linux-kernel - Re: [PATCH] tty: serial: meson

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Message-ID: <20200705112222.GO3703480@smile.fi.intel.com>
Date:   Sun, 5 Jul 2020 14:22:22 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Marc Zyngier <maz@...nel.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Kevin Hilman <khilman@...libre.com>,
        "open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>,
        linux-amlogic@...ts.infradead.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        kernel-team@...roid.com
Subject: Re: [PATCH] tty: serial: meson_uart: Init port lock early

On Sun, Jul 05, 2020 at 11:28:56AM +0100, Marc Zyngier wrote:
> On 2020-07-05 11:07, Andy Shevchenko wrote:
> > On Sun, Jul 5, 2020 at 12:32 PM Marc Zyngier <maz@...nel.org> wrote:
> > > 
> > > The meson UART driver triggers a lockdep splat at boot time, due
> > > to the new expectation that the driver has to initialize the
> > > per-port spinlock itself.
> > > 
> > > It remains unclear why a double initialization of the port
> > > spinlock is a desirable outcome, but in the meantime let's
> > > fix the splat.
> > > 
> > 
> > Thanks!
> > 
> > Can you test patch from [1] if it helps and doesn't break anything in
> > your case?
> > 
> > [1]:
> > https://lore.kernel.org/linux-serial/20200217114016.49856-1-andriy.shevchenko@linux.intel.com/T/#m9255e2a7474b160e66c7060fca5323ca3df49cfd
> 
> On its own, this patch doesn't seem to cure the issue (and it
> adds a compile-time warning due to unused flags).

Ah, sorry, I didn't compile it.
And after second though I think we simple need to initialise spin lock there.
Can you try below (compile-tested only):

>From ed4c882e7dc3fdfcea706ada0678c060c36163b3 Mon Sep 17 00:00:00 2001
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Date: Sat, 4 Jul 2020 19:30:39 +0300
Subject: [PATCH 1/1] serial: core: Initialise spin lock before use in
 uart_configure_port()

In case of the port to be used as a console we must initialise
a spin lock before use.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
---
 drivers/tty/serial/serial_core.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index 3cc183acf7ba..a81b4900eb60 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -2371,6 +2371,13 @@ uart_configure_port(struct uart_driver *drv, struct uart_state *state,
 		/* Power up port for set_mctrl() */
 		uart_change_pm(state, UART_PM_STATE_ON);
 
+		/*
+		 * If this driver supports console, and it hasn't been
+		 * successfully registered yet, initialise spin lock for it.
+		 */
+		if (port->cons && !(port->cons->flags & CON_ENABLED))
+			spin_lock_init(&port->lock);
+
 		/*
 		 * Ensure that the modem control lines are de-activated.
 		 * keep the DTR setting that is set in uart_set_options()
-- 
2.27.0



> Or did you mean to test it in complement of my patch?

No, the idea to avoid "fixing" driver as you rightfully noticed a double init issue.

-- 
With Best Regards,
Andy Shevchenko