Hi Andy, On Sun, May 24, 2020 at 7:11 PM Guenter Roeck <linux@xxxxxxxxxxxx> wrote: > On Mon, Feb 17, 2020 at 01:40:12PM +0200, Andy Shevchenko wrote: > > In the future we would like to disable power management on the serial devices > > used as kernel consoles to avoid weird behaviour in some cases. However, > > disabling PM may prevent system to go to deep sleep states, which in its turn > > leads to the higher power consumption. > > > > Tony Lindgren proposed a work around, i.e. allow user to detach such consoles > > to make PM working again. In case user wants to see what's going on, it also > > provides a mechanism to attach console back. > > > > Link: https://lists.openwall.net/linux-kernel/2018/09/29/65 > > Suggested-by: Tony Lindgren <tony@xxxxxxxxxxx> > > Signed-off-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx> > > --- a/drivers/tty/serial/serial_core.c > > +++ b/drivers/tty/serial/serial_core.c > > @@ -1919,7 +1919,7 @@ static inline bool uart_console_enabled(struct uart_port *port) > > */ > > static inline void uart_port_spin_lock_init(struct uart_port *port) > > { > > - if (uart_console_enabled(port)) > > + if (uart_console(port)) > > This results in lockdep splashes such as the one attached below. Is there Or "BUG: spinlock bad magic on CPU#3, swapper/0/1", cfr. [1]. So far I hadn't noticed that, as the issue only shows up when using the legacy way of passing a "console=ttyS*" kernel command line parameter, and not when relying on the modern "chosen/stdout-path" DT property. > any special reason for this change ? It is not really explained in the > commit description. Indeed. Why this change? I also don't agree with your typical fix for drivers, which is like: @@ -567,6 +567,9 @@ static int hv_probe(struct platform_device *op) sunserial_console_match(&sunhv_console, op->dev.of_node, &sunhv_reg, port->line, false); + /* We need to initialize lock even for non-registered console */ + spin_lock_init(&port->lock); + err = uart_add_one_port(&sunhv_reg, port); ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ calls uart_port_spin_lock_init() if (err) goto out_unregister_driver; as this initializes the spinlock twice for non-console= ports. > [ 15.439094] INFO: trying to register non-static key. > [ 15.439146] the code is fine but needs lockdep annotation. > [ 15.439196] turning off the locking correctness validator. > [ 15.439392] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.7.0-rc6-00244-gcaffb99b6929 #1 > [ 15.439469] Hardware name: Freescale i.MX6 Ultralite (Device Tree) > [ 15.439887] [<c0112578>] (unwind_backtrace) from [<c010c4f4>] (show_stack+0x10/0x14) > [ 15.439982] [<c010c4f4>] (show_stack) from [<c06dfcb0>] (dump_stack+0xe4/0x11c) > [ 15.440053] [<c06dfcb0>] (dump_stack) from [<c01883e4>] (register_lock_class+0x8a0/0x924) > [ 15.440127] [<c01883e4>] (register_lock_class) from [<c01884d4>] (__lock_acquire+0x6c/0x2e80) > [ 15.440202] [<c01884d4>] (__lock_acquire) from [<c018756c>] (lock_acquire+0xf8/0x4f4) > [ 15.440274] [<c018756c>] (lock_acquire) from [<c0ddf02c>] (_raw_spin_lock_irqsave+0x50/0x64) > [ 15.440350] [<c0ddf02c>] (_raw_spin_lock_irqsave) from [<c07af5d8>] (uart_add_one_port+0x3a4/0x504) > [ 15.440431] [<c07af5d8>] (uart_add_one_port) from [<c089c990>] (platform_drv_probe+0x48/0x98) > [ 15.440506] [<c089c990>] (platform_drv_probe) from [<c089a708>] (really_probe+0x214/0x344) > [ 15.440578] [<c089a708>] (really_probe) from [<c089a948>] (driver_probe_device+0x5c/0x16c) > [ 15.440650] [<c089a948>] (driver_probe_device) from [<c089ac00>] (device_driver_attach+0x58/0x60) > [ 15.440727] [<c089ac00>] (device_driver_attach) from [<c089ac8c>] (__driver_attach+0x84/0xc0) > [ 15.440800] [<c089ac8c>] (__driver_attach) from [<c08987e8>] (bus_for_each_dev+0x70/0xb4) > [ 15.440874] [<c08987e8>] (bus_for_each_dev) from [<c08999a4>] (bus_add_driver+0x154/0x1e0) > [ 15.440946] [<c08999a4>] (bus_add_driver) from [<c089ba38>] (driver_register+0x74/0x108) > [ 15.441020] [<c089ba38>] (driver_register) from [<c144edb8>] (imx_uart_init+0x20/0x40) > [ 15.441090] [<c144edb8>] (imx_uart_init) from [<c010232c>] (do_one_initcall+0x80/0x3ac) > [ 15.441162] [<c010232c>] (do_one_initcall) from [<c1400ff0>] (kernel_init_freeable+0x170/0x204) > [ 15.441241] [<c1400ff0>] (kernel_init_freeable) from [<c0dd5c48>] (kernel_init+0x8/0x118) > [ 15.441313] [<c0dd5c48>] (kernel_init) from [<c0100134>] (ret_from_fork+0x14/0x20) > [ 15.441414] Exception stack(0xc609ffb0 to 0xc609fff8) > [ 15.441571] ffa0: 00000000 00000000 00000000 00000000 > [ 15.441738] ffc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 > [ 15.441872] ffe0: 00000000 00000000 00000000 00000000 00000013 00000000 Thanks for your answer! [1] https://lore.kernel.org/r/1593618100-2151-1-git-send-email-prabhakar.mahadev-lad.rj@xxxxxxxxxxxxxx Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds
