[PATCH v1 4/6] serial: 8250: Fix corner case for port matching

["Uwe Kleine-König" <ukleinek@kernel.org>]

In the case CONFIG_SERIAL_8250=y + CONFIG_SERIAL_8250_HUB6=m
hub6_match_port() evaluates statically to false in
serial8250_match_port() which is a bug and a change in behavior compared
to before commit 7ab80d1e7243 ("serial: 8250: fix compile error with
hub6_match_port() when compiled as a module").

To make the comparison correct, the dummy implementation of
hub6_match_port() must only be used if CONFIG_SERIAL_8250_HUB6 is
disabled. Then as there is a bidirectional dependency between
8250_hub6.c and 8250_core.c, put both in the same module.

Fixes: 7ab80d1e7243 ("serial: 8250: fix compile error with hub6_match_port() when compiled as a module")
Signed-off-by: Uwe Kleine-König <ukleinek@kernel.org>
---
 drivers/tty/serial/8250/8250.h          | 8 +++++++-
 drivers/tty/serial/8250/8250_hub6.c     | 8 +-------
 drivers/tty/serial/8250/8250_platform.c | 4 ++++
 drivers/tty/serial/8250/Kconfig         | 4 ++--
 drivers/tty/serial/8250/Makefile        | 2 +-
 5 files changed, 15 insertions(+), 11 deletions(-)

diff --git a/drivers/tty/serial/8250/8250.h b/drivers/tty/serial/8250/8250.h
index b62f88eec881..39d72f1480c0 100644
--- a/drivers/tty/serial/8250/8250.h
+++ b/drivers/tty/serial/8250/8250.h
@@ -315,6 +315,12 @@ static inline int serial8250_pnp_init(void) { return 0; }
 static inline void serial8250_pnp_exit(void) { }
 #endif
 
+#ifdef CONFIG_SERIAL_8250_HUB6
+int serial8250_hub6_init(void);
+#else
+static inline int serial8250_hub6_init(void) { return 0; }
+#endif
+
 #ifdef CONFIG_SERIAL_8250_RSA
 void univ8250_rsa_support(struct uart_ops *ops, const struct uart_ops *core_ops);
 void rsa_enable(struct uart_8250_port *up);
@@ -335,7 +341,7 @@ int fintek_8250_probe(struct uart_8250_port *uart);
 static inline int fintek_8250_probe(struct uart_8250_port *uart) { return 0; }
 #endif
 
-#if IS_REACHABLE(CONFIG_SERIAL_8250_HUB6)
+#if IS_ENABLED(CONFIG_SERIAL_8250_HUB6)
 bool hub6_match_port(const struct uart_port *port1, const struct uart_port *port2);
 #else
 static inline bool hub6_match_port(const struct uart_port *port1, const struct uart_port *port2)
diff --git a/drivers/tty/serial/8250/8250_hub6.c b/drivers/tty/serial/8250/8250_hub6.c
index b6767633c966..3e548530ec4e 100644
--- a/drivers/tty/serial/8250/8250_hub6.c
+++ b/drivers/tty/serial/8250/8250_hub6.c
@@ -49,13 +49,7 @@ bool hub6_match_port(const struct uart_port *port1, const struct uart_port *port
 }
 EXPORT_SYMBOL_GPL(hub6_match_port);
 
-static int __init hub6_init(void)
+int __init serial8250_hub6_init(void)
 {
 	return platform_device_register(&hub6_device);
 }
-
-module_init(hub6_init);
-
-MODULE_AUTHOR("Russell King");
-MODULE_DESCRIPTION("8250 serial probe module for Hub6 cards");
-MODULE_LICENSE("GPL");
diff --git a/drivers/tty/serial/8250/8250_platform.c b/drivers/tty/serial/8250/8250_platform.c
index 5a0bc1fae11d..e8524d545de9 100644
--- a/drivers/tty/serial/8250/8250_platform.c
+++ b/drivers/tty/serial/8250/8250_platform.c
@@ -319,6 +319,10 @@ static int __init serial8250_init(void)
 	if (ret)
 		goto unreg_uart_drv;
 
+	ret = serial8250_hub6_init();
+	if (ret)
+		goto unreg_pnp;
+
 	serial8250_isa_devs = platform_device_alloc("serial8250", PLAT8250_DEV_LEGACY);
 	if (!serial8250_isa_devs) {
 		ret = -ENOMEM;
diff --git a/drivers/tty/serial/8250/Kconfig b/drivers/tty/serial/8250/Kconfig
index fc3e58d62233..00c2ced12717 100644
--- a/drivers/tty/serial/8250/Kconfig
+++ b/drivers/tty/serial/8250/Kconfig
@@ -294,8 +294,8 @@ config SERIAL_8250_EXAR_ST16C554
 	  will be called 8250_exar_st16c554.
 
 config SERIAL_8250_HUB6
-	tristate "Support Hub6 cards"
-	depends on SERIAL_8250 != n && ISA && SERIAL_8250_MANY_PORTS
+	bool "Support Hub6 cards"
+	depends on SERIAL_8250_MANY_PORTS && ISA
 	help
 	  Say Y here if you have a HUB6 serial board.
 
diff --git a/drivers/tty/serial/8250/Makefile b/drivers/tty/serial/8250/Makefile
index 6d21402b4435..416c32e3aba2 100644
--- a/drivers/tty/serial/8250/Makefile
+++ b/drivers/tty/serial/8250/Makefile
@@ -7,6 +7,7 @@ obj-$(CONFIG_SERIAL_8250)		+= 8250.o
 8250-y					:= 8250_core.o
 8250-y					+= 8250_platform.o
 8250-$(CONFIG_SERIAL_8250_PNP)		+= 8250_pnp.o
+8250-$(CONFIG_SERIAL_8250_HUB6)		+= 8250_hub6.o
 
 obj-$(CONFIG_SERIAL_8250)		+= 8250_base.o
 8250_base-y				:= 8250_port.o
@@ -35,7 +36,6 @@ obj-$(CONFIG_SERIAL_8250_EXAR_ST16C554)	+= 8250_exar_st16c554.o
 obj-$(CONFIG_SERIAL_8250_FOURPORT)	+= 8250_fourport.o
 obj-$(CONFIG_SERIAL_8250_FSL)		+= 8250_fsl.o
 obj-$(CONFIG_SERIAL_8250_HP300)		+= 8250_hp300.o
-obj-$(CONFIG_SERIAL_8250_HUB6)		+= 8250_hub6.o
 obj-$(CONFIG_SERIAL_8250_INGENIC)	+= 8250_ingenic.o
 obj-$(CONFIG_SERIAL_8250_IOC3)		+= 8250_ioc3.o
 obj-$(CONFIG_SERIAL_8250_KEBA)		+= 8250_keba.o
-- 
2.55.0.11.g153666a7d9bb