linux-kernel - Re: [RFC][PATCH] serial: amba-pl011: Make sure we initialize the port.lock spinlock

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Date:   Fri, 24 Apr 2020 00:14:46 +0100
From:   Valentin Schneider <valentin.schneider@....com>
To:     John Stultz <john.stultz@...aro.org>
Cc:     lkml <linux-kernel@...r.kernel.org>,
        Russell King <linux@...linux.org.uk>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>, linux-serial@...r.kernel.org
Subject: Re: [RFC][PATCH] serial: amba-pl011: Make sure we initialize the port.lock spinlock


Hi John,

On 23/04/20 23:00, John Stultz wrote:
> Which seems to be due to the fact that after allocating the uap
> structure, the pl011 code doesn't initialize the spinlock.
>
> This patch fixes it by initializing the spinlock and the warning
> has gone away.
>

Thanks for having a look. It does seem like the reasonable thing to do, and
I no longer get the warning on h960.

That said, I got more curious as this doesn't show up on my Juno (same
Image). Digging into it I see that uart_add_one_port() has a call to
uart_port_spin_lock_init() a few lines before uart_configure_port() (in
which the above warning gets triggered). That thing says:

 * Ensure that the serial console lock is initialised early.
 * If this port is a console, then the spinlock is already initialised.

Which requires me to ask: are we doing the right thing here?

> CC: Valentin Schneider <valentin.schneider@....com>
> Cc: Russell King <linux@...linux.org.uk>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: Jiri Slaby <jslaby@...e.com>
> Cc: linux-serial@...r.kernel.org
> Reported-by: Valentin Schneider <valentin.schneider@....com>
> Signed-off-by: John Stultz <john.stultz@...aro.org>
> ---
>  drivers/tty/serial/amba-pl011.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
> index 2296bb0f9578..458fc3d9d48c 100644
> --- a/drivers/tty/serial/amba-pl011.c
> +++ b/drivers/tty/serial/amba-pl011.c
> @@ -2575,6 +2575,7 @@ static int pl011_setup_port(struct device *dev, struct uart_amba_port *uap,
>       uap->port.has_sysrq = IS_ENABLED(CONFIG_SERIAL_AMBA_PL011_CONSOLE);
>       uap->port.flags = UPF_BOOT_AUTOCONF;
>       uap->port.line = index;
> +	spin_lock_init(&uap->port.lock);
>
>       amba_ports[index] = uap;