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Commit 6b4e4467 authored by John Ogness's avatar John Ogness Committed by Greg Kroah-Hartman
Browse files

serial: meson: acquire port->lock in startup() 

[ Upstream commit 589f892ac8ef244e47c5a00ffd8605daa1eaef8e ]

The uart_ops startup() callback is called without interrupts
disabled and without port->lock locked, relatively late during the
boot process (from the call path of console_on_rootfs()). If the
device is a console, it was already previously registered and could
be actively printing messages.

Since the startup() callback is reading/writing registers used by
the console write() callback (AML_UART_CONTROL), its access must
be synchronized using the port->lock. Currently it is not.

The startup() callback is the only function that explicitly enables
interrupts. Without the synchronization, it is possible that
interrupts become accidentally permanently disabled.

CPU0                           CPU1
meson_serial_console_write     meson_uart_startup
--------------------------     ------------------
spin_lock(port->lock)
val = readl(AML_UART_CONTROL)
uart_console_write()
                               writel(INT_EN, AML_UART_CONTROL)
writel(val, AML_UART_CONTROL)
spin_unlock(port->lock)

Add port->lock synchronization to meson_uart_startup() to avoid
racing with meson_serial_console_write().

Also add detailed comments to meson_uart_reset() explaining why it
is *not* using port->lock synchronization.

Link: https://lore.kernel.org/lkml/2a82eae7-a256-f70c-fd82-4e510750906e@samsung.com


Fixes: ff7693d0 ("ARM: meson: serial: add MesonX SoC on-chip uart driver")
Reported-by: default avatarMarek Szyprowski <m.szyprowski@samsung.com>
Tested-by: default avatarMarek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: default avatarPetr Mladek <pmladek@suse.com>
Reviewed-by: default avatarJiri Slaby <jirislaby@kernel.org>
Acked-by: default avatarNeil Armstrong <narmstrong@baylibre.com>
Signed-off-by: default avatarJohn Ogness <john.ogness@linutronix.de>
Link: https://lore.kernel.org/r/20220508103547.626355-1-john.ogness@linutronix.de


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
parent 6ecd4d5c

drivers/tty/serial/meson_uart.c

+13 −0
Original line number Diff line number Diff line
@@ -255,6 +255,14 @@ static const char *meson_uart_type(struct uart_port *port) 
	return (port->type == PORT_MESON) ? "meson_uart" : NULL;

}



/*

 * This function is called only from probe() using a temporary io mapping

 * in order to perform a reset before setting up the device. Since the

 * temporarily mapped region was successfully requested, there can be no

 * console on this port at this time. Hence it is not necessary for this

 * function to acquire the port->lock. (Since there is no console on this

 * port at this time, the port->lock is not initialized yet.)

 */

static void meson_uart_reset(struct uart_port *port)

{

	u32 val;
@@ -269,9 +277,12 @@ static void meson_uart_reset(struct uart_port *port) 


static int meson_uart_startup(struct uart_port *port)

{

	unsigned long flags;

	u32 val;

	int ret = 0;



	spin_lock_irqsave(&port->lock, flags);



	val = readl(port->membase + AML_UART_CONTROL);

	val |= AML_UART_CLEAR_ERR;

	writel(val, port->membase + AML_UART_CONTROL);
@@ -287,6 +298,8 @@ static int meson_uart_startup(struct uart_port *port) 
	val = (AML_UART_RECV_IRQ(1) | AML_UART_XMIT_IRQ(port->fifosize / 2));

	writel(val, port->membase + AML_UART_MISC);



	spin_unlock_irqrestore(&port->lock, flags);



	ret = request_irq(port->irq, meson_uart_interrupt, 0,

			  port->name, port);