serial: 8250: omap: Fix imprecise external abort for omap_8250_pm()

We must idle the uart only after serial8250_unregister_port(). Otherwise
unbinding the uart via sysfs while doing cat on the port produces an
imprecise external abort:

mem_serial_in from omap_8250_pm+0x44/0xf4
omap_8250_pm from uart_hangup+0xe0/0x194
uart_hangup from __tty_hangup.part.0+0x37c/0x3a8
__tty_hangup.part.0 from uart_remove_one_port+0x9c/0x22c
uart_remove_one_port from serial8250_unregister_port+0x60/0xe8
serial8250_unregister_port from omap8250_remove+0x6c/0xd0
omap8250_remove from platform_remove+0x28/0x54

Turns out the driver needs to have runtime PM functional before the
driver probe calls serial8250_register_8250_port(). And it needs
runtime PM after driver remove calls serial8250_unregister_port().

On probe, we need to read registers before registering the port in
omap_serial_fill_features_erratas(). We do that with custom uart_read()
already.

On remove, after serial8250_unregister_port(), we need to write to the
uart registers to idle the device. Let's add a custom uart_write() for
that.

Currently the uart register access depends on port->membase to be
initialized, which won't work after serial8250_unregister_port().
Let's use priv->membase instead, and use it for runtime PM related
functions to remove the dependency to port->membase for early and
late register access.

Note that during use, we need to check for a valid port in the runtime PM
related functions. This is needed for the optional wakeup configuration.
We now need to set the drvdata a bit earlier so it's available for the
runtime PM functions.

With the port checks in runtime PM functions, the old checks for priv in
omap8250_runtime_suspend() and omap8250_runtime_resume() functions are no
longer needed and are removed.
Signed-off-by: Tony Lindgren <tony@atomide.com>
Link: https://lore.kernel.org/r/20230508082014.23083-3-tony@atomide.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/8250/8250_omap.c

@@ -32,6 +32,7 @@
 #include "8250.h"
 
 #define DEFAULT_CLK_SPEED	48000000
+#define OMAP_UART_REGSHIFT	2
 
 #define UART_ERRATA_i202_MDR1_ACCESS	(1 << 0)
 #define OMAP_UART_WER_HAS_TX_WAKEUP	(1 << 1)
@@ -115,6 +116,7 @@
 #define UART_OMAP_RX_LVL		0x19
 
 struct omap8250_priv {
+	void __iomem *membase;
 	int line;
 	u8 habit;
 	u8 mdr1;
@@ -159,9 +161,14 @@ static void omap_8250_rx_dma_flush(struct uart_8250_port *p);
 static inline void omap_8250_rx_dma_flush(struct uart_8250_port *p) { }
 #endif
 
-static u32 uart_read(struct uart_8250_port *up, u32 reg)
+static u32 uart_read(struct omap8250_priv *priv, u32 reg)
 {
-	return readl(up->port.membase + (reg << up->port.regshift));
+	return readl(priv->membase + (reg << OMAP_UART_REGSHIFT));
+}
+
+static void uart_write(struct omap8250_priv *priv, u32 reg, u32 val)
+{
+	writel(val, priv->membase + (reg << OMAP_UART_REGSHIFT));
 }
 
 /*
@@ -548,7 +555,7 @@ static void omap_serial_fill_features_erratas(struct uart_8250_port *up,
 	u32 mvr, scheme;
 	u16 revision, major, minor;
 
-	mvr = uart_read(up, UART_OMAP_MVER);
+	mvr = uart_read(priv, UART_OMAP_MVER);
 
 	/* Check revision register scheme */
 	scheme = mvr >> OMAP_UART_MVR_SCHEME_SHIFT;
@@ -1394,7 +1401,7 @@ static int omap8250_probe(struct platform_device *pdev)
 		UPF_HARD_FLOW;
 	up.port.private_data = priv;
 
-	up.port.regshift = 2;
+	up.port.regshift = OMAP_UART_REGSHIFT;
 	up.port.fifosize = 64;
 	up.tx_loadsz = 64;
 	up.capabilities = UART_CAP_FIFO;
@@ -1457,6 +1464,8 @@ static int omap8250_probe(struct platform_device *pdev)
 			 DEFAULT_CLK_SPEED);
 	}
 
+	priv->membase = membase;
+	priv->line = -ENODEV;
 	priv->latency = PM_QOS_CPU_LATENCY_DEFAULT_VALUE;
 	priv->calc_latency = PM_QOS_CPU_LATENCY_DEFAULT_VALUE;
 	cpu_latency_qos_add_request(&priv->pm_qos_request, priv->latency);
@@ -1464,6 +1473,8 @@ static int omap8250_probe(struct platform_device *pdev)
 
 	spin_lock_init(&priv->rx_dma_lock);
 
+	platform_set_drvdata(pdev, priv);
+
 	device_init_wakeup(&pdev->dev, true);
 	pm_runtime_enable(&pdev->dev);
 	pm_runtime_use_autosuspend(&pdev->dev);
@@ -1525,7 +1536,6 @@ static int omap8250_probe(struct platform_device *pdev)
 		goto err;
 	}
 	priv->line = ret;
-	platform_set_drvdata(pdev, priv);
 	pm_runtime_mark_last_busy(&pdev->dev);
 	pm_runtime_put_autosuspend(&pdev->dev);
 	return 0;
@@ -1547,11 +1557,12 @@ static int omap8250_remove(struct platform_device *pdev)
 	if (err)
 		return err;
 
+	serial8250_unregister_port(priv->line);
+	priv->line = -ENODEV;
 	pm_runtime_dont_use_autosuspend(&pdev->dev);
 	pm_runtime_put_sync(&pdev->dev);
 	flush_work(&priv->qos_work);
 	pm_runtime_disable(&pdev->dev);
-	serial8250_unregister_port(priv->line);
 	cpu_latency_qos_remove_request(&priv->pm_qos_request);
 	device_init_wakeup(&pdev->dev, false);
 	return 0;
@@ -1627,7 +1638,6 @@ static int omap8250_lost_context(struct uart_8250_port *up)
 static int omap8250_soft_reset(struct device *dev)
 {
 	struct omap8250_priv *priv = dev_get_drvdata(dev);
-	struct uart_8250_port *up = serial8250_get_port(priv->line);
 	int timeout = 100;
 	int sysc;
 	int syss;
@@ -1641,20 +1651,20 @@ static int omap8250_soft_reset(struct device *dev)
 	 * needing omap8250_soft_reset() quirk. Do it in two writes as
 	 * recommended in the comment for omap8250_update_scr().
 	 */
-	serial_out(up, UART_OMAP_SCR, OMAP_UART_SCR_DMAMODE_1);
-	serial_out(up, UART_OMAP_SCR,
+	uart_write(priv, UART_OMAP_SCR, OMAP_UART_SCR_DMAMODE_1);
+	uart_write(priv, UART_OMAP_SCR,
 		   OMAP_UART_SCR_DMAMODE_1 | OMAP_UART_SCR_DMAMODE_CTL);
 
-	sysc = serial_in(up, UART_OMAP_SYSC);
+	sysc = uart_read(priv, UART_OMAP_SYSC);
 
 	/* softreset the UART */
 	sysc |= OMAP_UART_SYSC_SOFTRESET;
-	serial_out(up, UART_OMAP_SYSC, sysc);
+	uart_write(priv, UART_OMAP_SYSC, sysc);
 
 	/* By experiments, 1us enough for reset complete on AM335x */
 	do {
 		udelay(1);
-		syss = serial_in(up, UART_OMAP_SYSS);
+		syss = uart_read(priv, UART_OMAP_SYSS);
 	} while (--timeout && !(syss & OMAP_UART_SYSS_RESETDONE));
 
 	if (!timeout) {
@@ -1668,13 +1678,10 @@ static int omap8250_soft_reset(struct device *dev)
 static int omap8250_runtime_suspend(struct device *dev)
 {
 	struct omap8250_priv *priv = dev_get_drvdata(dev);
-	struct uart_8250_port *up;
-
-	/* In case runtime-pm tries this before we are setup */
-	if (!priv)
-		return 0;
+	struct uart_8250_port *up = NULL;
 
-	up = serial8250_get_port(priv->line);
+	if (priv->line >= 0)
+		up = serial8250_get_port(priv->line);
 	/*
 	 * When using 'no_console_suspend', the console UART must not be
 	 * suspended. Since driver suspend is managed by runtime suspend,
@@ -1682,7 +1689,7 @@ static int omap8250_runtime_suspend(struct device *dev)
 	 * active during suspend.
 	 */
 	if (priv->is_suspending && !console_suspend_enabled) {
-		if (uart_console(&up->port))
+		if (up && uart_console(&up->port))
 			return -EBUSY;
 	}
 
@@ -1693,13 +1700,15 @@ static int omap8250_runtime_suspend(struct device *dev)
 		if (ret)
 			return ret;
 
-		/* Restore to UART mode after reset (for wakeup) */
-		omap8250_update_mdr1(up, priv);
-		/* Restore wakeup enable register */
-		serial_out(up, UART_OMAP_WER, priv->wer);
+		if (up) {
+			/* Restore to UART mode after reset (for wakeup) */
+			omap8250_update_mdr1(up, priv);
+			/* Restore wakeup enable register */
+			serial_out(up, UART_OMAP_WER, priv->wer);
+		}
 	}
 
-	if (up->dma && up->dma->rxchan)
+	if (up && up->dma && up->dma->rxchan)
 		omap_8250_rx_dma_flush(up);
 
 	priv->latency = PM_QOS_CPU_LATENCY_DEFAULT_VALUE;
@@ -1711,18 +1720,15 @@ static int omap8250_runtime_suspend(struct device *dev)
 static int omap8250_runtime_resume(struct device *dev)
 {
 	struct omap8250_priv *priv = dev_get_drvdata(dev);
-	struct uart_8250_port *up;
-
-	/* In case runtime-pm tries this before we are setup */
-	if (!priv)
-		return 0;
+	struct uart_8250_port *up = NULL;
 
-	up = serial8250_get_port(priv->line);
+	if (priv->line >= 0)
+		up = serial8250_get_port(priv->line);
 
-	if (omap8250_lost_context(up))
+	if (up && omap8250_lost_context(up))
 		omap8250_restore_regs(up);
 
-	if (up->dma && up->dma->rxchan && !(priv->habit & UART_HAS_EFR2))
+	if (up && up->dma && up->dma->rxchan && !(priv->habit & UART_HAS_EFR2))
 		omap_8250_rx_dma(up);
 
 	priv->latency = priv->calc_latency;