[PATCH 02/18] serial: sc16is7xx: fix invalid sc16is7xx_lines bitfield in case of probe error

[Hugo Villeneuve]

From: Hugo Villeneuve <hvilleneuve@xxxxxxxxxxxx>

If an error occurs during probing, the sc16is7xx_lines bitfield may be left
in a state that doesn't represent the correct state of lines allocation.

For example, in a system with two SC16 devices, if an error occurs only
during probing of channel (port) B of the second device, sc16is7xx_lines
final state will be 00001011b instead of the expected 00000011b.

This is caused in part because of the "i--" in the for/loop located in
the out_ports: error path.

Fix this by checking the return value of uart_add_one_port() and set line
allocation bit only if this was successful. This allows the refactor of
the obfuscated for(i--...) loop in the error path, and properly call
uart_remove_one_port() only when needed, and properly unset line allocation
bits.

Also use same mechanism in remove() when calling uart_remove_one_port().

Fixes: c64349722d14 ("sc16is7xx: support multiple devices")
Cc: stable@xxxxxxxxxxxxxxx
Cc: Yury Norov <yury.norov@xxxxxxxxx>
Signed-off-by: Hugo Villeneuve <hvilleneuve@xxxxxxxxxxxx>
---
There is already a patch by Yury Norov <yury.norov@xxxxxxxxx> to simplify
sc16is7xx_alloc_line():
https://lore.kernel.org/all/20231212022749.625238-30-yury.norov@xxxxxxxxx/

Since my patch gets rid of sc16is7xx_alloc_line() entirely, it would make
Yury's patch unnecessary.
---
 drivers/tty/serial/sc16is7xx.c | 44 ++++++++++++++--------------------
 1 file changed, 18 insertions(+), 26 deletions(-)

diff --git a/drivers/tty/serial/sc16is7xx.c b/drivers/tty/serial/sc16is7xx.c
index b585663c1e6e..b92fd01cfeec 100644
--- a/drivers/tty/serial/sc16is7xx.c
+++ b/drivers/tty/serial/sc16is7xx.c
@@ -407,19 +407,6 @@ static void sc16is7xx_port_update(struct uart_port *port, u8 reg,
 	regmap_update_bits(one->regmap, reg, mask, val);
 }
 
-static int sc16is7xx_alloc_line(void)
-{
-	int i;
-
-	BUILD_BUG_ON(SC16IS7XX_MAX_DEVS > BITS_PER_LONG);
-
-	for (i = 0; i < SC16IS7XX_MAX_DEVS; i++)
-		if (!test_and_set_bit(i, &sc16is7xx_lines))
-			break;
-
-	return i;
-}
-
 static void sc16is7xx_power(struct uart_port *port, int on)
 {
 	sc16is7xx_port_update(port, SC16IS7XX_IER_REG,
@@ -1550,6 +1537,13 @@ static int sc16is7xx_probe(struct device *dev,
 		     SC16IS7XX_IOCONTROL_SRESET_BIT);
 
 	for (i = 0; i < devtype->nr_uart; ++i) {
+		s->p[i].port.line = find_first_zero_bit(&sc16is7xx_lines,
+							SC16IS7XX_MAX_DEVS);
+		if (s->p[i].port.line >= SC16IS7XX_MAX_DEVS) {
+			ret = -ERANGE;
+			goto out_ports;
+		}
+
 		/* Initialize port data */
 		s->p[i].port.dev	= dev;
 		s->p[i].port.irq	= irq;
@@ -1569,14 +1563,8 @@ static int sc16is7xx_probe(struct device *dev,
 		s->p[i].port.rs485_supported = sc16is7xx_rs485_supported;
 		s->p[i].port.ops	= &sc16is7xx_ops;
 		s->p[i].old_mctrl	= 0;
-		s->p[i].port.line	= sc16is7xx_alloc_line();
 		s->p[i].regmap		= regmaps[i];
 
-		if (s->p[i].port.line >= SC16IS7XX_MAX_DEVS) {
-			ret = -ENOMEM;
-			goto out_ports;
-		}
-
 		mutex_init(&s->p[i].efr_lock);
 
 		ret = uart_get_rs485_mode(&s->p[i].port);
@@ -1594,8 +1582,13 @@ static int sc16is7xx_probe(struct device *dev,
 		kthread_init_work(&s->p[i].tx_work, sc16is7xx_tx_proc);
 		kthread_init_work(&s->p[i].reg_work, sc16is7xx_reg_proc);
 		kthread_init_delayed_work(&s->p[i].ms_work, sc16is7xx_ms_proc);
+
 		/* Register port */
-		uart_add_one_port(&sc16is7xx_uart, &s->p[i].port);
+		ret = uart_add_one_port(&sc16is7xx_uart, &s->p[i].port);
+		if (ret)
+			goto out_ports;
+
+		set_bit(s->p[i].port.line, &sc16is7xx_lines);
 
 		/* Enable EFR */
 		sc16is7xx_port_write(&s->p[i].port, SC16IS7XX_LCR_REG,
@@ -1653,10 +1646,9 @@ static int sc16is7xx_probe(struct device *dev,
 #endif
 
 out_ports:
-	for (i--; i >= 0; i--) {
-		uart_remove_one_port(&sc16is7xx_uart, &s->p[i].port);
-		clear_bit(s->p[i].port.line, &sc16is7xx_lines);
-	}
+	for (i = 0; i < devtype->nr_uart; i++)
+		if (test_and_clear_bit(s->p[i].port.line, &sc16is7xx_lines))
+			uart_remove_one_port(&sc16is7xx_uart, &s->p[i].port);
 
 	kthread_stop(s->kworker_task);
 
@@ -1683,8 +1675,8 @@ static void sc16is7xx_remove(struct device *dev)
 
 	for (i = 0; i < s->devtype->nr_uart; i++) {
 		kthread_cancel_delayed_work_sync(&s->p[i].ms_work);
-		uart_remove_one_port(&sc16is7xx_uart, &s->p[i].port);
-		clear_bit(s->p[i].port.line, &sc16is7xx_lines);
+		if (test_and_clear_bit(s->p[i].port.line, &sc16is7xx_lines))
+			uart_remove_one_port(&sc16is7xx_uart, &s->p[i].port);
 		sc16is7xx_power(&s->p[i].port, 0);
 	}
 
-- 
2.39.2