From: Ilpo Järvinen ilpo.jarvinen@linux.intel.com
commit f9b11229b79c0fb2100b5bb4628a101b1d37fbf6 upstream.
When console is enabled, univ8250_console_setup() calls serial8250_console_setup() before .dev is set to uart_port. Therefore, it will not call pm_runtime_get_sync(). Later, when the actual driver is going to take over univ8250_console_exit() is called. As .dev is already set, serial8250_console_exit() makes pm_runtime_put_sync() call with usage count being zero triggering PM usage count warning (extra debug for univ8250_console_setup(), univ8250_console_exit(), and serial8250_register_ports()):
[ 0.068987] univ8250_console_setup ttyS0 nodev [ 0.499670] printk: console [ttyS0] enabled [ 0.717955] printk: console [ttyS0] printing thread started [ 1.960163] serial8250_register_ports assigned dev for ttyS0 [ 1.976830] printk: console [ttyS0] disabled [ 1.976888] printk: console [ttyS0] printing thread stopped [ 1.977073] univ8250_console_exit ttyS0 usage:0 [ 1.977075] serial8250 serial8250: Runtime PM usage count underflow! [ 1.977429] dw-apb-uart.6: ttyS0 at MMIO 0x4010006000 (irq = 33, base_baud = 115200) is a 16550A [ 1.977812] univ8250_console_setup ttyS0 usage:2 [ 1.978167] printk: console [ttyS0] printing thread started [ 1.978203] printk: console [ttyS0] enabled
To fix the issue, call pm_runtime_get_sync() in serial8250_register_ports() as soon as .dev is set for an uart_port if it has console enabled.
This problem became apparent only recently because 82586a721595 ("PM: runtime: Avoid device usage count underflows") added the warning printout. I confirmed this problem also occurs with v5.18 (w/o the warning printout, obviously).
Fixes: bedb404e91bb ("serial: 8250_port: Don't use power management for kernel console") Cc: stable stable@kernel.org Tested-by: Tony Lindgren tony@atomide.com Reviewed-by: Andy Shevchenko andriy.shevchenko@linux.intel.com Reviewed-by: Tony Lindgren tony@atomide.com Signed-off-by: Ilpo Järvinen ilpo.jarvinen@linux.intel.com Link: https://lore.kernel.org/r/b4f428e9-491f-daf2-2232-819928dc276e@linux.intel.c... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/tty/serial/8250/8250_core.c | 4 ++++ drivers/tty/serial/serial_core.c | 5 ----- include/linux/serial_core.h | 5 +++++ 3 files changed, 9 insertions(+), 5 deletions(-)
--- a/drivers/tty/serial/8250/8250_core.c +++ b/drivers/tty/serial/8250/8250_core.c @@ -23,6 +23,7 @@ #include <linux/sysrq.h> #include <linux/delay.h> #include <linux/platform_device.h> +#include <linux/pm_runtime.h> #include <linux/tty.h> #include <linux/ratelimit.h> #include <linux/tty_flip.h> @@ -560,6 +561,9 @@ serial8250_register_ports(struct uart_dr
up->port.dev = dev;
+ if (uart_console_enabled(&up->port)) + pm_runtime_get_sync(up->port.dev); + serial8250_apply_quirks(up); uart_add_one_port(drv, &up->port); } --- a/drivers/tty/serial/serial_core.c +++ b/drivers/tty/serial/serial_core.c @@ -1904,11 +1904,6 @@ static int uart_proc_show(struct seq_fil } #endif
-static inline bool uart_console_enabled(struct uart_port *port) -{ - return uart_console(port) && (port->cons->flags & CON_ENABLED); -} - static void uart_port_spin_lock_init(struct uart_port *port) { spin_lock_init(&port->lock); --- a/include/linux/serial_core.h +++ b/include/linux/serial_core.h @@ -388,6 +388,11 @@ static const bool earlycon_acpi_spcr_ena static inline int setup_earlycon(char *buf) { return 0; } #endif
+static inline bool uart_console_enabled(struct uart_port *port) +{ + return uart_console(port) && (port->cons->flags & CON_ENABLED); +} + struct uart_port *uart_get_console(struct uart_port *ports, int nr, struct console *c); int uart_parse_earlycon(char *p, unsigned char *iotype, resource_size_t *addr,