UART interrupts to prevent spurious IRQs from bootloader */
+	mxs_write(0, s, REG_INTR);
+
 	ret = uart_add_one_port(&auart_driver, &s->port);
-	if (ret)
-		goto out_free_qpio_irq;
+	if (ret) {
+		auart_port[s->port.line] = NULL;
+		goto out_disable_clk;
+	}
+
+	/*
+	 * Request the main IRQ after uart_add_one_port so that
+	 * s->port.state and s->port.lock are initialized before
+	 * the handler can run in response to a bootloader-left
+	 * interrupt.
+	 */
+	ret = devm_request_irq(&pdev->dev, irq, mxs_auart_irq_handle, 0,
+			       dev_name(&pdev->dev), s);
+	if (ret) {
+		uart_remove_one_port(&auart_driver, &s->port);
+		auart_port[s->port.line] = NULL;
+		goto out_disable_clk;
+	}
 
 	/* ASM9260 don't have version reg */
 	if (is_asm9260_auart(s)) {
@@ -1641,10 +1662,16 @@ static int mxs_auart_probe(struct platform_device *pdev)
 			 (version >> 16) & 0xff, version & 0xffff);
 	}
 
-	return 0;
+	/*
+	 * Disable clock -- startup will re-enable when the port is opened.
+	 * For the console port the clock must stay prepared so that
+	 * auart_console_write() can safely call clk_enable() from
+	 * atomic context.
+	 */
+	if (!uart_console(&s->port))
+		clk_disable_unprepare(s->clk);
 
-out_free_qpio_irq:
-	auart_port[s->port.line] = NULL;
+	return 0;
 
 out_disable_clk:
 	clk_disable_unprepare(s->clk);
@@ -1657,6 +1684,8 @@ static void mxs_auart_remove(struct platform_device *pdev)
 
 	uart_remove_one_port(&auart_driver, &s->port);
 	auart_port[s->port.line] = NULL;
+	if (uart_console(&s->port))
+		clk_disable_unprepare(s->clk);
 }
 
 static struct platform_driver mxs_auart_driver = {
-- 
2.54.0